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  • 1. 1 Conservation Biology for All EDITED BY: Navjot S. Sodhi Department of Biological Sciences, National University of Singapore AND *Department of Organismic and Evolutionary Biology, Harvard University (*Address while the book was prepared) Paul R. Ehrlich Department of Biology, Stanford University 1© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 2. Sodhi and Ehrlich: Conservation Biology for All. 3 Great Clarendon Street, Oxford OX2 6DP Oxford University Press is a department of the University of Oxford. It furthers the Universitys objective of excellence in research, scholarship, and education by publishing worldwide in Oxford New York Auckland Cape Town Dar es Salaam Hong Kong Karachi Kuala Lumpur Madrid Melbourne Mexico City Nairobi New Delhi Shanghai Taipei Toronto With offices in Argentina Austria Brazil Chile Czech Republic France Greece Guatemala Hungary Italy Japan Poland Portugal Singapore South Korea Switzerland Thailand Turkey Ukraine Vietnam Oxford is a registered trade mark of Oxford University Press in the UK and in certain other countries Published in the United States by Oxford University Press Inc., New York # Oxford University Press 2010 The moral rights of the authors have been asserted Database right Oxford University Press (maker) First published 2010 Reprinted with corrections 2010 Available online with corrections, January 2011 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of Oxford University Press, or as expressly permitted by law, or under terms agreed with the appropriate reprographics rights organization. Enquiries concerning reproduction outside the scope of the above should be sent to the Rights Department, Oxford University Press, at the address above You must not circulate this book in any other binding or cover and you must impose the same condition on any acquirer British Library Cataloguing in Publication Data Data available Library of Congress Cataloging in Publication Data Data available Typeset by SPI Publisher Services, Pondicherry, India Printed in Great Britain on acid-free paper by CPI Antony Rowe, Chippenham, Wiltshire ISBN 978–0–19–955423–2 (Hbk.) ISBN 978–0–19–955424–9 (Pbk.) 3 5 7 9 10 8 6 4 2© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 3. 1 ContentsDedication xiAcknowledgements xiiList of Contributors xiiiForeword Georgina Mace xviiIntroduction Navjot S. Sodhi and Paul R. Ehrlich 1 Introduction Box 1: Human population and conservation (Paul R. Ehrlich) 2 Introduction Box 2: Ecoethics (Paul R. Ehrlich) 31: Conservation biology: past and present Curt Meine 7 1.1 Historical foundations of conservation biology 7 Box 1.1: Traditional ecological knowledge and biodiversity conservation (Fikret Berkes) 8 1.2 Establishing a new interdisciplinary field 12 1.3 Consolidation: conservation biology secures its niche 15 1.4 Years of growth and evolution 16 Box 1.2: Conservation in the Philippines (Mary Rose C. Posa) 19 1.5 Conservation biology: a work in progress 21 Summary 21 Suggested reading 22 Relevant websites 222: Biodiversity Kevin J. Gaston 27 2.1How much biodiversity is there? 27 2.2How has biodiversity changed through time? 33 2.3Where is biodiversity? 35 2.4In conclusion 39 Box 2.1: Invaluable biodiversity inventories (Navjot S. Sodhi) 40 Summary 41 Suggested reading 41 Revelant websites 423: Ecosystem functions and services Cagan H. Sekercioglu 45 3.1 Climate and the Biogeochemical Cycles 45 3.2 Regulation of the Hydrologic Cycle 48© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 4. Sodhi and Ehrlich: Conservation Biology for All. CONTENTS 3.3 Soils and Erosion 50 3.4 Biodiversity and Ecosystem Function 51 Box 3.1: The costs of large-mammal extinctions (Robert M. Pringle) 52 Box 3.2: Carnivore conservation (Mark S. Boyce) 54 Box 3.3: Ecosystem services and agroecosystems in a landscape context (Teja Tscharntke) 55 3.5 Mobile Links 57 Box 3.4: Conservation of plant-animal mutualisms (Priya Davidar) 58 Box 3.5: Consequences of pollinator decline for the global food supply (Claire Kremen) 60 3.6 Nature’s Cures versus Emerging Diseases 64 3.7 Valuing Ecosystem Services 65 Summary 66 Relevant websites 67 Acknowledgements 674: Habitat destruction: death by a thousand cuts William F. Laurance 73 4.1 Habitat loss and fragmentation 73 4.2 Geography of habitat loss 73 Box 4.1: The changing drivers of tropical deforestation (William F. Laurance) 75 4.3 Loss of biomes and ecosystems 76 Box 4.2: Boreal forest management: harvest, natural disturbance, and climate change (Ian G. Warkentin) 80 4.4 Land‐use intensification and abandonment 82 Box 4.3: Human impacts on marine ecosystems (Benjamin S. Halpern, Carrie V. Kappel, Fiorenza Micheli, and Kimberly A. Selkoe) 83 Summary 86 Suggested reading 86 Relevant websites 865: Habitat fragmentation and landscape change Andrew F. Bennett and Denis A. Saunders 88 5.1 Understanding the effects of landscape change 88 5.2 Biophysical aspects of landscape change 90 5.3 Effects of landscape change on species 92 Box 5.1: Time lags and extinction debt in fragmented landscapes (Andrew F. Bennett and Denis A. Saunders) 92 5.4 Effects of landscape change on communities 96 5.5 Temporal change in fragmented landscapes 99 5.6 Conservation in fragmented landscapes 99 Box 5.2: Gondwana Link: a major landscape reconnection project (Andrew F. Bennett and Denis A. Saunders) 101 Box 5.3: Rewilding (Paul R. Ehrlich) 102 Summary 104 Suggested reading 104 Relevant websites 1046: Overharvesting Carlos A. Peres 107 6.1 A brief history of exploitation 108 6.2 Overexploitation in tropical forests 110© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 5. 1 CONTENTS vii 6.3 Overexploitation in aquatic ecosystems 113 6.4 Cascading effects of overexploitation on ecosystems 115 Box 6.1: The state of fisheries (Daniel Pauly) 118 6.5 Managing overexploitation 120 Box 6.2: Managing the exploitation of wildlife in tropical forests (Douglas W. Yu) 121 Summary 126 Relevant websites 1267: Invasive species Daniel Simberloff 131 Box 7.1: Native invasives (Daniel Simberloff ) 131 Box 7.2: Invasive species in New Zealand (Daniel Simberloff ) 132 7.1 Invasive species impacts 133 7.2 Lag times 143 7.3 What to do about invasive species 144 Summary 148 Suggested reading 148 Relevant websites 1488: Climate change Thomas E. Lovejoy 153 8.1 Effects on the physical environment 153 8.2 Effects on biodiversity 154 Box 8.1: Lowland tropical biodiversity under global warming (Navjot S. Sodhi) 156 8.3 Effects on biotic interactions 158 8.4 Synergies with other biodiversity change drivers 159 8.5 Mitigation 159 Box 8.2: Derivative threats to biodiversity from climate change (Paul R. Ehrlich) 160 Summary 161 Suggested reading 161 Relevant websites 1619: Fire and biodiversity David M. J. S. Bowman and Brett P. Murphy 163 9.1 What is fire? 164 9.2 Evolution and fire in geological time 164 9.3 Pyrogeography 165 Box 9.1: Fire and the destruction of tropical forests (David M. J. S. Bowman and Brett P. Murphy) 167 9.4 Vegetation–climate patterns decoupled by fire 167 9.5 Humans and their use of fire 170 Box 9.2: The grass-fire cycle (David M. J. S. Bowman and Brett P. Murphy) 171 Box 9.3: Australia’s giant fireweeds (David M. J. S. Bowman and Brett P. Murphy) 173 9.6 Fire and the maintenance of biodiversity 173 9.7 Climate change and fire regimes 176 Summary 177 Suggested reading 178 Relevant websites 178 Acknowledgements 178© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 6. Sodhi and Ehrlich: Conservation Biology for All. CONTENTS10: Extinctions and the practice of preventing them Stuart L. Pimm and Clinton N. Jenkins 181 10.1 Why species extinctions have primacy 181 Box 10.1: Population conservation (Jennifer B.H. Martiny) 182 10.2 How fast are species becoming extinct? 183 10.3 Which species become extinct? 186 10.4 Where are species becoming extinct? 187 10.5 Future extinctions 192 10.6 How does all this help prevent extinctions? 195 Summary 196 Suggested reading 196 Relevant websites 19611: Conservation planning and priorities Thomas Brooks 199 11.1 Global biodiversity conservation planning and priorities 199 11.2 Conservation planning and priorities on the ground 204 Box 11.1: Conservation planning for Key Biodiversity Areas in Turkey (Güven Eken, g _ Murat Ataol, Murat Bozdoan, Özge Balkız, Süreyya Isfendiyarolu, g Dicle Tuba Kılıç, and Yıldıray Lise) 209 11.3 Coda: the completion of conservation planning 213 Summary 214 Suggested reading 214 Relevant websites 214 Acknowledgments 21512: Endangered species management: the US experience David. S. Wilcove 220 12.1 Identification 220 Box 12.1: Rare and threatened species and conservation planning in Madagascar (Claire Kremen, Alison Cameron, Tom Allnutt, and Andriamandimbisoa Razafimpahanana) 221 Box 12.2: Flagship species create Pride (Peter Vaughan) 223 12.2 Protection 226 12.3 Recovery 230 12.4 Incentives and disincentives 232 12.5 Limitations of endangered species programs 233 Summary 234 Suggested reading 234 Relevant websites 23413: Conservation in human-modified landscapes Lian Pin Koh and Toby A. Gardner 236 13.1 A history of human modification and the concept of “wild nature” 236 Box 13.1: Endocrine disruption and biological diversity (J. P. Myers) 237 13.2 Conservation in a human‐modified world 240 13.3 Selectively logged forests 242 13.4 Agroforestry systems 243© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 7. 1 CONTENTS ix 13.5 Tree plantations 245 Box 13.2: Quantifying the biodiversity value of tropical secondary forests and exotic tree plantations (Jos Barlow) 247 13.6 Agricultural land 248 Box 13.3: Conservation in the face of oil palm expansion (Matthew Struebig, Ben Phalan, and Emily Fitzherbert) 249 Box 13.4: Countryside biogeography: harmonizing biodiversity and agriculture ( Jai Ranganathan and Gretchen C. Daily) 251 13.7 Urban areas 253 13.8 Regenerating forests on degraded land 254 13.9 Conservation and human livelihoods in modified landscapes 255 13.10 Conclusion 256 Summary 257 Suggested reading 257 Relevant websites 25814: The roles of people in conservation C. Anne Claus, Kai M. A. Chan, and Terre Satterfield 262 14.1 A brief history of humanity’s influence on ecosystems 262 14.2 A brief history of conservation 262 Box 14.1: Customary management and marine conservation (C. Anne Claus, Kai M. A. Chan, and Terre Satterfield) 264 Box 14.2: Historical ecology and conservation effectiveness in West Africa (C. Anne Claus, Kai M. A. Chan, and Terre Satterfield) 265 14.3 Common conservation perceptions 265 Box 14.3: Elephants, animal rights, and Campfire (Paul R. Ehrlich) 267 14.4 Factors mediating human‐environment relations 269 Box 14.4: Conservation, biology, and religion (Kyle S. Van Houtan) 270 14.5 Biodiversity conservation and local resource use 273 14.6 Equity, resource rights, and conservation 275 Box 14.5: Empowering women: the Chipko movement in India (Priya Davidar) 276 14.7 Social research and conservation 278 Summary 281 Relevant websites 281 Suggested reading 28115: From conservation theory to practice: crossing the divide Madhu Rao and Joshua Ginsberg 284 Box 15.1: Swords into Ploughshares: reducing military demand for wildlife products (Lisa Hickey, Heidi Kretser, Elizabeth Bennett, and McKenzie Johnson) 285 Box 15.2: The World Bank and biodiversity conservation (Tony Whitten) 286 Box 15.3: The Natural Capital Project (Heather Tallis, Joshua H. Goldstein, and Gretchen C. Daily) 288 15.1 Integration of Science and Conservation Implementation 290 Box 15.4: Measuring the effectiveness of conservation spending (Matthew Linkie and Robert J. Smith) 291 15.2 Looking beyond protected areas 292 Box 15.5: From managing protected areas to conserving landscapes (Karl Didier) 293© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 8. Sodhi and Ehrlich: Conservation Biology for All. CONTENTS 15.3 Biodiversity and human poverty 293 Box 15.6: Bird nest protection in the Northern Plains of Cambodia (Tom Clements) 297 Box 15.7: International activities of the Missouri Botanical Garden (Peter Raven) 301 15.4 Capacity needs for practical conservation in developing countries 303 15.5 Beyond the science: reaching out for conservation 304 15.6 People making a difference: A Rare approach 305 15.7 Pride in the La Amistad Biosphere Reserve, Panama 305 15.8 Outreach for policy 306 15.9 Monitoring of Biodiversity at Local and Global Scales 306 Box 15.8: Hunter self-monitoring by the Isoseño-Guaranı´ in the Bolivian Chaco ( Andrew Noss) 307 Summary 310 Suggested reading 310 Relevant websites 31016: The conservation biologist’s toolbox – principles for the design and analysis of conservation studies Corey J. A. Bradshaw and Barry W. Brook 313 16.1 Measuring and comparing ‘biodiversity’ 314 Box 16.1: Cost effectiveness of biodiversity monitoring (Toby Gardner) 314 Box 16.2: Working across cultures (David Bickford) 316 16.2 Mensurative and manipulative experimental design 319 Box 16.3: Multiple working hypotheses (Corey J. A. Bradshaw and Barry W. Brook) 321 Box 16.4: Bayesian inference (Corey J. A. Bradshaw and Barry W. Brook) 324 16.3 Abundance Time Series 326 16.4 Predicting Risk 328 16.5 Genetic Principles and Tools 330 Box 16.5: Functional genetics and genomics (Noah K. Whiteman) 331 16.6 Concluding Remarks 333 Box 16.6: Useful textbook guides (Corey J. A. Bradshaw and Barry W. Brook) 334 Summary 335 Suggested reading 335 Relevant websites 335 Acknowledgements 336Index 341© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 9. 1 DedicationNSS: To those who have or want to make the difference.PRE: To my mentors—Charles Birch, Charles Michener, and Robert Sokal.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 10. Sodhi and Ehrlich: Conservation Biology for All. AcknowledgementsNSS thanks the Sarah and Daniel Hrdy Fellowship Wren Wirth, and the Mertz Gilmore Foundationin Conservation Biology (Harvard University) and for their support. We thank Mary Rose C. Posa, Peithe National University of Singapore for support Xin, Ross McFarland, Hugh Tan, and Peter Ngwhile this book was prepared. He also thanks for their invaluable assistance. We also thankNaomi Pierce for providing him with an office. Ian Sherman, Helen Eaton, and Carol Bestley atPRE thanks Peter and Helen Bing, Larry Condon, Oxford University Press for their help/support.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 11. 1 List of ContributorsTom Allnutt Murat Bozdoan gDepartment of Environmental Sciences, Policy and g g Doa Dernei, Hürriyet Cad. 43/12 Dikmen, Ankara,Management, 137 Mulford Hall, University of Califor- Turkey.nia, Berkeley, CA 94720-3114, USA. Corey J. A. BradshawMurat Ataol Environment Institute, School of Earth and Environ- g gDoa Dernei, Hürriyet Cad. 43/12 Dikmen, Ankara, mental Sciences, University of Adelaide, South Aus-Turkey. tralia 5005 AND South Australian Research and Development Institute, P.O. Box 120, Henley Beach,Özge Balkız South Australia 5022, Australia. g gDoa Dernei, Hürriyet Cad. 43/12 Dikmen, Ankara,Turkey. Barry W. Brook Environment Institute, School of Earth and Environmen-Jos Barlow tal Sciences, University of Adelaide, South AustraliaLancaster Environment Centre, Lancaster University, 5005, Australia.Lancaster, LA1 4YQ, UK. Thomas BrooksAndrew F. Bennett Center for Applied Biodiversity Science, ConservationSchool of Life and Environmental Sciences, Deakin International, 2011 Crystal Drive Suite 500, Arling-University, 221 Burwod Highway, Burwood, VIC ton VA 22202, USA; World Agroforestry Center3125, Australia. (ICRAF), University of the Philippines Los Baños,Elizabeth Bennett Laguna 4031, Philippines; AND School of GeographyWildlife Conservation Society, 2300 Southern Boule- and Environmental Studies, University of Tasmania,vard., Bronx, NY 10464-1099, USA. Hobart TAS 7001, Australia.Fikret Berkes Alison CameronNatural Resources Institute, 70 Dysart Road, University Max Planck Institute for Ornithology, Eberhard-of Manitoba, Winnipeg MB R3T 2N2, Canada. Gwinner-Straße, 82319 Seewiesen, Germany.David Bickford Kai M. A. ChanDepartment of Biological Sciences, National University Institute for Resources, Environment and Sustainability,of Singapore, 14 Science Drive 4, Singapore 117543, University of British Columbia, Vancouver, BritishRepublic of Singapore. Columbia V6T 1Z4, Canada.David M. J. S. Bowman C. Anne ClausSchool of Plant Science, University of Tasmania, Private Departments of Anthropology and Forestry Envi-Bag 55, Hobart, TAS 7001, Australia. ronmental Studies, Yale University,10 Sachem Street, New Haven, CT 06511, USA.Mark S. BoyceDepartment of Biological Sciences, University of Tom ClementsAlberta, Edmonton, Alberta T6G 2E9, Canada. Wildlife Conservation Society, Phnom Penh, Cambodia.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 12. Sodhi and Ehrlich: Conservation Biology for All. LIST OF CONTRIBUTORSGretchen C. Daily _ Süreyya Isfendiyarolu gCenter for Conservation Biology, Department of Biology, g g Doa Dernei, Hürriyet Cad. 43/12 Dikmen, Ankara,and Woods Institute, 371 Serra Mall, Stanford Univer- Turkey.sity, Stanford, CA 94305-5020, USA. Clinton N. JenkinsPriya Davidar Nicholas School of the Environment, Duke University,School of Life Sciences, Pondicherry University, Kalapet, Box 90328, LSRC A201, Durham, NC 27708, USA.Pondicherry 605014, India. McKenzie JohnsonKarl Didier Wildlife Conservation Society, 2300 Southern Boule-Wildlife Conservation Society, 2300 Southern Boule- vard, Bronx, NY 10464-1099, USA.vard, Bronx, NY 10464-1099, USA. Carrie V. KappelPaul R. Ehrlich National Center for Ecological Analysis and Synthe-Center for Conservation Biology, Department of Biol- sis, 735 State Street, Santa Barbara, CA 93101, USA.ogy, Stanford University, Stanford, CA 94305-5020, Dicle Tuba KılıçUSA. g g Doa Dernei, Hürriyet Cad. 43/12 Dikmen, Ankara,Güven Eken Turkey. g gDoa Dernei, Hürriyet Cad. 43/12 Dikmen, Ankara, Lian Pin KohTurkey. Institute of Terrestrial Ecosystems, Swiss Federal In- stitute of Technology (ETH Zürich), CHN G 74.2,Emily Fitzherbert Universitätstrasse 16, Zurich 8092, Switzerland.Institute of Zoology, Zoological Society of London,Regent’s Park, London, NW1 4RY, UK. Claire Kremen Department of Environmental Sciences, Policy andToby A. Gardner Management, 137 Mulford Hall, University of Cali-Department of Zoology, University of Cambridge, fornia, Berkeley, CA 94720-3114, USA.Downing Street, Cambridge, CB2 3EJ, UK ANDDepartamento de Biologia, Universidade Federal de Heidi KretserLavras, Lavras, Minas Gerais, 37200-000, Brazil. Wildlife Conservation Society, 2300 Southern Boule- vard, Bronx, NY 10464-1099, USA.Kevin J. GastonDepartment of Animal Plant Sciences, University William F. Lauranceof Sheffield, Sheffield, S10 2TN, UK. Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancón, Republic of Panama.Joshua GinsbergWildlife Conservation Society, 2300 Southern Boule- Matthew Linkievard, Bronx, NY 10464-1099, USA. Fauna Flora International, 4th Floor, Jupiter House, Station Road, Cambridge, CB1 2JD, UK.Joshua H. GoldsteinHuman Dimensions of Natural Resources, Warner Yıldıray LiseCollege of Natural Resources, Colorado State Univer- g g Doa Dernei, Hürriyet Cad. 43/12 Dikmen, Ankara,sity, Fort Collins, CO 80523-1480, USA. Turkey.Benjamin S. Halpern Thomas E. LovejoyNational Center for Ecological Analysis and The H. John Heinz III Center for Science, EconomicsSynthesis, 735 State Street, Santa Barbara, CA and the Environment, 900 17th Street NW, Suite 700,93101, USA. Washington, DC 20006, USA.Lisa Hickey Jennifer B. H. MartinyWildlife Conservation Society, 2300 Southern Boule- Department of Ecology and Evolutionary Biology,vard, Bronx, NY 10464-1099, USA. University of California, Irvine, CA 92697, USA.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 13. 1 LIST OF CONTRIBUTORS xvCurt Meine Madhu RaoAldo Leopold Foundation/International Crane Wildlife Conservation Society Asia Program 2300Foundation, P.O. Box 38, Prairie du Sac, WI S. Blvd., Bronx, New York, NY 10460, USA.53578, USA. Peter RavenFiorenza Micheli Missouri Botanical Garden, Post Office Box 299, St.Hopkins Marine Station, Stanford University, Pacific Louis, MO 63166-0299, USA.Grove, CA 93950, USA. Andriamandimbisoa RazafimpahananaBrett P. Murphy Réseau de la Biodiversité de Madagascar, WildlifeSchool of Plant Science, University of Tasmania, Pri- Conservation Society, Villa Ifanomezantsoa, Soavim-vate Bag 55, Hobart, TAS 7001, Australia. bahoaka, Boîte Postale 8500, Antananarivo 101, Ma- dagascar.J. P. MyersEnvironmental Health Sciences, 421 E Park Street, Terre SatterfieldCharlottesville VA 22902, USA. Institute for Resources, Environment and Sustainabil- ity, University of British Columbia, Vancouver, Brit-Andrew Noss ish Columbia V6T 1Z4, Canada.Proyecto Gestión Integrada de Territorios IndigenasWCS-Ecuador, Av. Eloy Alfaro N37-224 y Coremo Denis A. SaundersApartado, Postal 17-21-168, Quito, Ecuador. CSIRO Sustainable Ecosystems, GPO Box 284, Can- berra, ACT 2601, Australia.Daniel PaulySeas Around Us Project, University of British Colum- Cagan H. Sekercioglubia, Vancouver, British Columbia, V6T 1Z4, Canada. Center for Conservation Biology, Department of Biology, Stanford University, Stanford, CA 94305-5020, USA.Carlos A. Peres Kimberly A. SelkoeSchool of Environmental Sciences, University of East National Center for Ecological Analysis and Synthe-Anglia, Norwich, NR4 7TJ, UK. sis, 735 State Street, Santa Barbara, CA 93101, USA.Ben Phalan Daniel SimberloffConservation Science Group, Department of Zoology, Department of Ecology and Evolutionary Biology,University of Cambridge, Downing Street, Cam- University of Tennessee, Knoxville, TN 37996,bridge, CB2 3EJ, UK. USA.Stuart L. Pimm Robert J. SmithNicholas School of the Environment, Duke University, Durrell Institute of Conservation and Ecology,Box 90328, LSRC A201, Durham, NC 27708, USA. University of Kent, Canterbury, Kent, CT2 7NR,Mary Rose C. Posa UK.Department of Biology, National University of Singa- Navjot S. Sodhipore, 14 Science Drive 4, Singapore 117543, Republic Department of Biological Sciences, National Univer-of Singapore. sity of Singapore, 14 Science Drive 4, SingaporeRobert M. Pringle 117543, Republic of Singapore AND Department ofDepartment of Biology, Stanford University, Stan- Organismic and Evolutionary Biology, Harvard Uni-ford, CA 94305, USA. versity, Cambridge, MA 02138, USA.Jai Ranganathan Matthew StruebigNational Center for Ecological Analysis and Synthe- School of Biological Chemical Sciences, Queensis, 735 State Street, Suite 300 Santa Barbara, CA Mary, University of London, Mile End Road, London,93109, USA. E1 4NS, UK.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 14. Sodhi and Ehrlich: Conservation Biology for All. LIST OF CONTRIBUTORSHeather Tallis Ian G. WarkentinThe Natural Capital Project, Woods Institute for the Environmental Science – Biology, Memorial Univer-Environment, 371 Serra Mall, Stanford University, sity of Newfoundland, Corner Brook, NewfoundlandStanford, CA 94305-5020, USA. and Labrador A2H 6P9, Canada. Noah K. WhitemanTeja Tscharntke Department of Organismic and Evolutionary Biol-Agroecology, University of Göttingen, Germany. ogy, Harvard University, Cambridge, MA 02138, USA.Kyle S. Van Houtan Tony WhittenDepartment of Biology, O W Rollins Research Ctr, The World Bank, Washington, DC, USA.1st Floor, 1510 Clifton Road, Lab# 1112 EmoryUniversity AND Center for Ethics, 1531 Dickey David WilcoveDrive, Emory University, Atlanta, GA 30322, Department of Ecology and Evolutionary Biology,USA. Princeton University, Princeton, NJ 08544-1003, USA.Peter Vaughan Douglas W. YuRare, 1840 Wilson Boulevard, Suite 204, Arlington, School of Biological Sciences, University of EastVA 22201, USA. Anglia, Norwich, NR4 7TJ, UK.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 15. 1 Foreword2010 was named by the United Nations to be the servation biology relevant to and applicable byInternational Year of Biodiversity, coinciding all is therefore a key task.with major political events that set the stage for It is in this context that Navjot Sodhi and Paula radical review of the way we treat our environ- Ehlrich have contributed this important book.ment and its biological riches. So far, the reports Covering all aspects of conservation biologyhave been dominated by reconfirmations that from the deleterious drivers, through to the im-people and their lifestyles continue to deplete pacts on people, and providing tools, techniques,the earth’s biodiversity. We are still vastly over- and background to practical solutions, the bookspending our natural capital and thereby depriv- provides a resource for many different peopleing future generations. If that were not bad and contexts. Written by the world’s leading ex-enough news in itself, there are no signs that perts you will find clear summaries of the latestactions to date have slowed the rate of depletion. literature on how to decide what to do, and thenIn fact, it continues to increase, due largely to how to do it. Presented in clear and accessiblegrowing levels of consumption that provide in- text, this book will support the work of manycreasingly unequal benefits to different groups of people. There are different kinds of conservationpeople. actions, at different scales, and affecting different It is easy to continue to delve into the patterns parts of the biosphere, all laid out clearly andand processes that lie at the heart of the problem. concisely.But it is critical that we also start to do everything There is something in here for everyone who is,we can to reverse all the damaging trends. These or wishes to be, a conservation biologist. I amactions cannot and should not be just the respon- sure you will all be inspired and better informedsibility of governments and their agencies. It to do something that will improve the prospectsmust be the responsibility of all of us, including for all, so that in a decade or so, when the worldscientists, wildlife managers, naturalists, and in- community next examines the biodiversity ac-deed everyone who cares so that future genera- counts, things will definitely be taking a turn fortions can have the same choices and the same the better!opportunity to marvel at and benefit from nature, Georgina Mace CBE FRSas our generation has had. We all can be involved Imperial College Londonin actions to improve matters, and making con- 18 November 2010© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 16. 1 Introduction Navjot S. Sodhi and Paul R. EhrlichOur actions have put humanity into a deep envi- (e.g. food, medicines, pollination, pest control,ronmental crisis. We have destroyed, degraded, and flood protection).and polluted Earth’s natural habitats – indeed, Habitat loss and pollution are particularlyvirtually all of them have felt the influence of acute in developing countries, which are of spe-the dominant species. As a result, the vast major- cial concern because these harbor the greatestity of populations and species of plants and ani- species diversity and are the richest centers ofmals – key working parts of human life support endemism. Sadly, developing world conserva-systems – are in decline, and many are already tion scientists have found it difficult to afford anextinct. Increasing human population size and authoritative textbook of conservation biology,consumption per person (see Introduction Box which is particularly ironic, since it is these1) have precipitated an extinction crisis – the countries where the rates of habitat loss are high-“sixth mass extinction”, which is comparable to est and the potential benefits of superior informa-past extinction events such as the Cretaceous- tion in the hands of scientists and managers areTertiary mass extinction 65 million years ago therefore greatest. There is also now a pressingthat wiped out all the dinosaurs except for the need to educate the next generation of conserva-birds. Unlike the previous extinction events, tion biologists in developing countries, so thatwhich were attributed to natural catastrophes hopefully they are in a better position to protectincluding volcanic eruptions, meteorite impact their natural resources. With this book, we intendand global cooling, the current mass extinction to provide cutting-edge but basic conservationis exclusively humanity’s fault. Estimates indicate science to developing as well as developed coun-that numerous species and populations are cur- try inhabitants. The contents of this book arerently likely being extinguished every year. But freely available on the web.all is not lost – yet. Since our main aim is to make up-to-date conser- Being the dominant species on Earth, humans vation knowledge widely available, we have invit-have a moral obligation (see Introduction Box 2) ed many of the top names in conservation biologyto ensure the long-term persistence of rainfor- to write on specific topics. Overall, this book repre-ests, coral reefs, and tidepools as well as sagua- sents a project that the conservation communityro cacti, baobab trees, tigers, rhinos, pandas, has deemed worthy of support by donations ofbirds of paradise, morpho butterflies, and a time and effort. None of the authors, includingplethora of other creatures. All these landmarks ourselves, will gain financially from this project.and life make this planet remarkable – our It is our hope that this book will be of relevanceimagination will be bankrupt if wild nature is and use to both undergraduate and graduate stu-obliterated – even if civilization could survive dents as well as scientists, managers, and person-the disaster. In addition to moral and aesthetic nel in non-governmental organizations. The bookreasons, we have a selfish reason to preserve should have all the necessary topics to become anature – it provides society with countless and required reading for various undergraduate andinvaluable goods and absolutely crucial services graduate conservation-related courses. English is 1© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 17. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL Introduction Box 1 Human population and conservation Paul R. Ehrlich The size of the human population is mined and smelted today, water and petroleum approaching 7 billion people, and its most must come from lower quality sources, deeper fundamental connection with conservation is wells, or (for oil) from deep beneath the ocean simple: people compete with other animals, and must be transported over longer distances, which unlike green plants cannot make their all at ever‐greater environmental cost. own food. At present Homo sapiens uses, The tasks of conservation biologists are made coopts, or destroys close to half of all the food more difficult by human population growth, as available to the rest of the animal kingdom (see is readily seen in the I=PAT equation (Holdren Introduction Box 1 Figure). That means that, in and Ehrlich 1974; Ehrlich and Ehrlich 1981). essence, every human being added to the Impact (I) on biodiversity is not only a result of population means fewer individuals can be population size (P), but of that size multiplied supported in the remaining fauna. by affluence (A) measured as per capita But human population growth does much consumption, and that product multiplied by more than simply cause a proportional decline another factor (T), which summarizes the in animal biodiversity – since as you know, we technologies and socio‐political‐economic degrade nature in many ways besides arrangements to service that consumption. competing with animals for food. Each More people surrounding a rainforest reserve additional person will have a disproportionate in a poor nation often means more individuals negative impact on biodiversity in general. The invading the reserve to gather firewood or first farmers started farming the richest soils bush meat. More people in a rich country may they could find and utilized the richest and most mean more off‐road vehicles (ORVs) assaulting accessible resources first (Ehrlich and Ehrlich the biota – especially if the ORV manufacturers 2005). Now much of the soil that people first are politically powerful and can successfully farmed has been eroded away or paved over, fight bans on their use. As poor countries’ and agriculturalists increasingly are forced to populations grow and segments of them turn to marginal land to grow more food. become more affluent, demand rises for meat Equally, deeper and poorer ore deposits must be and automobiles, with domesticated animals continues Introduction Box 1 Figure Human beings consuming resources. Photograph by Mary Rose Posa. continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 18. 1 INTRODUCTION 3 Introduction Box 1 (Continued) to humanely lower birth rates until population competing with or devouring native biota, cars growth stops and begins a slow decline toward a causing all sorts of assaults on biodiversity, and sustainable size (Daily et al. 1994). both adding to climate disruption. Globally, as a growing population demands greater quantities of plastics, industrial chemicals, REFERENCES pesticides, fertilizers, cosmetics, and medicines, the toxification of the planet escalates, Anonymous. (2008). Welcome to the Anthropocene. bringing frightening problems for organisms Chemical and Engineering News, 86, 3. ranging from polar bears to frogs (to say Daily, G. C. and Ehrlich, A. H. (1994). Optimum human nothing of people!) (see Box 13.1). population size. Population and Environment, 15, In sum, population growth (along with 469–475. escalating consumption and the use of Ehrlich, P. R. and Ehrlich, A. H. (1981). Extinction: the environmentally malign technologies) is a major causes and consequences of the disappearance of driver of the ongoing destruction of species. Random House, New York, NY. populations, species, and communities that is a Ehrlich, P. R. and Ehrlich, A. H. (2005). One with Nineveh: salient feature of the Anthropocene politics, consumption, and the human future, (with new (Anonymous 2008). Humanity, as the dominant afterword). Island Press, Washington, DC. animal (Ehrlich and Ehrlich 2008), simply out Ehrlich, P. R. and Ehrlich, A. H. (2008). The Dominant competes other animals for the planet’s Animal: human evolution and the environment. Island productivity, and often both plants and animals Press, Washington, DC. for its freshwater. While dealing with more Holdren J. P. and Ehrlich, P. R. (1974). Human population limited problems, it therefore behooves every and the global environment. American Scientist, 62, conservation biologist to put part of her time 282–292. into restraining those drivers, including working Introduction Box 2 Ecoethics Paul R. Ehrlich The land ethic simply enlarges the boundaries of wielded by large‐scale institutions that try (and the community to include soils, waters, plants, sometimes succeed) to control broad aspects of and animals, or collectively: the land…. Aldo Leo- our global civilization. Those institutions pold (1949) include governments, religions, transnational corporations, and the like. To ignore these As you read this book, you should keep in mind power relations is, in essence, to ignore the that the problem of conserving biodiversity is most important large‐scale issues, such as replete with issues of practical ethics – agreed‐ conservation in the face of further human upon notions of the right or wrong of actual population growth and of rapid climate change behaviors (Singer 1993; Jamieson 2008). If – issues that demand global ethical discussion. civilization is to maintain the ecosystem services Small‐scale ecoethical dilemmas are (Chapter 3) that can support a sustainable commonly faced by conservation biologists. society and provide virtually everyone with a Should we eat shrimp in a restaurant when we reasonable quality of life, humanity will need can’t determine its provenance? Should we to focus much more on issues with a significant become more vegetarian? Is it legitimate to fly conservation connection, “ecoethics”. around the world in jet aircraft to try and Ultimately everything must be examined persuade people to change a lifestyle that from common “small‐scale” personal includes flying around the world in jet aircraft? ecoethical decisions to the ethics of power How should we think about all the trees cut continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 19. Sodhi and Ehrlich: Conservation Biology for All. Introduction Box 2 (Continued) down to produce the books and articles we’ve poor, while striving to limit aggregate con- written? These sorts of decisions are poignantly sumption by humanity. discussed by Bearzi (2009), who calls for • Start a global World War II type mobilization conservation biologists to think more carefully to shift to more benign energy technologies about their individual decisions and set a better and thus reduce the chances of a world‐wide example where possible. Some personal conservation disaster caused by rapid climate decisions are not so minor – such as how many change. children to have. But ironically Bearzi does not • Judge technologies not just on what they do discuss child‐bearing decisions, even though for people but also to people and the organ- especially in rich countries these are often the isms that are key parts of their life‐support most conservation‐significant ethical decisions systems. an individual makes. • Educate students, starting in kindergarten, Ecotourism is a hotbed of difficult ethical about the crucial need to preserve biodiversity issues, some incredibly complex, as shown in and expand peoples’ empathy not just to all Box 14.3. But perhaps the most vexing ethical human beings but also to the living elements in questions in conservation concern conflicts the natural world. between the needs and prerogatives of peoples Most conservation biologists view the task of and non‐human organisms. This is seen in issues preserving biodiversity as fundamentally one of like protecting reserves from people, where in ethics (Ehrlich and Ehrlich 1981). Nonetheless, the extreme some conservation biologists plead long experience has shown that arguments for strict exclusion of human beings based on a proposed ethical need to preserve (e.g. Terborgh 2004), and by the debates over our only known living relatives in the entire the preservation of endangered organisms and universe, the products of incredible traditional rights to hunt them. The latter is evolutionary sequences billions of years in exemplified by complex aboriginal extent, have largely fallen on deaf ears. Most “subsistence” whaling issues (Reeves 2002). ecologists have therefore switched to While commercial whaling is largely admittedly risky instrumental arguments for responsible for the collapse of many stocks, conservation (Daily 1997). What proportion of aboriginal whaling may threaten some of the conservation effort should be put into remnants. Does one then side with the whales promoting instrumental approaches that might or the people, to whom the hunts may be an backfire or be effective in only the short or important part of their tradition? Preserving middle term is an ethical‐tactical issue. the stocks by limiting aboriginal takes seems One of the best arguments for emphasizing the ecoethical thing to do, since it allows for the instrumental is that they can at least traditional hunting to persist, which will not buy time for the necessarily slow happen if the whales go extinct. Tradition is a cultural evolutionary process of tricky thing –coal mining or land development changing the norms that favor attention to may be family traditions, but ecoethically those reproducible capital and property rights to occupations should end. the near exclusion of natural capital. Perhaps most daunting of all is the task of Some day Aldo Leopold’s “Land Ethic” getting broad agreement from diverse cultures may become universal – until then on ecoethical issues. It has been suggested that conservation biologists will face many ethical a world‐wide Millennium Assessment of challenges. Human Behavior (MAHB) be established to, among other things, facilitate discussion and debate (Ehrlich and Kennedy 2005). My own views of the basic ecoethical paths that should be pursued follow. Others may differ, but if we REFERENCES don’t start debating ecoethics now, the current Bearzi, G. (2009). When swordfish conservation biologists ethical stasis will likely persist. eat swordfish. Conservation Biology, 23, 1–2. • Work hard to humanely bring human popu- Daily, G. C., ed. (1997). Nature’s services: societal depen- lation growth to a halt and start a slow decline. dence on natural ecosystems. Island Press, Washington, • Reduce overconsumption by the already rich DC. while increasing consumption by the needy continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 20. 1 INTRODUCTION 5 Introduction Box 2 (Continued) Ehrlich, P. R. and Ehrlich, A. H. (1981). Extinction: the Leopold, A. (1949). Sand county almanac. Oxford Univer- causes and consequences of the disappearance of spe- sity Press, New York, NY. cies. Random House, New York, NY. Reeves, R. R. (2002). The origins and character of Ehrlich, P. R. and Kennedy, D. (2005). Millennium ‘aboriginal subsistence’ whaling: a global review. assessment of human behavior: a challenge to scientists. Mammal Review, 32, 71–106. Science, 309, 562–563. Singer, P. (1993). Practical ethics. 2nd edn. University Press, Jamieson, D. (2008). Ethics and the environment: an in- Cambridge, UK. troduction. Cambridge University Press, Cambridge, UK. Terborgh, J. (2004). Requiem for nature. Island Press, Washington, DC.kept at a level comprehensible to readers for Saunders. They also examine biophysical aspects ofwhom English is a second language. landscape change, and how such change affects po- The book contains 16 chapters, which are brief- pulations, species, and introduced below: Chapter 6. OverharvestingChapter 1. Conservation biology: past and present Biodiversity is under heavy threat from anthropo-In this chapter, Curt Meine introduces the discipline genic overexploitation (e.g. harvest for food or dec-by tracing its history. He also highlights the inter- oration or of live animals for the pet trade). Fordisciplinary nature of conservation science. example, bushmeat or wild meat hunting is imperil- ing many tropical species as expanding human po-Chapter 2. Biodiversity pulations in these regions seek new sources ofKevin J. Gaston defines biodiversity and lays out the protein and create potentially profitable new ave-obstacles to its better understanding in this chapter. nues for trade at both local and international levels. In this Chapter, Carlos A. Peres highlights the effectsChapter 3. Ecosystem functioning and services of human exploitation of terrestrial and aquaticIn this chapter, Cagan H. Sekercioglu recapitulates biomes on biodiversity.natural ecosystem functions and services. Chapter 7. Invasive speciesChapter 4. Habitat destruction: death by a Daniel Simberloff presents an overview of invasivethousand cuts species, their impacts and management in this chapter.William F. Laurance provides an overview of con-temporary habitat loss in this chapter. He evaluates Chapter 8. Climate changepatterns of habitat destruction geographically and Climate change is quickly emerging as a key issue incontrasts it in different biomes and ecosystems. He the battle to preserve biodiversity. In this chapter,also reviews some of the ultimate and proximate Thomas E. Lovejoy reports on the documented im-factors causing habitat loss. pacts of climate change on biotas.Chapter 5. Habitat fragmentation and landscape Chapter 9. Fire and biodiversitychange Evolutionary and ecological principles related toConceptual approaches used to understand conser- conservation in landscapes subject to regularvation in fragmented landscapes are summarized in fires are presented in this chapter by David M. J. S.this chapter by Andrew F. Bennett and Denis A. Bowman and Brett P. Murphy.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 21. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLChapter 10. Extinctions and the practice of conserving biodiversity in human-modified land-preventing them scapes.Stuart L. Pimm and Clinton N. Jenkins explore why Chapter 14. The roles of people in conservationextinctions are the critical issue for conservation The effective and sustainable protection of biodiver-science. They also list a number of conservation sity will require that the sustenance needs of nativeoptions. people are adequately considered. In this chapter, C.Chapter 11. Conservation planning and priorities Anne Claus, Kai M. A. Chan, and Terre Satterfield highlight that understanding human activities andIn this chapter, Thomas Brooks charts the history, human roles in conservation is fundamental to effec-state, and prospects of conservation planning and tive conservation.prioritization in terrestrial and aquatic habitats. Hefocuses on successful conservation implementation Chapter 15. From conservation theory to practice:planned through the discipline’s conceptual frame- crossing the dividework of vulnerability and irreplaceability. Madhu Rao and Joshua Ginsberg explore the implementation of conservation science in this chap-Chapter 12. Endangered species management: the ter.US experienceIn this chapter, David S. Wilcove focuses on Chapter 16. The conservation biologist’s toolbox –endangered species management, emphasizing the principles for the design and analysis of conserva-United States of America (US) experience. Because tion studiesthe US has one of the oldest and possibly strongest In this chapter, Corey J. A. Bradshaw and Barrylaws to protect endangered species, it provides an W. Brook, discuss measures of biodiversity patternsilluminating case history. followed by an overview of experimental design and associated statistical paradigms. They also presentChapter 13. Conservation in human-modified the analysis of abundance time series, assessmentslandscapes of species’ endangerment, and a brief introductionLian Pin Koh and Toby A. Gardner discuss the to genetic tools to assess the conservation status ofchallenges of conserving biodiversity in degraded species.and modified landscapes with a focus on the tropi- Each chapter includes boxes written by variouscal terrestrial biome in this chapter. They highlight experts describing additional relevant material,the extent to which human activities have modified case studies/success stories, or personal perspec-natural ecosystems and outline opportunities for tives.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 22. 1 CHAPTER 1 Conservation biology: past and present1 Curt MeineOur job is to harmonize the increasing kit of tioners remain embedded within a process ofscientific tools and the increasing recklessness in change that has challenged conservation “in theusing them with the shrinking biotas to which old sense,” even while extending conservation’sthey are applied. In the nature of things we are core commitment to the future of life, human andmediators and moderators, and unless we can non-human, on rewrite the objectives of science we are pre- There is as yet no comprehensive history ofdestined to failure. conservation that allows us to understand the —Aldo Leopold (1940; 1991) causes and context of conservation biology’s emergence. Environmental ethicists and histor-Conservation in the old sense, of this or that ians have provided essential studies of particularresource in isolation from all other resources, is conservation ideas, disciplines, institutions, indi-not enough. Environmental conservation based viduals, ecosystems, landscapes, and resources.on ecological knowledge and social understand- Yet we still lack a broad, fully integrated accounting is required. of the dynamic coevolution of conservation sci- —Raymond Dasmann (1959) ence, philosophy, policy, and practice (MeineConservation biology is a mission-driven disci- 2004). The rise of conservation biology marked apline comprising both pure and applied science. new “rallying point” at the intersection of these. . . We feel that conservation biology is a new domains; exactly how, when, and why it did sofield, or at least a new rallying point for biologists are still questions awaiting exploration.wishing to pool their knowledge and techniquesto solve problems. —Michael E. Soulé and Bruce A. Wilcox (1980) 1.1 Historical foundations of conservation biologyConservation biology, though rooted in older sci- Since conservation biology’s emergence, com-entific, professional, and philosophical traditions, mentary on (and in) the field has rightly empha-gained its contemporary definition only in the sized its departure from prior conservationmid-1980s. Anyone seeking to understand the science and practice. However, the main “thread”history and growth of conservation biology thus of the field—the description, explanation, appre-faces inherent challenges. The field has formed ciation, protection, and perpetuation of biologicaltoo recently to be viewed with historical detach- diversity can be traced much further back throughment, and the trends shaping it are still too fluid the historical tapestry of the biological sciencesto be easily traced. Conservation biology’s practi- and the conservation movement (Mayr 1982; 1 Adapted from Meine, C., Soulé, M., and Noss, R. F. (2006). “A mission‐driven discipline”: the growth of conservation biology.Conservation Biology, 20, 631–651. 7© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 23. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLMcIntosh 1985; Grumbine 1996; Quammen 1996). tions of respect for the natural world both withinThat thread weaves through related themes and and beyond the Western experience (see Box 1.1concepts in conservation, including wilderness and Chapter 14). Long before environmentalismprotection, sustained yield, wildlife protection began to reshape “conservation in the old sense”and management, the diversity-stability hypoth- in the 1960s—prior even to the Progressive Eraesis, ecological restoration, sustainability, and conservation movement of the early 1900s—theecosystem health. By focusing on the thread itself, foundations of conservation biology were beingconservation biology brought the theme of laid over the course of biology’s epic advancesbiological diversity to the fore. over the last four centuries. The “discovery of In so doing, conservation biology has recon- diversity” (to use Ernst Mayr’s phrase) was thenected conservation to deep sources in Western driving force behind the growth of biologicalnatural history and science, and to cultural tradi- thought. “Hardly any aspect of life is more Box 1.1 Traditional ecological knowledge and biodiversity conservation Fikret Berkes Conservation biology is a discipline of Western James Bay, Quebec, Canada (see Box 1.1 science, but there are other traditions of Figure). In the Peruvian Andes, the centre of conservation in various parts of the world (see origin of the potato, the Quetchua people also Chapter 14). These traditions are based on maintain a mosaic of agricultural and natural local and indigenous knowledge and practice. areas as a biocultural heritage site with some Traditional ecological knowledge may be 1200 potato varieties, both cultivated and wild. defined as a cumulative body of knowledge, practice and belief, evolving by adaptive processes and handed down through generations by cultural transmission. It is experiential knowledge closely related to a way of life, multi‐generational, based on oral transmission rather than book learning, and hence different from science in a number of ways. Traditional knowledge does not always result in conservation, just as science does not always result in conservation. But there are a number of ways in which traditional knowledge and practice may lead to conservation outcomes. First, sacred groves and other sacred areas are protected through religious practice and Box 1.1 Figure Paakumshumwaau Biodiversity Reserve in James enforced by social rules. UNESCO’s (the United Bay, Quebec, Canada, established at the request of the Cree Nation Nations Educational, Scientific and Cultural of Wemindji. Photograph by F. Berkes. Organization) World Heritage Sites network In some cases, high biodiversity is explainable includes many sacred sites, such as Machu in terms of traditional livelihood practices that Picchu in Peru. Second, many national parks maintain a diversity of varieties, species and have been established at the sites of former landscapes. For example, Oaxaca State in sacred areas, and are based on the legacy of Mexico exhibits high species richness despite traditional conservation. Alto Fragua Indiwasi the absence of official protected areas. This National Park in Colombia and Kaz Daglari may be attributed to the diversity of local and National Park in Turkey are examples. Third, indigenous practices resulting in multi‐ new protected areas are being established at functional cultural landscapes. In many parts of the request of indigenous peoples as a the world, agroforestry systems that rely on the safeguard against development. One example cultivation of a diversity of crops and trees is the Paakumshumwaau Biodiversity Reserve in together (as opposed to modern continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 24. 1 CONSERVATION BIOLOGY: PAST AND PRESENT 9 Box 1.1 (Continued) monocultures), seem to harbor high species The objective of formal protected areas richness. There are at least three mechanisms is biodiversity conservation, whereas that help conserve biodiversity in the use of traditional conservation is often practiced agroforestry and other traditional practices: for livelihood and cultural reasons. Making biodiversity conservation relevant to most of • Land use regimes that maintain forest the world requires bridging this gap, with an patches at different successional stages con- emphasis on sustainability, equity and a serve biodiversity because each stage repre- diversity of approaches. There is international sents a unique community. At the same time, interest in community‐conserved areas as a such land use contributes to continued ecosys- class of protected areas. Attention to time‐ tem renewal. tested practices of traditional conservation • The creation of patches, gaps and mosaics can help develop a pluralistic, more enhance biodiversity in a given area. In the inclusive definition of conservation, and study of landscape ecology, the principle is that build more robust constituencies for low and intermediate levels of disturbance conservation. often increase biodiversity, as compared to non‐disturbed areas. • Boundaries between ecological zones are characterized by high diversity, and the creation SUGGESTED READING of new edges (ecotones) by disturbance en- Berkes, F. (2008). Sacred ecology, 2nd edn. Routledge, hances biodiversity, but mostly of “edge‐loving” New York, NY. species. Overlaps and mixing of plant and ani- mal species produce dynamic landscapes.characteristic than its almost unlimited diversi- For example, Alfred Russel Wallace (1863) warnedty,” wrote Mayr (1982:133). “Indeed, there is against the “extinction of the numerous forms of lifehardly any biological process or phenomenon which the progress of cultivation invariably en-where diversity is not involved.” tails” and urged his scientific colleagues to assume This “discovery” unfolded as colonialism, the the responsibility for stewardship that came withIndustrial Revolution, human population growth, knowledge of diversity.expansion of capitalist and collectivist economies, The first edition of George Perkins Marsh’sand developing trade networks transformed Man and Nature appeared the following year. Inhuman social, economic, political, and ecological his second chapter, “Transfer, Modification, andrelationships ever more quickly and profoundly Extirpation of Vegetable and of Animal Species,”(e.g. Crosby 1986; Grove 1995; Diamond 1997). Marsh examined the effect of humans on bioticTechnological change accelerated humanity’s ca- diversity. Marsh described human beings as apacity to reshape the world to meet human needs “new geographical force” and surveyed humanand desires. In so doing, it amplified tensions along impacts on “minute organisms,” plants, insects,basic philosophical fault lines: mechanistic/organ- fish, “aquatic animals,” reptiles, birds, andic; utilitarian/reverential; imperialist/arcadian; re- “quadrupeds.” “All nature,” he wrote, “is linkedductionism/holism (Thomas et al. 1956; Worster together by invisible bonds, and every organic1985). As recognition of human environmental im- creature, however low, however feeble, howeverpacts grew, an array of 19th century philosophers, dependent, is necessary to the well-being of somescientists, naturalists, theologians, artists, writers, other among the myriad forms of life with whichand poets began to regard the natural world within the Creator has peopled the earth.” He concludedan expanded sphere of moral concern (Nash 1989). his chapter with the hope that people might© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 25. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL“learn to put a wiser estimate on the works of New concepts from ecology and evolutionarycreation” (Marsh 1864). Through the veil of 19th biology began to filter into conservation and thecentury language, modern conservation biolo- resource management disciplines during the earlygists may recognize Marsh, Wallace, and others 20th century. “Proto-conservation biologists”as common intellectual ancestors. from this period include Henry C. Cowles, Marsh’s landmark volume appeared just as the whose pioneering studies of plant successionpost-Civil War era of rampant resource exploita- and the flora of the Indiana Dunes led him intotion commenced in the United States. A generation active advocacy for their protection (Engel 1983);later, Marsh’s book undergirded the Progressive Victor Shelford, who prodded his fellow ecolo-Era reforms that gave conservation in the United gists to become active in establishing biologicallyStates its modern meaning and turned it into representative nature reserves (Croker 1991); Ar-a national movement. That movement rode thur Tansley, who similarly advocated establish-Theodore Roosevelt’s presidency into public con- ment of nature reserves in Britain, and who insciousness and across the American landscape. 1935 contributed the concept of the “ecosystem”Conservationists in the Progressive Era were fa- to science (McIntosh 1985; Golley 1993); Charlesmously split along utilitarian-preservationist Elton, whose text Animal Ecology (1927) providedlines. The utilitarian Resource Conservation Ethic, the foundations for a more dynamic ecologyrealized within new federal conservation agencies, through his definition of food chains, food webs,was committed to the efficient, scientifically in- trophic levels, the niche, and other basic concepts;formed management of natural resources, to pro- Joseph Grinnell, Paul Errington, Olaus Murie, andvide “the greatest good to the greatest number for other field biologists who challenged prevailingthe longest time” (Pinchot 1910:48). By contrast, the notions on the ecological role and value of preda-Romantic-Transcendental Preservation Ethic, tors (Dunlap 1988); and biologists who sought toovershadowed but persistent through the Progres- place national park management in the USA on asive Era, celebrated the aesthetic and spiritual sound ecological footing (Sellars 1997; Shafervalue of contact with wild nature, and inspired 2001). Importantly, the crisis of the Dust Bowl incampaigns for the protection of parklands, refuges, North America invited similar ecological critiquesforests, and “wild life.” of agricultural practices during the 1930s (Worster Callicott (1990) notes that both ethical camps 1979; Beeman and Pritchard 2001).were “essentially human-centered or ‘anthropo- By the late 1930s an array of conservation con-centric’ . . . (and) regarded human beings or cerns—soil erosion, watershed degradation,human interests as the only legitimate ends and urban pollution, deforestation, depletion of fish-nonhuman natural entities and nature as a whole eries and wildlife populations—brought academ-as means.” Moreover, the science upon which both ic ecologists and resource managers closerrelied had not yet experienced its 20th century re- together and generated a new awareness of con-volutions. Ecology had not yet united the scientific servation’s ecological foundations, in particularunderstanding of the abiotic, plant, and animal the significance of biological diversity. In 1939components of living systems. Evolutionary biolo- Aldo Leopold summarized the point in a speechgy had not yet synthesized knowledge of genetics, to a symbolically appropriate joint meeting of thepopulation biology, and evolutionary biology. Ge- Ecological Society of America and the Society ofology, paleontology, and biogeography were just American Foresters:beginning to provide a coherent narrative of thetemporal dynamics and spatial distribution of life The emergence of ecology has placed theon Earth. Although explicitly informed by the nat- economic biologist in a peculiar dilemma:ural sciences, conservation in the Progressive with one hand he points out the accumu-Era was primarily economic in its orientation, re- lated findings of his search for utility, or lackductionist in its tendencies, and selective in its of utility, in this or that species; with theapplication. other he lifts the veil from a biota© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 26. 1 CONSERVATION BIOLOGY: PAST AND PRESENT 11 so complex, so conditioned by interwoven limnology, marine biology, and biogeography cooperations and competitions, that no man (Mayr 1982). As these advances accrued, main- can say where utility begins or ends. No taining healthy connections between the basic species can be ‘rated’ without the tongue in sciences and their application in resource man- the cheek; the old categories of ‘useful’ and agement fields proved challenging. It fell to a ‘harmful’ have validity only as conditioned diverse cohort of scientific researchers, inter- by time, place, and circumstance. The only preters, and advocates to enter the public policy sure conclusion is that the biota as a whole is fray (including such notable figures as Rachel useful, and (the) biota includes not only Carson, Jacques-Yves Cousteau, Ray Dasmann, plants and animals, but soils and waters as G. Evelyn Hutchinson, Julian Huxley, Eugene well (Leopold 1991:266–67). and Howard Odum, and Sir Peter Scott). Many of these had worldwide influence through theirWith appreciation of “the biota as a whole” came writings and students, their collaborations, andgreater appreciation of the functioning of ecolog- their ecological concepts and methodologies.ical communities and systems (Golley 1993). For Working from within traditional disciplines, gov-Leopold and others, this translated into a redefi- ernment agencies, and academic seats, they stoodnition of conservation’s aims: away from the nar- at the complicated intersection of conservationrow goal of sustaining outputs of discrete science, policy, and practice—a place that wouldcommodities, and toward the more complex come to define conservation biology.goal of sustaining what we now call ecosystem More pragmatically, new federal legislation inhealth and resilience. the USA and a growing body of international As conservation’s aims were thus being rede- agreements expanded the role and responsibilitiesfined, its ethical foundations were being recon- of biologists in conservation. In the USA the Na-sidered. The accumulation of revolutionary tional Environmental Policy Act (1970) requiredbiological insights, combined with a generation’s analysis of environmental impacts in federal deci-experience of fragmented policy, short-term eco- sion-making. The Endangered Species Act (1973)nomics, and environmental decline, yielded Leo- called for an unprecedented degree of scientificpold’s assertion of an Evolutionary-Ecological involvement in the identification, protection, andLand Ethic (Callicott 1990). A land ethic, Leopold recovery of threatened species (see Chapter 12).wrote, “enlarges the boundaries of the communi- Other laws that broadened the role of biologiststy to include soils, waters, plants, and animals, or in conservation and environmental protection in-collectively: the land”; it “changes the role of clude the Marine Mammal Protection Act (1972),Homo sapiens from conqueror of the land-commu- the Clean Water Act (1972), the Forest and Range-nity to plain member and citizen of it” (Leopold land Renewable Resources Planning Act (1974),1949:204). These ethical concepts only slowly the National Forest Management Act (1976), andgained ground in forestry, fisheries management, the Federal Land Policy Management Act (1976).wildlife management, and other resource man- At the international level, the responsibilities ofagement disciplines; indeed, they are contentious biologists were also expanding in response to thestill. adoption of bilateral treaties and multilateral In the years following World War II, as con- agreements, including the UNESCO (United Na-sumer demands increased and technologies tions Educational, Scientific and Cultural Organi-evolved, resource development pressures grew. zation) Man and the Biosphere ProgrammeResource managers responded by expanding (1970), the Convention on International Trade intheir efforts to increase the yields of their particu- Endangered Species of Wild Fauna and Floralar commodities. Meanwhile, the pace of scientific (CITES) (1975), and the Convention on Wetlandschange accelerated in disciplines across the of International Importance (the “Ramsar Con-biological spectrum, from microbiology, genetics, vention”) (1975). In 1966 the International Unionsystematics, and population biology to ecology, for the Conservation of Nature (IUCN) published© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 27. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLit first “red list” inventories of threatened species. work”. Constructing that “firm scientific basis”In short, the need for rigorous science input into required—and attracted—researchers and practi-conservation decision-making was increasing, tioners from varied disciplines (including Ehren-even as the science of conservation was changing. feld himself, whose professional background wasThis state of affairs challenged the traditional in medicine and physiological ecology). The com-orientation of resource managers and research mon concern that transcended the disciplinarybiologists alike. boundaries was biological diversity: its extent, role, value, and fate. By the mid-1970s, the recurring debates within theoretical ecology over the relationship between1.2 Establishing a new interdisciplinary species diversity and ecosystem stability werefield intensifying (Pimm 1991; Golley 1993; McCannIn the opening chapter of Conservation Biology: An 2000). Among conservationists the theme of di-Evolutionary-Ecological Perspective, editors Michael versity, in eclipse since Leopold’s day, began toSoulé and Bruce Wilcox (1980) described conser- re-emerge. In 1951, renegade ecologists had cre-vation biology as “a mission-oriented discipline ated The Nature Conservancy for the purpose ofcomprising both pure and applied science.” The protecting threatened sites of special biologicalphrase crisis-oriented (or crisis-driven) was soon and ecological value. In the 1960s voices for di-added to the list of modifiers describing the versity began to be heard within the traditionalemerging field (Soulé 1985). This characterization conservation fields. Ray Dasmann, in A Differentof conservation biology as a mission-oriented, Kind of Country (1968: vii) lamented “the prevail-crisis-driven, problem-solving field resonates with ing trend toward uniformity” and made the caseechoes of the past. The history of conservation “for the preservation of natural diversity” and forand environmental management demonstrates cultural diversity as well. Pimlott (1969) detectedthat the emergence of problem-solving fields (or “a sudden stirring of interest in diversity . . . Notnew emphases within established fields) invari- until this decade did the word diversity, as anably involves new interdisciplinary connections, ecological and genetic concept, begin to enter thenew institutions, new research programs, and vocabulary of the wildlife manager or land-usenew practices. Conservation biology would fol- planner.” Hickey (1974) argued that wildlife ecol-low this pattern in the 1970s, 1980s, and 1990s. ogists and managers should concern themselves In 1970 David Ehrenfeld published Biological with “all living things”; that “a scientificallyConservation, an early text in a series of publications sound wildlife conservation program” shouldthat altered the scope, content, and direction of “encompass the wide spectrum from one-celledconservation science (e.g. MacArthur and Wilson plants and animals to the complex species we call1963; MacArthur and Wilson 1967; MacArthur birds and mammals.” Conservation scientists and1972; Soulé and Wilcox 1980; CEQ 1980; Frankel advocates of varied backgrounds increasinglyand Soulé 1981; Schonewald-Cox et al. 1983; Harris framed the fundamental conservation problem1984; Caughley and Gunn 1986; Soulé 1986; Soulé in these new and broader terms (Farnham 2002).1987a) (The journal Biological Conservation had also As the theme of biological diversity gainedbegun publication a year earlier in England). In his traction among conservationists in the 1970s, thepreface Ehrenfeld stated, “Biologists are beginning key components of conservation biology began toto forge a discipline in that turbulent and vital area coalesce around it:where biology meets the social sciences and huma-nities”. Ehrenfeld recognized that the “acts of con-servationists are often motivated by strongly · Within the sciences proper, the synthesis of knowledge from island biogeography and popula-humanistic principles,” but cautioned that “the tion biology greatly expanded understanding of thepractice of conservation must also have a firm distribution of species diversity and the phenomenascientific basis or, plainly stated, it is not likely to of speciation and extinction.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 28. 1 CONSERVATION BIOLOGY: PAST AND PRESENT 13· The fate of threatened species (both in situ andex situ) and the loss of rare breeds and plant germ- Evolution) (Frankel and Soulé 1981). Soulé’s work on that volume led to the convening of the Firstplasm stimulated interest in the heretofore neglected International Conference on Conservation Biology(and occasionally even denigrated) application of in September 1978. The meeting brought togethergenetics in conservation. what looked from the outside like “an odd assort-· Driven in part by the IUCN red listing process,captive breeding programs grew; zoos, aquaria, and ment of academics, zoo-keepers, and wildlife con- servationists” (Gibbons 1992). Inside, however,botanical gardens expanded and redefined their role the experience was more personal, among indivi-as partners in conservation. duals who had come together through important,· Wildlife ecologists, community ecologists, andlimnologists were gaining greater insight into the and often very personal, shifts in professional prio- rities. The proceedings of the 1978 conference wererole of keystone species and top-down interactions published as Conservation Biology: An Evolutionary-in maintaining species diversity and ecosystem Ecological Perspective (Soulé and Wilcox 1980). Thehealth. conference and the book initiated a series of meet-· Within forestry, wildlife management, rangemanagement, fisheries management, and other ap- ings and proceedings that defined the field for its growing number of participants, as well as forplied disciplines, ecological approaches to resource those outside the immediate circle (Brussardmanagement gained more advocates. 1985; Gibbons 1992).· Advances in ecosystem ecology, landscape ecolo-gy, and remote sensing provided increasingly so- Attention to the genetic dimension of conserva- tion continued to gain momentum into the earlyphisticated concepts and tools for land use and 1980s (Schonewald-Cox et al. 1983). Meanwhile,conservation planning at larger spatial scales. awareness of threats to species diversity and causes· As awareness of conservation’s social dimensionsincreased, discussion of the role of values in science of extinction was reaching a broader professional and public audience (e.g. Ziswiler 1967; Iltis 1972;became explicit. Interdisciplinary inquiry gave rise to Terborgh 1974; Ehrlich and Ehrlich 1981). In partic-environmental history, environmental ethics, ecolog- ular, the impact of international development po-ical economics, and other hybrid fields. licies on the world’s species-rich, humid tropical forests was emerging as a global concern. Field As these trends unfolded, “keystone indivi- biologists, ecologists, and taxonomists, alarmedduals” also had special impact. Peter Raven and by the rapid conversion of the rainforests—andPaul Ehrlich (to name two) made fundamental witnesses themselves to the loss of research sitescontributions to coevolution and population and study organisms—began to sound alarms (e.g.biology in the 1960s before becoming leading Gómez-Pompa et al. 1972; Janzen 1972). By theproponents of conservation biology. Michael early 1980s, the issue of rainforest destruction wasSoulé, a central figure in the emergence of conser- highlighted through a surge of books, articles, andvation biology, recalls that Ehrlich encouraged scientific reports (e.g. Myers 1979, 1980; NAS 1980;his students to speculate across disciplines, and NRC 1982; see also Chapter 4).had his students read Thomas Kuhn’s The Struc- During these years, recognition of the needs ofture of Scientific Revolutions (1962). The intellectual the world’s poor and the developing world wassyntheses in population biology led Soulé to adopt prompting new approaches to integrating conser-(around 1976) the term conservation biology for his vation and development. This movement wasown synthesizing efforts. embodied in a series of international programs, For Soulé, that integration especially entailed meetings, and reports, including the Man and thethe merging of genetics and conservation (Soulé Biosphere Programme (1970), the United Nations1980). In 1974 Soulé visited Sir Otto Frankel while Conference on the Human Environment held inon sabbatical in Australia. Frankel approached Stockholm (1972), and the World ConservationSoulé with the idea of collaborating on a volume Strategy (IUCN 1980). These approaches eventu-on the theme (later published as Conservation and ally came together under the banner of sustainable© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 29. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLdevelopment, especially as defined in the report of resource management agencies, and internationalthe World Commission on Environment and De- development organizations (Soulé 1987b).velopment (the “Brundtland Report”) (WCED In retrospect, the rapid growth of conservation1987). The complex relationship between devel- biology reflected essential qualities that set itopment and conservation created tensions within apart from predecessor and affiliated fields:conservation biology from the outset, but alsodrove the search for deeper consensus and inno-vation (Meine 2004). · Conservation biology rests upon a scientific foun- dation in systematics, genetics, ecology, and evolu- A Second International Conference on Conser- tionary biology. As the Modern Synthesisvation Biology convened at the University of Mi- rearranged the building blocks of biology, and newchigan in May 1985 (Soulé 1986). Prior to the insights emerged from population genetics, devel-meeting, the organizers formed two committees opmental genetics (heritability studies), and islandto consider establishing a new professional socie- biogeography in the 1960s, the application ofty and a new journal. A motion to organize the biology in conservation was bound to shift as well.Society for Conservation Biology (SCB) was ap- This found expression in conservation biology’s pri-proved at the end of the meeting (Soulé 1987b). mary focus on the conservation of genetic, species,One of the Society’s first acts was to appoint and ecosystem diversity (rather than those ecosys-David Ehrenfeld editor of the new journal Conser- tem components with obvious or direct economicvation Biology (Ehrenfeld 2000). value). The founding of SCB coincided with planningfor the National Forum on BioDiversity, held · Conservation biology paid attention to the entire biota; to diversity at all levels of biological organiza-September 21–24, 1986 in Washington, DC. The tion; to patterns of diversity at various temporal andforum, broadcast via satellite to a national spatial scales; and to the evolutionary and ecologicaland international audience, was organized by processes that maintain diversity. In particular,the US National Academy of Sciences and emerging insights from ecosystem ecology, distur-the Smithsonian Institution. Although arranged bance ecology, and landscape ecology in the 1980sindependently of the process that led to SCB’s shifted the perspective of ecologists and conserva-creation, the forum represented a convergence tionists, placing greater emphasis on the dynamicof conservation concern, scientific expertise, and nature of ecosystems and landscapes (e.g. Pickettinterdisciplinary commitment. In planning the and White 1985; Forman 1995).event, Walter Rosen, a program officer with theNational Research Council, began using a con- · Conservation biology was an interdisciplinary, systems-oriented, and inclusive response to conser-tracted form of the phrase biological diversity. The vation dilemmas exacerbated by approaches thatabridged form biodiversity began its etymological were too narrowly focused, fragmented, and exclu-career. sive (Soulé 1985; Noss and Cooperrider 1994). The forum’s proceedings were published as Bio- It provided an interdisciplinary home for those indiversity (Wilson and Peter 1988). The wide impact established disciplines who sought new ways to or-of the forum and the book assured that the land- ganize and use scientific information, and who fol-scape of conservation science, policy, and action lowed broader ethical imperatives. It also reachedwould never be the same. For some, conservation beyond its own core scientific disciplines to incorpo-biology appeared as a new, unproven, and unwel- rate insights from the social sciences and humanities,come kid on the conservation block. Its adherents, from the empirical experience of resource managers,however, saw it as the culmination of trends long and from diverse cultural sources (Grumbine 1992;latent within ecology and conservation, and as a Knight and Bates 1995).necessary adaptation to new knowledge and agathering crisis. Conservation biology quickly · Conservation biology acknowledged its status as an inherently “value-laden” field. Soulé (1985) as-gained its footing within academia, zoos and bo- serted that “ethical norms are a genuine part oftanical gardens, non-profit conservation groups, conservation biology.” Noss (1999) regarded this as© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 30. 1 CONSERVATION BIOLOGY: PAST AND PRESENT 15a distinguishing characteristic, noting an “overarch- funding priorities and encouraged those interest-ing normative assumption in conservation bio- ed in the new field. A steady agenda of confer-logy . . . that biodiversity is good and ought to be ences on biodiversity conservation broughtpreserved.” Leopold’s land ethic and related appeals together academics, agency officials, resourceto intergenerational responsibilities and the intrinsic managers, business representatives, internationalvalue of non-human life motivated growing numbers aid agencies, and non-governmental organiza-of conservation scientists and environmental ethicists tions. In remarkably rapid order, conservation(Ehrenfeld 1981; Samson and Knopf 1982; Devall and biology gained legitimacy and secured a profes-Sessions 1985; Nash 1989). This explicit recognition sional foothold.of conservation biology’s ethical content stood Not, however, without resistance, skepticism,in contrast to the usual avoidance of such considera- and occasional ridicule. As the field grew, com-tions within the sciences historically (McIntosh 1980; plaints came from various quarters. ConservationBarbour 1995; Barry and Oelschlaeger 1996). biology was caricatured as a passing fad, a re-· Conservation biology recognized a “close link-age” between biodiversity conservation and eco- sponse to trendy environmental ideas (and mo- mentarily available funds). Its detractors regardednomic development and sought new ways to it as too theoretical, amorphous, and eclectic; tooimprove that relationship. As sustainability became promiscuously interdisciplinary; too enamored ofthe catch-all term for development that sought to models; and too technique-deficient and data-poorblend environmental, social, and economic goals, to have any practical application (Gibbons 1992).conservation biology provided a new venue at the Conservation biologists in North America wereintersection of ecology, ethics, and economics (Daly accused of being indifferent to the conservationand Cobb 1989). To achieve its goals, conservation traditions of other nations and regions. Some sawbiology had to reach beyond the sciences and gener- conservation biology as merely putting “old wineate conversations with economists, advocates, poli- in a new bottle” and dismissing the rich experiencecy-makers, ethicists, educators, the private sector, of foresters, wildlife managers, and other resourceand community-based conservationists. managers (Teer 1988; Jensen and Krausman 1993). Biodiversity itself was just too broad, or confusing, Conservation biology thus emerged in response or “thorny” a term (Udall 1991; Takacs 1996).to both increasing knowledge and expanding Such complaints made headlines within thedemands. In harnessing that knowledge and scientific journals and reflected real tensionsmeeting those demands, it offered a new, within resource agencies, academic departments,integrative, and interdisciplinary approach to and conservation organizations. Conservation bi-conservation science. ology had indeed challenged prevalent para- digms, and such responses were to be expected. Defending the new field, Ehrenfeld (1992: 1625)1.3 Consolidation: conservation biology wrote, “Conservation biology is not defined by asecures its niche discipline but by its goal—to halt or repair theIn June 1987 more than 200 people attended the undeniable, massive damage that is being done tofirst annual meeting of the Society for Conserva- ecosystems, species, and the relationships of hu-tion Biology in Bozeman, Montana, USA. The mans to the environment. . . . Many specialists in arapid growth of the new organization’s member- host of fields find it difficult, even hypocritical, toship served as an index to the expansion of the continue business as usual, blinders firmly infield generally. SCB tapped into the burgeoning place, in a world that is falling apart.”interest in interdisciplinary conservation science Meanwhile, a spate of new and complex con-among younger students, faculty, and conserva- servation issues were drawing increased attentiontion practitioners. Universities established new to biodiversity conservation. In North America,courses, seminars, and graduate programs. Scien- the Northern Spotted Owl (Strix occidentalis caur-tific organizations and foundations adjusted their ina) became the poster creature in deeply© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 31. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLcontentious debates over the fate of remaining Amid the flush of excitement in establishingold-growth forests and alternative approaches to conservation biology, it was sometimes easy toforest management; the Exxon Valdez oil spill and overlook the challenges inherent in the effort.its aftermath put pollution threats and energy Ehrenfeld (2000) noted that the nascent field waspolicies on the front page; the anti-environmental, “controversy-rich.” Friction was inherent notanti-regulatory “Wise Use” movement gained in only in conservation biology’s relationship topolitical power and influence; arguments over related fields, but within the field itself. Some oflivestock grazing practices and federal rangeland this was simply a result of high energy applied topolicies pitted environmentalists against ran- a new endeavor. Often, however, this reflectedchers; perennial attempts to allow oil develop- deeper tensions in conservation: between sustain-ment within the Arctic National Wildlife Refuge able use and protection; between public and pri-continued; and moratoria were placed on com- vate resources; between the immediate needs ofmercial fishing of depleted stocks of northern people, and obligations to future generations andcod (Alverson et al. 1994; Yaffee 1994; Myers other life forms. Conservation biology would beet al. 1997; Knight et al. 2002; Jacobs 2003). the latest stage on which these long-standing ten- At the international level, attention focused on sions would express themselves.the discovery of the hole in the stratospheric Other tensions reflected the special role thatozone layer over Antarctica; the growing scien- conservation biology carved out for itself.tific consensus about the threat of global warm- Conservation biology was largely a product ofing (the Intergovernmental Panel on Climate American institutions and individuals, yet soughtChange was formed in 1988 and issued its first to address a problem of global proportions (Meffeassessment report in 1990); the environmental 2002). Effective biodiversity conservation en-legacy of communism in the former Soviet bloc; tailed work at scales from the global to the local,and the environmental impacts of international and on levels from the genetic to the species to theaid and development programs. In 1992, 172 na- community; yet actions at these different scalestions gathered in Rio de Janeiro at the United and levels required different types of informa-Nations Conference on Environment and Devel- tion, skills, and partnerships (Noss 1990). Profes-opment (the “Earth Summit”). Among the pro- sionals in the new field had to be firmly groundedducts of the summit was the Convention on within particular professional specialties, yet con-Biological Diversity. In a few short years, the versant across disciplines (Trombulak 1994; Nossscope of biodiversity conservation, science, and 1997). Success in the practice of biodiversity con-policy had expanded dramatically (e.g. McNeely servation was measured by on-the-ground im-et al. 1990; Lubchenco et al. 1991). pact, yet the science of conservation biology was To some degree, conservation biology had de- obliged (as are all sciences) to undertake rigorousfined its own niche by synthesizing scientific dis- research and to define uncertainty (Noss 2000).ciplines, proclaiming its special mission, and Conservation biology was a “value-laden” fieldgathering together a core group of leading scien- adhering to explicit ethical norms, yet sought totists, students, and conservation practitioners. advance conservation through careful scientificHowever, the field was also filling a niche that analysis (Barry and Oelschlager 1996). These ten-was rapidly opening around it. It provided a sions within conservation biology were present atmeeting ground for those with converging inter- birth. They continue to present importantests in the conservation of biological diversity. It challenges to conservation biologists. They alsowas not alone in gaining ground for interdisci- give the field its creativity and vitality.plinary conservation research and practice. Itjoined restoration ecology, landscape ecology, ag- 1.4 Years of growth and evolutionroecology, ecological economics, and other newfields in seeking solutions across traditional aca- Although conservation biology has been andemic and intellectual boundaries. organized field only since the mid-1980s, it is© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 32. 1 CONSERVATION BIOLOGY: PAST AND PRESENT 17possible to identify and summarize at least sever- Even as conservation biologists have honedal salient trends that have shaped it since. tools for designing protected area networks and managing protected areas more effectively (see Chapter 11), they have looked beyond reserve1.4.1 Implementation and transformation boundary lines to the matrix of surroundingConservation biologists now work in a much lands (Knight and Landres 1998). Conservationmore elaborate field than existed at the time of biologists play increasingly important roles inits founding. Much of the early energy—and de- defining the biodiversity values of aquatic eco-bate—in conservation biology focused on ques- systems, private lands, and agroecosystems. Thetions of the genetics and demographics of small result is much greater attention to private landpopulations, population and habitat viability, conservation, more research and demonstrationlandscape fragmentation, reserve design, and at the interface of agriculture and biodiversitymanagement of natural areas and endangered conservation, and a growing watershed- andspecies. These topics remain close to the core of community-based conservation movement. Con-conservation biology, but the field has grown servation biologists are now active across thearound them. Conservation biologists now tend entire landscape continuum, from wildlands toto work more flexibly, at varied scales and in agricultural lands and from suburbs to cities,varied ways. In recent years, for example, more where conservation planning now meets urbanattention has focused on landscape permeability design and green infrastructure mapping (e.g.and connectivity, the role of strongly interacting Wang and Moskovits 2001; CNT and Openlandsspecies in top-down ecosystem regulation, and Project 2004).the impacts of global warming on biodiversity(Hudson 1991; Lovejoy and Peters 1994; Soulé 1.4.2 Adoption and integrationand Terborgh 1999; Ripple and Beschta 2005;Pringle et al. 2007; Pringle 2008; see Chapters 5 Since the emergence of conservation biology, theand 8). conceptual boundaries between it and other Innovative techniques and technologies (such fields have become increasingly porous. Re-as computer modeling and geographic informa- searchers and practitioners from other fieldstion systems) have obviously played an impor- have come into conservation biology’s circle,tant role in the growth of conservation biology. adopting and applying its core concepts whileThe most revolutionary changes, however, have contributing in turn to its further development.involved the reconceptualizing of science’s role in Botanists, ecosystem ecologists, marine biolo-conservation. The principles of conservation biol- gists, and agricultural scientists (among otherogy have spawned creative applications among groups) were underrepresented in the field’sconservation visionaries, practitioners, planners, early years. The role of the social sciences in con-and policy-makers (Noss et al. 1997; Adams 2005). servation biology has also expanded within theTo safeguard biological diversity, larger-scale field (Mascia et al. 2003). Meanwhile, conserva-and longer-term thinking and planning had to tion biology’s concepts, approaches, and findingstake hold. It has done so under many rubrics, have filtered into other fields. This “permeation”including: adaptation of the biosphere reserve (Noss 1999) is reflected in the number of biodi-concept (Batisse 1986); the development of gap versity conservation-related articles appearing inanalysis (Scott et al. 1993); the movement toward the general science journals such as Science andecosystem management and adaptive manage- Nature, and in more specialized ecological andment (Grumbine 1994b; Salafsky et al. 2001; resource management journals. Since 1986 sever-Meffe et al. 2002); ecoregional planning and anal- al new journals with related content have ap-ogous efforts at other scales (Redford et al. 2003); peared, including Ecological Applications (1991),and the establishment of marine protected areas the Journal of Applied Ecology (1998), the on-lineand networks (Roberts et al. 2001). journal Conservation Ecology (1997) (now called© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 33. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLEcology and Society), Frontiers in Ecology and the Blue Ocean Institute, and the Pew Institute forEnvironment (2003), and Conservation Letters Ocean Science.(2008). Interest in freshwater conservation biology has The influence of conservation biology is even also increased as intensified human demandsmore broadly evident in environmental design, continue to affect water quality, quantity, distri-planning, and decision-making. Conservation bution, and use. Conservationists have come tobiologists are now routinely involved in land-use appreciate even more deeply the essential hydro-and urban planning, ecological design, landscape logical connections between groundwater, sur-architecture, and agriculture (e.g. Soulé 1991; Nas- face waters, and atmospheric waters, and thesauer 1997; Babbitt 1999; Jackson and Jackson impact of human land use on the health and2002; Miller and Hobbs 2002; Imhoff and Carra biological diversity of aquatic ecosystems (Leo-2003; Orr 2004). Conservation biology has spurred pold 1990; Baron et al. 2002; Glennon 2002; Huntactivity within such emerging areas of interest as and Wilcox 2003; Postel and Richter 2003). Con-conservation psychology (Saunders 2003) and servation biologists have become vital partnersconservation medicine (Grifo and Rosenthal in interdisciplinary efforts, often at the water-1997; Pokras et al. 1997; Tabor et al. 2001; Aguirre shed level, to steward freshwater as both anet al. 2002). Lidicker (1998) noted that “conserva- essential ecosystem component and a basiction needs conservation biologists for sure, but it human need.also needs conservation sociologists, conservationpolitical scientists, conservation chemists, conser- 1.4.4 Building capacityvation economists, conservation psychologists,and conservation humanitarians.” Conservation At the time of its founding, conservation biologybiology has helped to meet this need by catalyzing was little known beyond the core group of scien-communication and action among colleagues tists and conservationists who had created it.across a wide spectrum of disciplines. Now the field is broadly accepted and well repre- sented as a distinct body of interdisciplinary knowledge worldwide. Several textbooks ap- peared soon after conservation biology gained1.4.3 Marine and freshwater conservation its footing (Primack 1993; Meffe and Carrollbiology 1994; Hunter 1996). These are now into their sec-Conservation biology’s “permeation” has been ond and third editions. Additional textbooksespecially notable with regard to aquatic ecosys- have been published in more specialized subjecttems and marine environments. In response to areas, including insect conservation biologylong-standing concerns over “maximum sus- (Samways 1994), conservation of plant biodiver-tained yield” fisheries management, protection sity (Frankel et al. 1995), forest biodiversityof marine mammals, depletion of salmon stocks, (Hunter and Seymour 1999), conservation genet-degradation of coral reef systems, and other is- ics (Frankham et al. 2002), marine conservationsues, marine conservation biology has emerged biology (Norse and Crowder 2005), and tropicalas a distinct focus area (Norse 1993; Boersma conservation biology (Sodhi et al. 2007).1996; Bohnsack and Ault 1996; Safina 1998; Academic training programs in conservationThorne-Miller 1998; Norse and Crowder 2005). biology have expanded and now exist around theThe application of conservation biology in marine world (Jacobson 1990; Jacobson et al. 1995; Rodrí-environments has been pursued by a number of guez et al. 2005). The interdisciplinary skills ofnon-governmental organizations, including conservation biologists have found acceptanceSCB’s Marine Section, the Ocean Conservancy, within universities, agencies, non-governmentalthe Marine Conservation Biology Institute, the organizations, and the private sector. FundersCenter for Marine Biodiversity and Conservation have likewise helped build conservation biology’sat the Scripps Institution of Oceanography, the capacity through support for students, academic© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 34. 1 CONSERVATION BIOLOGY: PAST AND PRESENT 19programs, and basic research and field projects. scientific roots of biodiversity conservation areDespite such growth, most conservation biologists obviously not limited to one nation or continentwould likely agree that the capacity does not near- (see Box 1.2). Although the international conser-ly meet the need, given the urgent problems in vation movement dates back more than a centu-biodiversity conservation. Even the existing sup- ry, the history of the science from an internationalport is highly vulnerable to budget cutbacks, perspective has been inadequately studied (Blan-changing priorities, and political pressures. din 2004). This has occasionally led to healthy debate over the origins and development of con- servation biology. Such debates, however, have1.4.5 Internationalization not hindered the trend toward greater interna-Conservation biology has greatly expanded its tional collaboration and representation withininternational reach (Meffe 2002; Meffe 2003). The the field (e.g. Medellín 1998). Box 1.2 Conservation in the Philippines Mary Rose C. Posa Conservation biology has been referred to as a a burgeoning human population. The “discipline with a deadline” (Wilson 2000). As Philippines has thus been pegged as a top the rapid loss and degradation of ecosystems conservation “hotspot” for terrestrial and accelerates across the globe, some scientists marine ecosystems, and there are fears that it suggest a strategy of triage—in effect, writing could be the site of the first major extinction off countries that are beyond help (Terborgh spasm (Heaney and Mittermeier 1997; Myers 1999). But are there any truly lost causes in et al. 2000; Roberts et al. 2002). Remarkably, conservation? and despite this precarious situation, there is The Philippines is a mega‐biodiversity evidence that hope exists for biodiversity country with exceptionally high levels of conservation in the Philippines. endemism (~50% of terrestrial vertebrates and Indication of the growing valuation of 45–60% of vascular plants; Heaney and biodiversity, sustainable development and Mittermeier 1997). However, centuries of environmental protection can be seen in exploitation and negligence have pushed its different sectors of Philippine society. Stirrings ecosystems to their limit, reducing primary of grassroots environmental consciousness forest cover [less than 3% remaining; FAO began in the 1970s, when marginalized (Food and Agriculture Organization of the communities actively opposed unsustainable United Nations) 2005], decimating mangroves commercial developments, blocking logging (90% lost; Primavera 2000), and severely trucks, and protesting the construction of large damaging coral reefs (~5% retaining 75–100% dams (Broad and Cavanagh 1993). After the live cover; Gomez et al. 1994), leading to a high 1986 overthrow of dictator Ferdinand Marcos, number of species at risk of extinction [~21% of a revived democracy fostered the emergence of vertebrates assessed; IUCN (International Union civil society groups focused on environmental for Conservation of Nature and Natural issues. The devolution of authority over natural Resources) 2006]. Environmental degradation resources from central to local governments has also brought the loss of soil fertility, also empowered communities to create and pollution, and diminished fisheries enforce regulations on the use of local productivity, affecting the livelihood of millions resources. There are now laudable examples of rural inhabitants. Efforts to preserve where efforts by communities and non‐ biodiversity and implement sound governmental organizations (NGOs) have environmental policies are hampered by made direct impacts on conserving endangered entrenched corruption, weak governance and species and habitats (Posa et al. 2008). opposition by small but powerful interest Driven in part by public advocacy, there has groups. In addition, remaining natural also been considerable progress in resources are under tremendous pressure from environmental legislation. In particular, the continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 35. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL Box 1.2 (Continued) National Integrated Protected Areas System Act complacency, that positive progress has been provides for stakeholder involvement in made in the Philippines—a conservation “worst protected area management, which has been a case scenario”—suggests that there are key element of success for various reserves. grounds for optimism for biodiversity Perhaps the best examples of where people‐ conservation in tropical countries worldwide. centered resource use and conservation have come together are marine protected areas (MPAs) managed by coastal communities across REFERENCES the country—a survey of 156 MPAs reported that 44.2% had good to excellent management Alcala, A. C. and Russ, G. R. (2006). No‐take marine (Alcala and Russ 2006). reserves and reef fisheries management in the Philip- pines: a new people power revolution. Ambio, 35, Last, but not least, there has been renewed interest in biodiversity research in academia, 245–254. increasing the amount and quality of Broad, R. and Cavanagh, J. (1993). Plundering paradise: the struggle for the environment in the Philippines. biodiversity information (see Box 1.2 Figure). Labors of field researchers result in hundreds of University of California Press, Berkeley, CA. additional species yet to be described, and Dutson, G. C. L., Magsalay, P. M., and Timmins, R. J. (1993). some rediscoveries of species thought to be The rediscovery of the Cebu Flowerpecker Dicaeum quadricolor, with notes on other forest birds on Cebu, extinct (e.g. Cebu flowerpecker Dicaeum quadricolor; Dutson et al. 1993). There are Philippines. Bird Conservation International, 3, 235–243. increasing synergies and networks among FAO (Food and Agriculture Organization of the United Nations) (2005). Global forest resources assessment conservation workers, politicians, community leaders, park rangers, researchers, local people, 2005, Country report 202: Philippines. Forestry and international NGOs, as seen from the Department, FAO, Rome, Italy. Gomez, E. D., Aliño, P. M., Yap, H. T., Licuanan, W. Y. growth of the Wildlife Conservation Society of the Philippines, which has a diverse (1994). A review of the status of Philippine reefs. Marine membership from all these sectors. Pollution Bulletin, 29, 62–68. Heaney, L. and Mittermeier, R. A. (1997). The Philippines. 140 In R. A. Mittermeier, G. P. Robles, and C. G. Mittermeier, eds Megadiversity: earth’s biologically wealthiest 120 nations, pp. 236–255. CEMEX, Monterrey, Mexico. Number of publications 100 IUCN (International Union for Conservation of Nature and 80 Natural Resources) (2006). 2006 IUCN Red List of threatened species. 60 Myers, N., Mittermeier, R. A., Mittermeier, C. G., da Fonseca, 40 G. A. B., and Kent, J. (2000). Biodiversity hotspots for conservation priorities. Nature, 403, 853–858. 20 Posa, M. R. C., Diesmos, A. C., Sodhi, N. S., and Brooks, 0 T. M. (2008). Hope for threatened biodiversity: lessons from the Philippines. BioScience, 58, 231–240. 1980 1985 1990 1995 2000 2005 Primavera, J. H. (2000). Development and conservation of Year Philippine mangroves: Institutional issues. Ecological Box 1.2 Figure Steady increase in the number of publications on Economics, 35, 91–106. Philippine biodiversity and conservation, obtained from searching Roberts, C. M., McClean, C. J., Veron, J. E. N., et al. (2002). three ISI Web of Knowledge databases for the period 1980–2007. Marine biodiversity hotspots and conservation priorities for tropical reefs. Science, 295, 1280–1284. While many daunting challenges remain Terborgh, J. (1999). Requiem for nature. Island Press, especially in the area of conservation of Washington, DC. populations (Chapter 10) and ecosystems Wilson, E. O. (2000). On the future of conservation biology. services (Chapter 3), and there is no room for Conservation Biology, 14, 1–3.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 36. 1 CONSERVATION BIOLOGY: PAST AND PRESENT 21 This growth is reflected in the expanding institu- 1.5 Conservation biology: a worktional and membership base of the Society for in progressConservation Biology. The need to reach across These trends (and no doubt others) raise impor-national boundaries was recognized by the foun- tant questions for the future. Conservation biolo-ders of the SCB. From its initial issue Conservation gy has grown quickly in a few brief decades, yetBiology included Spanish translations of article ab- most conservation biologists would assert thatstracts. The Society has diversified its editorial growth for growth’s sake is hardly justified. Asboard, recognized the accomplishments of leading disciplines and organizations become moreconservation biologists from around the world, structured, they are liable to equate mere expan-and regularly convened its meetings outside the sion with progress in meeting their missions (Eh-USA. A significant move toward greater interna- renfeld 2000). Can conservation biology sustaintional participation in the SCB came when, in 2000, its own creativity, freshness, and vision? In itsthe SCB began to develop its regional sections. collective research agenda, is the field asking, and answering, the appropriate questions? Is it performing its core function—providing reliable1.4.6 Seeking a policy voice and useful scientific information on biological diversity and its conservation—in the most effec-Conservation biology has long sought to define tive manner possible? Is that information makingan appropriate and effective role for itself in shap- a difference? What “constituencies” need to being public policy (Grumbine 1994a). Most who more fully involved and engaged?call themselves conservation biologists feel obli- While continuing to ponder such questions, con-gated to be advocates for biodiversity (Oden- servation biologists cannot claim to have turnedbaugh 2003). How that obligation ought to be back the threats to life’s diversity. Yet the fieldfulfilled has been a source of continuing debate has contributed essential knowledge at a timewithin the field. Some scientists are wary of play- when those threats have continued to mount. Iting an active advocacy or policy role, lest their has focused attention on the full spectrum ofobjectivity be called into question. Conversely, biological diversity, on the ecological processesbiodiversity advocates have responded to the ef- that maintain it, on the ways we value it, and onfect that “if you don’t use your science to shape steps that can be taken to conserve it. It has broughtpolicy, we will.” scientific knowledge, long-range perspectives, and Conservation biology’s inherent mix of science a conservation ethic into the public and profession-and ethics all but invited such debate. Far from al arenas in new ways. It has organized scientificavoiding controversy, Conservation Biology’s information to inform decisions affecting biodiver-founding editor David Ehrenfeld built dialogue sity at all levels and scales. In so doing, it hason conservation issues and policy into the journal helped to reframe fundamentally the relationshipat the outset. Conservation Biology has regularly between conservation philosophy, science, andpublished letters and editorials on the question of practice.values, advocacy, and the role of science in shapingpolicy. Conservation biologists have not achievedfinal resolution on the matter. Perhaps in the end itis irresolvable, a matter of personal judgment in- Summaryvolving a mixture of scientific confidence levels,uncertainty, and individual conscience and re-sponsibility. “Responsibility” is the key word, as · Conservation biology emerged in the mid-1980s as a new field focused on understanding, protecting,all parties to the debate seem to agree that advoca- and perpetuating biological diversity at all scalescy, to be responsible, must rest on a foundation of and all levels of biological organization.solid science and must be undertaken with honestyand integrity (Noss 1999). · Conservation biology has deep roots in the growth of biology over several centuries, but its© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 37. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLemergence reflects more recent developments in an Alverson, W. S., Kuhlman, W., and Waller, D. M. (1994).array of biological sciences (ecology, genetics, evo- Wild forests: conservation biology and public policy. Islandlutionary biology, etc.) and natural resource man- Press, Washington, DC.agement fields (forestry, wildlife and fisheries Babbitt, B. (1999). Noah’s mandate and the birth of urban bioplanning. Conservation Biology, 13, 677–, etc.).· Conservation biology was conceived as a “mis-sion-oriented” field based in the biological sciences, Barbour, M. G. (1995). Ecological fragmentation in the Fifties. In W. Cronon, ed. Uncommon ground: toward reinventing nature, pp. 233–255. W. W. Norton, New York.but with an explicit interdisciplinary approach that Baron, J. S., Poff, N. L., Angermeier, P. L., et al. (2002).incorporated insights from the social sciences, hu- Meeting ecological and societal needs for freshwater.manities, and ethics. Ecological Applications, 12, 1247–1260.· Since its founding, conservation biology hasgreatly elaborated its research agenda; built stronger Barry, D. and Oelschlaeger, M. (1996). A science for surviv- al: values and conservation biology. Conservation Biology,connections with other fields and disciplines; ex- 10, 905–911. Batisse, M. (1986). Developing and focusing the Biospheretended its reach especially into aquatic and marine Reserve concept. Nature and Resources, 22, 2–11.environments; developed its professional capacity Beeman, R. S. and Pritchard, J. A. (2001). A green andfor training, research, and field application; become permanent land: ecology and agriculture in the twentiethan increasingly international field; and become in- century. University Press of Kansas, Lawrence, Kansas.creasingly active at the interface of conservation sci- Blandin, P. (2004). Biodiversity, between science and ethics.ence and policy. In S. H. Shakir, and W. Z. A. Mikhail, eds Soil zoology for sustainable development in the 21st Century, pp. 17–49. Eigenverlag, Cairo, Egypt.Suggested reading Boersma, P. D. (1996). Maine conservation: protecting the· Farnham, T. J. (2007). Saving Nature’s Legacy: Origins of the Idea of Biological Diversity. Yale University Press, exploited commons. Society for Conservation Biology Newsletter, 3, 1–6. Boersma, P. D., Kareiva, P., Fagan, W. F., Clark, J. A., and New Haven.· Hoekstra, J. M. (2001). How good are endangered Quammen, D. (1996). The Song of the Dodo: Island Bioge- species recovery plans? BioScience, 51, 643–650. ography in an Age of Extinctions. Simon and Schuster, Bohnsack, J. and Ault, J. (1996). Management strategies to New York. conserve marine biodiversity. Oceanography, 9, 73–81.· Meine, C. (2004). Correction Lines: Essays on Land, Leopold, and Conservation. Island Press, Washington, DC. Brussard, P. (1985). The current status of conservation biolo- gy. Bulletin of the Ecological Society of America, 66, 9–11.· Minteer, B. A. and Manning, R. E. (2003). Reconstructing Conservation: Finding Common Ground. Island Press, Callicott, J. B. (1990). Whither conservation ethics? Conser- vation Biology, 4, 15–20. Washington, DC. Caughley, G. and Gunn, A. (1986). Conservation biology in theory and practice. Blackwell Science, Cambridge, Massachusetts. CNT (Center For Neighborhood Technologies) and Open-Relevant website lands Project (2004). Natural connections: green infrastruc-· Society for Conservation Biology: http://www.conbio. org/ ture in Wisconsin, Illinois, and Indiana. (Online) Available at (Accessed February 2006). CEQ (Council On Environmental Quality) (1980). Environ- mental quality—1980: the eleventh annual report of the CEQ.REFERENCES US Government Printing Office, Washington, DC. Croker, R. A. (1991). Pioneer ecologist: the life and work ofAdams, J. S. (2005). The future of the wild: radical conservation Victor Ernest Shelford. Smithsonian Institution Press, for a crowded world. Beacon Press, Boston, Massachusetts. Washington, DC.Aguirre, A. A., Ostfeld, R. S., Tabor, G. M., House, C., and Crosby, A. W. (1986). Ecological imperialism: the biological Pearl, M. C. (2002). Conservation medicine: ecological health expansion of Europe, 900–1900. Cambridge University in practice. Oxford University Press, New York. Press, New York.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 38. 1 CONSERVATION BIOLOGY: PAST AND PRESENT 23Daly, H. E. and Cobb, J. B. Jr. (1989). For the common good: Golley, F. B. (1993). A history of the ecosystem concept in redirecting the economy toward community, the environment, ecology: more than the sum of the parts. Yale University and a sustainable future. Beacon Press, Boston, Press, New Haven, Connecticut. Massachusetts. Gómez-Pompa, A., Vázquez-Yanes, C., and Guevara, S.Dasmann, R. (1959). Environmental conservation. John Wiley (1972). The tropical rainforest: a non-renewable resource. and Sons, New York. Science, 177, 762–765.Dasmann, R. (1968). A different kind of country. Macmillan, Grifo, F. T. and Rosenthal, J., eds (1997). Biodiversity and New York. human health. Island Press, Washington, DC.Devall, B. and Sessions, G. (1985). Deep ecology: living as if Grove, R. H. (1995). Green imperialism: colonial expansion, nature mattered. Peregrine Smith Books, Salt Lake City, tropical island Edens, and the origins of environmentalism, Utah. 1600–1860. Cambridge University Press, Cambridge, UK.Diamond, J. M. (1997). Guns, germs, and steel: the fates of Grumbine, R. E. (1992). Ghost bears: exploring the biodiversity human societies. Norton, New York. crisis. Island Press, Washington, DC.Dunlap, T. R. (1988). Saving America’s wildlife: ecology and Grumbine, R. E. (1994a). Environmental policy and biodiver- the American mind, 1850–1990. Princeton University sity. Island Press, Washington, DC. Press, Princeton, New Jersey. Grumbine, R. E. (1994b). What is ecosystem management?Ehrenfeld, D. W. (1970). Biological conservation. Holt, Rine- Conservation Biology, 8, 27–38. hard, and Winston, New York. Grumbine, R. E. (1996). Using biodiversity as a justificationEhrenfeld, D. W. (1981). The arrogance of humanism. Oxford for nature protection in the U. S. Wild Earth, 6, 71–80. University Press, New York. Harris, L. D. (1984). 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  • 39. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLJacobson, S. K., Vaughan, E., and Miller, S. (1995). New Mayr, E. (1982). The growth of biological thought: diversity, directions in conservation biology: graduate programs. evolution, and inheritance. Harvard University Press, Conservation Biology, 9, 5–17. Cambridge, Massachusetts.Janzen, D. H. (1972). The uncertain future of the tropics. McCann, K. S. (2000). The diversity-stability debate. Natural History, 81, 80–90. Nature, 405, 228–233.Jensen, M. N. and Krausman, P. R. (1993). Conservation McIntosh, R. P. (1980). The background and some current biology’s literature: new wine or just a new bottle? problems of theoretical ecology. Synthese, 43, 195–255. Wildlife Society Bulletin, 21, 199–203. McIntosh, R. P. (1985). The background of ecology: concept andKnight, R. L. and Bates, S. F., eds (1995). A new century for theory. Cambridge University Press, Cambridge, UK. natural resources management. 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Conservation whereLidicker, W. Z., Jr. (1998). Revisiting the human dimen- people live and work. Conservation Biology, 16, 330–337. sion in conservation biology. Conservation Biology, 12, Myers, N. (1979). The sinking ark: a new look at the problem of 1170–1171. disappearing species. Pergamon Press, Oxford, England.Lovejoy, T. E. and Peters, R. L. (1994). Global warming and Myers, N. (1980). Conversion of tropical moist forests. National biological diversity. Yale University Press, New Haven, Academy of Sciences, Washington, DC. Connecticut. Myers, R. A., Hutchings, J. A., and Barrowman, N. J. (1997).Lubchenco, J., Olson, A. M., Brubaker, L. B., et al. (1991). Why do fish stocks collapse? The example of cod in The sustainable biosphere initiative: an ecological re- Atlantic Canada. Ecological Applications, 7, 91–106. search agenda. Ecology, 72, 371–412. Nash, R. (1989). The rights of nature: a history of environmentalMacArthur, R. (1972). Geographical ecology: patterns in the ethics. 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  • 40. 1 CONSERVATION BIOLOGY: PAST AND PRESENT 25Noss, R. F. (1990). Indicators for monitoring biodiversity: a Ripple, W. J. and Beschta, R. L. (2005). Linking wolves and hierarchical approach. Conservation Biology, 4, 355–364. plants: Aldo Leopold on trophic cascades. BioScience, 55,Noss, R. F. (1997). The failure of universities to produce 613–621. conservation biologists. Conservation Biology, 11, Roberts, C. M., Halpern, B., Palumbi, S. R., and Warner, R. 1267–1269. R. (2001). Designing marine reserve networks: whyNoss, R. F. (1999). Is there a special conservation biology? small, isolated protected areas are not enough. Conserva- Ecography, 22, 113–122. tion Biology in Practice, 2, 10–17.Noss, R. F. (2000). Science on the bridge. Conservation Biol- Rodríguez, J. P., Simonetti, J. A., Premoli, A., and Marini, ogy, 14, 333–335. M. Â. (2005). Conservation in Austral and NeotropicalNoss, R. F. and Cooperrider, A. Y. (1994). 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GAP analysis: Page, and Company, New York. a geographic approach to protection of biological diver-Pokras, M., Tabor, G., Pearl, M., Sherman, D., and Epstein, sity. Wildlife Monographs, 123, 1–41. P. (1997). Conservation medicine: an emerging field. In Sellars, R. W. (1997). Preserving nature in the national P. H. Raven, ed. Nature and human society: the quest for a parks: a history. Yale University Press, New Haven, Con- sustainable world, pp. 551–556. National Academy Press, necticut. Washington, DC. Shafer, C. L. (2001). Conservation biology trailblazers:Postel, S. and Richter, B. (2003). Rivers for life: managing George Wright, Ben Thompson, and Joseph Dixon. Con- water for people and nature. Island Press, Washington, DC. servation Biology, 15, 332–344.Primack, R. (1993). Essentials of conservation biology. Sinauer Sodhi, N. S., Brook, B. W., and Bradshaw, C. J. A. Associates, Sunderland, Massachusetts. (2007). Tropical conservation biology. Blackwell, Oxford,Pringle, R. M. (2008). Elephants as agents of habitat creation UK. for small vertebrates at patch scale. Ecology, 89, 26–33. Soulé, M. E. (1980). Thresholds for survival: criteria forPringle, R. M., Young, T. P., Rubenstein, D. I., and Mccauly, maintenance of fitness and evolutionary potential. In D. J. (2007). Herbivore-initiated interaction cascades and M. E. Soulé, and B. A. Wilcox, eds Conservation biology: their modulation by primary productivity in an African an evolutionary-ecological perspective, pp. 151–170. Sinauer savanna. Proceedings of the National Academy of Sciences of Associates, Sunderland, Massachusetts. the United States of America, 104, 193–197. Soulé, M. E. (1985). What is conservation biology? BioSci-Quammen, D. (1996). The song of the dodo: island biogeogra- ence, 35, 727–734. phy in an age of extinctions. Simon and Schuster, New Soulé, M. E., ed. (1986). Conservation biology: the science of York. scarcity and diversity. Sinauer Associates, Sunderland,Redford, K. 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  • 41. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLSoulé, M. E. (1987b). History of the Society for Conserva- Thorne-Miller, B. (1998). The Living Ocean: Understanding tion Biology: how and why we got here. Conservation and Protecting Marine Biodiversity, 2nd ed. Island Press, Biology, 1, 4–5. Washington, DC.Soulé, M. E. (1991). Land use planning and wildlife main- Trombulak, S. C. (1994). Undergraduate education and the tenance: guidelines for preserving wildlife in an urban next generation of conservation biologists. Conservation landscape. Journal of the American Planning Association, Biology, 8, 589–591. 57, 313–323. Udall, J. R. (1991). Launching the natural ark. Sierra, 7, 80–89.Soulé, M. E. and Terborgh, J., eds (1999). Continental conser- Wallace, A. R. (1863). On the physical geography of the vation: scientific foundations of regional reserve networks. Malay Archipelago. Journal of the Royal Geographical Washington, DC., Island Press. Society of London, 33, 217–234.Soulé, M. E. and Wilcox, B. A., eds (1980). Conservation Wang, Y. and Moskovits, D. K. (2001). Tracking fragmen- biology: an evolutionary-ecological perspective. Sinauer, tation of natural communities and changes in land cover: Sunderland, Massachusetts. applications of Landsat data for conservation in anTabor, G. M., Ostfeld, R. S., Poss, M., Dobson, A. P., and urban landscape (Chicago Wilderness). Conservation Aguirre, A. A. (2001). Conservation biology and the Biology, 15, 835–843. health sciences. In M. E. Soulé and G. H. Orians, eds Wilson, E. O. and Peter, F. M., eds (1988). Biodiversity. Conservation biology: research priorities for the next decade, National Academy Press, Washington, DC. pp. 155–173. Island Press, Washington, DC. WCED (World Commission On Environment and Devel-Takacs, D. (1996). The idea of biodiversity: philosophies of opment) (1987). Our common future. Oxford University paradise. Johns Hopkins University Press, Baltimore, Press, Oxford, UK. Maryland. Worster, D. (1979). Dust bowl: the southern plains in theTeer, J. G. (1988). Review of Conservation biology: the 1930s. Oxford University Press, New York. science of scarcity and diversity. Journal of Wildlife Man- Worster, D. (1985). Nature’s economy: a history of ecological agement, 52, 570–572. ideas. Cambridge University Press, Cambridge, UK.Terborgh, J. (1974). Preservation of natural diversity: Yaffee, S. L. (1994). The wisdom of the spotted owl: policy the problem of extinction prone species. BioScience, 24, lessons for a new century. Island Press, Washington, 715–722. DC.Thomas, W. L. Jr., Sauer, C. O., Bates, M., and Mumford, L. Ziswiler, V. (1967). Extinct and vanishing animals: a biolo- (1956). Man’s role in changing the face of the Earth. Univer- gy of extinction and survival. Springer-Verlag, New sity of Chicago Press, Chicago, Illinois. York.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 42. 1 CHAPTER 2 Biodiversity Kevin J. GastonBiological diversity or biodiversity (the latter term The scale of the variety of life is difficult, andis simply a contraction of the former) is the variety of perhaps impossible, for any of us truly to visua-life, in all of its many manifestations. It is a broad lize or comprehend. In this chapter I first attemptunifying concept, encompassing all forms, levels to give some sense of the magnitude of biodiver-and combinations of natural variation, at all levels sity by distinguishing between different key ele-of biological organization (Gaston and Spicer ments and what is known about their variation.2004). A rather longer and more formal definition Second, I consider how the variety of life hasis given in the international Convention on changed through time, and third and finallyBiological Diversity (CBD; the definition is how it varies in space. In short, the chapter will,provided in Article 2), which states that inevitably in highly summarized form, address“‘Biological diversity’ means the variability the three key issues of how much biodiversityamong living organisms from all sources includ- there is, how it arose, and where it can be, inter alia, terrestrial, marine and other aquaticecosystems and the ecological complexes of whichthey are part; this includes diversity within species, 2.1 How much biodiversity is there?between species and of ecosystems”. Whichever Some understanding of what the variety of lifedefinition is preferred, one can, for example, comprises can be obtained by distinguishing be-speak equally of the biodiversity of some given tween different key elements. These are the basicarea or volume (be it large or small) of the land or building blocks of biodiversity. For convenience,sea, of the biodiversity of a continent or an ocean they can be divided into three groups: geneticbasin, or of the biodiversity of the entire Earth. diversity, organismal diversity, and ecologicalLikewise, one can speak of biodiversity at present, diversity (Table 2.1). Within each, the elementsat a given time or period in the past or in the future, are organized in nested hierarchies, with thoseor over the entire history of life on Earth. higher order elements comprising lower order Table 2.1 Elements of biodiversity (focusing on those levels that are most commonly used). Modified from Heywood and Baste (1995). Ecological diversity Organismal diversity Biogeographic realms Domains or Kingdoms Biomes Phyla Provinces Families Ecoregions Genera Ecosystems Species Habitats Genetic diversity Subspecies Populations Populations Populations Individuals Individuals Chromosomes Genes Nucleotides 27© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 43. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLones. The three groups are intimately linked and eggs (diploid) develop into females and unfertil-share some elements in common. ized eggs (haploid) become males, hence the lat- ter have the minimal achievable single chromosome in their cells (Gould 1991). Humans2.1.1 Genetic diversity have 46 chromosomes (22 pairs of autosomes,Genetic diversity encompasses the components of and one pair of sex chromosomes).the genetic coding that structures organisms (nu- Within a species, genetic diversity is commonlycleotides, genes, chromosomes) and variation in measured in terms of allelic diversity (averagethe genetic make-up between individuals within a number of alleles per locus), gene diversity (het-population and between populations. This is the erozygosity across loci), or nucleotide differences.raw material on which evolutionary processes act. Large populations tend to have more genetic di-Perhaps the most basic measure of genetic diversity versity than small ones, more stable populationsis genome size—the amount of DNA (Deoxyribo- more than those that wildly fluctuate, and popu-nucleic acid) in one copy of a species’ chromosomes lations at the center of a species’ geographic range(also called the C-value). This can vary enormous- often have more genetic diversity than those atly, with published eukaryote genome sizes ranging the periphery. Such variation can have a varietybetween 0.0023 pg (picograms) in the parasitic mi- of population-level influences, including on pro-crosporidium Encephalitozoon intestinalis and 1400 ductivity/biomass, fitness components, behav-pg in the free-living amoeba Chaos chaos (Gregory ior, and responses to disturbance, as well as2008). These translate into estimates of 2.2 million influences on species diversity and ecosystemand 1369 billion base pairs (the nucleotides on op- processes (Hughes et al. 2008).posing DNA strands), respectively. Thus, even atthis level the scale of biodiversity is daunting. Cell 2.1.2 Organismal diversitysize tends to increase with genome size. Humanshave a genome size of 3.5 pg (3.4 billion base pairs). Organismal diversity encompasses the full taxo- Much of genome size comprises non-coding nomic hierarchy and its components, from indi-DNA, and there is usually no correlation between viduals upwards to populations, subspecies andgenome size and the number of genes coded. The species, genera, families, phyla, and beyond togenomes of more than 180 species have been kingdoms and domains. Measures of organismalcompletely sequenced and it is estimated that, for diversity thus include some of the most familiarexample, there are around 1750 genes for the bacte- expressions of biodiversity, such as the numbersria Haemophilus influenzae and 3200 for Escherichia of species (i.e. species richness). Others should becoli, 6000 for the yeast Saccharomyces cerevisiae, 19 000 better studied and more routinely employed thanfor the nematode Caenorhabditis elegans, 13 500 for they have been thus far.the fruit fly Drosophila melanogaster, and $25 000 for Starting at the lowest level of organismal diver-the plant Arabidopsis thaliana, the mouse Mus muscu- sity, little is known about how many individuallus, brown rat Rattus norvegicus and human Homo organisms there are at any one time, although thissapiens. There is strong conservatism of some genes is arguably an important measure of the quantityacross much of the diversity of life. The differences in and variety of life (given that, even if sometimesgenetic composition of species give us indications of only in small ways, most individuals differ fromtheir relatedness, and thus important information as one another). Nonetheless, the numbers must beto how the history and variety of life developed. extraordinary. The global number of prokaryotes Genes are packaged into chromosomes. The has been estimated to be 4–6 x 1030 cells—manynumber of chromosomes per somatic cell thus million times more than there are stars in thefar observed varies between 2 for the jumper ant visible universe (Copley 2002)—with a produc-Myrmecia pilosula and 1260 for the adders-tongue tion rate of 1.7 x 1030 cells per annum (Whitman etfern Ophioglossum reticulatum. The ant species re- al. 1998). The numbers of protists is estimated atproduces by haplodiploidy, in which fertilized 104À107 individuals per m2 (Finlay 2004).© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 44. 1 BIODIVERSITY 29Impoverished habitats have been estimated to plying standard species concepts, in culturing thehave 105 individual nematodes per m2, and vast majority of these organisms and thereby ap-more productive habitats 106À107 per m2, possi- plying classical identification techniques, and bybly with an upper limit of 108 per m2; 1019 has the vast numbers of individuals. Indeed, depend-been suggested as a conservative estimate of the ing on the approach taken, the numbers of pro-global number of individuals of free-living nema- karyotic species estimated to occur even in verytodes (Lambshead 2004). By contrast, it has small areas can vary by a few orders of magni-been estimated that globally there may be less than tude (Curtis et al. 2002; Ward 2002). The rate of1011 breeding birds at any one time, fewer than 17 reassociation of denatured (i.e. single stranded)for every person on the planet (Gaston et al. 2003). DNA has revealed that in pristine soils and sedi- Individual organisms can be grouped into rela- ments with high organic content samples of 30 totively independent populations of a species on the 100 cm3 correspond to c. 3000 to 11 000 differentbasis of limited gene flow and some level of genet- genomes, and may contain 104 different prokary-ic differentiation (as well as on ecological criteria). otic species of equivalent abundances (TorsvikThe population is a particularly important ele- et al. 2002). Samples from the intestinal microbialment of biodiversity. First, it provides an impor- flora of just three adult humans contained repre-tant link between the different groups of elements sentatives of 395 bacterial operational taxonomicof biodiversity (Table 2.1). Second, it is the scale at units (groups without formal designation of tax-which it is perhaps most sensible to consider lin- onomic rank, but thought here to be roughlykages between biodiversity and the provision of equivalent to species), of which 244 were previ-ecosystem services (supporting services—e.g. nu- ously unknown, and 80% were from species thattrient cycling, soil formation, primary production; have not been cultured (Eckburg et al. 2005). Like-provisioning services—e.g. food, freshwater, wise, samples from leaves were estimated to har-timber and fiber, fuel; regulating services—e.g. bor at least 95 to 671 bacterial species from each ofclimate regulation, flood regulation, disease regu- nine tropical tree species, with only 0.5% com-lation, water purification; cultural services—e.g. mon to all the tree species, and almost all of theaesthetic, spiritual, educational, recreational; bacterial species being undescribed (LambaisMEA 2005). Estimates of the density of such po- et al. 2006). On the basis of such findings, globalpulations and the average geographic range sizes prokaryote diversity has been argued to compriseof species suggest a total of about 220 distinct possibly millions of species, and some have sug-populations per eukaryote species (Hughes et al. gested it may be many orders of magnitude more1997). Multiplying this by a range of estimates of than that (Fuhrman and Campbell 1998; Dykhui-the extant numbers of species, gives a global total zen 1998; Torsvik et al. 2002; Venter et al. 2004).of 1.1 to 6.6 x 109 populations (Hughes et al. 1997), Although much more certainty surrounds es-one or fewer for every person on the planet. The timates of the numbers of eukaryotic than pro-accuracy of this figure is essentially unknown, karyotic species, this is true only in a relative andwith major uncertainties at each step of the calcu- not an absolute sense. Numbers of eukaryoticlation, but the ease with which populations can be species are still poorly understood. A wide vari-eradicated (e.g. through habitat destruction) sug- ety of approaches have been employed to esti-gests that the total is being eroded at a rapid rate. mate the global numbers in large taxonomic People have long pondered one of the impor- groups and, by summation of these estimates,tant contributors to the calculation of the total how many extant species there are overall.number of populations, namely how many differ- These approaches include extrapolations basedent species of organisms there might be. Greatest on counting species, canvassing taxonomic ex-uncertainty continues to surround the richness of perts, temporal patterns of species description,prokaryotes, and in consequence they are often proportions of undescribed species in samples,ignored in global totals of species numbers. This well-studied areas, well-studied groups, species-is in part variously because of difficulties in ap- abundance distributions, species-body size© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 45. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLdistributions, and trophic relations (Gaston single unified, complete and maintained database2008). One recent summary for eukaryotes of valid formal names. However, probably aboutgives lower and upper estimates of 3.5 and 108 2 million extant species are regarded as beingmillion species, respectively, and a working fig- known to science (MEA 2005). Importantly, thisure of around 8 million species (Table 2.2). Based total hides two kinds of error. First, there areon current information the two extremes seem instances in which the same species is knownrather unlikely, but the working figure at least under more than one name (synonymy). This isseems tenable. However, major uncertainties more frequent amongst widespread species,surround global numbers of eukaryotic species which may show marked geographic variationin particular environments which have been in morphology, and may be described anew re-poorly sampled (e.g. deep sea, soils, tropical peatedly in different regions. Second, one nameforest canopies), in higher taxa which are ex- may actually encompass multiple species (hom-tremely species rich or with species which are onymy). This typically occurs because these spe-very difficult to discriminate (e.g. nematodes, cies are very closely related, and look very similararthropods), and in particular functional groups (cryptic species), and molecular analyses may bewhich are less readily studied (e.g. parasites). A required to recognize or confirm their differences.wide array of techniques is now being employed Levels of as yet unresolved synonymy are un-to gain access to some of the environments that doubtedly high in many taxonomic groups. In-have been less well explored, including rope deed, the actual levels have proven to be a keyclimbing techniques, aerial walkways, cranes issue in, for example, attempts to estimate theand balloons for tropical forest canopies, and global species richness of plants, with the highlyremotely operated vehicles, bottom landers, sub- variable synonymy rate amongst the few groupsmarines, sonar, and video for the deep ocean. that have been well studied in this regard makingMolecular and better imaging techniques are difficult the assessment of the overall level ofalso improving species discrimination. Perhaps synonymy across all the known species. Equally,most significantly, however, it seems highly however, it is apparent that cryptic speciesprobable that the majority of species are para- abound, with, for example, one species of neo-sites, and yet few people tend to think about tropical skipper butterfly recently having beenbiodiversity from this viewpoint. shown actually to be a complex of ten species How many of the total numbers of species have (Hebert et al. 2004).been taxonomically described remains surpris- New species are being described at a rateingly uncertain, in the continued absence of a of about 13 000 per annum (Hawksworth and Table 2.2 Estimates (in thousands), by different taxonomic groups, of the overall global numbers of extant eukaryote species. Modified from Hawksworth and Kalin‐Arroyo (1995) and May (2000). Overall species High Low Working figure Accuracy of working figure ‘Protozoa’ 200 60 100 very poor ‘Algae’ 1000 150 300 very poor Plants 500 300 320 good Fungi 2700 200 1500 moderate Nematodes 1000 100 500 very poor Arthropods 101 200 2375 4650 moderate Molluscs 200 100 120 moderate Chordates 55 50 50 good Others 800 200 250 moderate Totals 107 655 3535 7790 very poor© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 46. 1 BIODIVERSITY 31Kalin-Arroyo 1995), or about 36 species on the tems, ecoregions, provinces, and on up to biomesaverage day. Given even the lower estimates of and biogeographic realms (Table 2.1). This is anoverall species numbers this means that there is important dimension to biodiversity not readilylittle immediate prospect of greatly reducing the captured by genetic or organismal diversity, andnumbers that remain unknown to science. This is in many ways is that which is most immediatelyparticularly problematic because the described apparent to us, giving the structure of the naturalspecies are a highly biased sample of the extant and semi-natural world in which we live. How-biota rather than the random one that might en- ever, ecological diversity is arguably also the leastable more ready extrapolation of its properties to satisfactory of the groups of elements of biodiver-all extant species. On average, described species sity. There are two reasons. First, whilst thesetend to be larger bodied, more abundant and elements clearly constitute useful ways of break-more widespread, and disproportionately from ing up continua of phenomena, they are difficulttemperate regions. Nonetheless, new species con- to distinguish without recourse to what ultimate-tinue to be discovered in even otherwise relative- ly constitute some essentially arbitrary rules. Forly well-known taxonomic groups. New extant example, whilst it is helpful to be able to labelfish species are described at the rate of about different habitat types, it is not always obvious130–160 each year (Berra 1997), amphibian spe- precisely where one should end and anothercies at about 95 each year (from data in Frost begin, because no such beginnings and endings2004), bird species at about 6–7 each year (Van really exist. In consequence, numerous schemesRootselaar 1999, 2002), and terrestrial mammals have been developed for distinguishing betweenat 25–30 each year (Ceballos and Ehrlich 2009). many elements of ecological diversity, often withRecently discovered mammals include marsu- wide variation in the numbers of entities recog-pials, whales and dolphins, a sloth, an elephant, nized for a given element. Second, some of theprimates, rodents, bats and ungulates. elements of ecological diversity clearly have both Given the high proportion of species that have abiotic and biotic components (e.g. ecosystems,yet to be discovered, it seems highly likely that ecoregions, biomes), and yet biodiversity is de-there are entire major taxonomic groups of organ- fined as the variety of life.isms still to be found. That is, new examples of Much recent interest has focused particularlyhigher level elements of organismal diversity. on delineating ecoregions and biomes, principal-This is supported by recent discoveries of possi- ly for the purposes of spatial conservationble new phyla (e.g. Nanoarchaeota), new orders planning (see Chapter 11), and there has thus(e.g. Mantophasmatodea), new families (e.g. As- been a growing sense of standardization of thepidytidae) and new subfamilies (e.g. Martiali- schemes used. Ecoregions are large areal unitsnae). Discoveries at the highest taxonomic levels containing geographically distinct species as-have particularly served to highlight the much semblages and experiencing geographically dis-greater phyletic diversity of microorganisms tinct environmental conditions. Carefulcompared with macroorganisms. Under one clas- mapping schemes have identified 867 terrestrialsification 60% of living phyla consist entirely or ecoregions (Figure 2.1 and Plate 1; Olson et al.largely of unicellular species (Cavalier-Smith 2001), 426 freshwater ecoregions (Abell et al.2004). Again, this perspective on the variety of 2008), and 232 marine coastal shelf area ecor-life is not well reflected in much of the literature egions (Spalding et al. 2007). Ecoregions can inon biodiversity. turn be grouped into biomes, global-scale bio- geographic regions distinguished by unique col- lections of species assemblages and ecosystems.2.1.3 Ecological diversity Olson et al. (2001) distinguish 14 terrestrialThe third group of elements of biodiversity en- biomes, some of which at least will be very fa-compasses the scales of ecological differences miliar wherever in the world one resides (tropi-from populations, through habitats, to ecosys- cal subtropical moist broadleaf forests;© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 47. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLFigure 2.1 The terrestrial ecoregions. Reprinted from Olson et al. (2001).tropical subtropical dry broadleaf forests; Westerlies, Trades and Coastal boundary), whichtropical subtropical coniferous forests; tem- are then subdivided, on the basis principallyperate broadleaf mixed forests; temperate co- of biogeochemical features, into a further 12niferous forests; boreal forest/taiga; tropical biomes (Antarctic Polar, Antarctic Westerlysubtropical grasslands, savannas shrublands; Winds, Atlantic Coastal, Atlantic Polar, Atlantictemperate grasslands, savannas shrublands; Trade Wind, Atlantic Westerly Winds, Indianflooded grasslands savannas; montane grass- Ocean Coastal, Indian Ocean Trade Wind, Pacificlands shrublands; tundra; Mediterranean for- Coastal, Pacific Polar, Pacific Trade Wind, Pacificests, woodlands scrub; deserts xeric Westerly Winds), and then into a finer 51 unitsshrublands; mangroves). (Longhurst 1998). At a yet coarser spatial resolution, terrestrialand aquatic systems can be divided into bio- 2.1.4 Measuring biodiversitygeographic realms. Terrestrially, eight suchrealms are typically recognized, Australasia, Given the multiple dimensions and the complex-Antarctic, Afrotropic, Indo-Malaya, Nearctic, ity of the variety of life, it should be obvious thatNeotropic, Oceania and Palearctic (Olson et al. there can be no single measure of biodiversity2001). Marine coastal shelf areas have been (see Chapter 16). Analyses and discussions ofdivided into 12 realms (Arctic, Temperate biodiversity have almost invariably to be framedNorth Atlantic, Temperate Northern Pacific, in terms of particular elements or groups of ele-Tropical Atlantic, Western Indo-Pacific, Central ments, although this may not always be apparentIndo-Pacific, Eastern Indo-Pacific, Tropical from the terminology being employed (the termEastern Pacific, Temperate South America, ‘biodiversity’ is used widely and without explicitTemperate Southern Africa, Temperate Austra- qualification to refer to only some subset of thelasia, and Southern Ocean; Spalding et al. variety of life). Moreover, they have to be framed2007). There is no strictly equivalent scheme in terms either of “number” or of “heterogeneity”for the pelagic open ocean, although one has measures of biodiversity, with the former disre-divided the oceans into four primary units (Polar, garding the degrees of difference between the© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 48. 1 BIODIVERSITY 33occurrences of an element of biodiversity and the 2.2 How has biodiversity changedlatter explicitly incorporating such differences. through time?For example, organismal diversity could be ex- The Earth is estimated to have formed, by thepressed in terms of species richness, which is a accretion through large and violent impacts ofnumber measure, or using an index of diversity numerous bodies, approximately 4.5 billionthat incorporates differences in the abundances of years ago (Ga). Traditionally, habitable worldsthe species, which is a heterogeneity measure. are considered to be those on which liquidThe two approaches constitute different re- water is stable at the surface. On Earth, both thesponses to the question of whether biodiversity atmosphere and the oceans may well have startedis similar or different in an assemblage in which a to form as the planet itself did so. Certainly, life issmall proportion of the species comprise most of thought to have originated on Earth quite early inthe individuals, and therefore would predomi- its history, probably after about 3.8–4.0 Ga, whennantly be obtained in a small sample of indivi- impacts from large bodies from space are likely toduals, or in an assemblage of the same total have declined or ceased. It may have originatednumber of species in which abundances are in a shallow marine pool, experiencing intensemore evenly distributed, and thus more species radiation, or possibly in the environment of awould occur in a small sample of individuals deeper water hydrothermal vent. Because of the(Purvis and Hector 2000). The distinction be- subsequent recrystallisation and deformation oftween number and heterogeneity measures is the oldest sediments on Earth, evidence for earlyalso captured in answers to questions that reflect life must be found in its metabolic interactiontaxonomic heterogeneity, for example whether the with the environment. The earliest, and highlyabove-mentioned group of 10 skipper butterflies controversial, evidence of life, from such indirectis as biodiverse as a group of five skipper species geochemical data, is from more than 3.83 billionand five swallowtail species (e.g. Hendrickson years ago (Dauphas et al. 2004). Relatively unam-and Ehrlich 1971). biguous fossil evidence of life dates to 2.7 Ga In practice, biodiversity tends most commonly (López-García et al. 2006). Either way, life hasto be expressed in terms of number measures of thus been present throughout much of the Earth’sorganismal diversity, often the numbers of a given existence. Although inevitably attention tends totaxonomic level, and particularly the numbers of fall on more immediate concerns, it is perhapsspecies. This is in large part a pragmatic choice. worth occasionally recalling this deep heritage inOrganismal diversity is better documented and the face of the conservation challenges of today.often more readily estimated than is genetic diver- For much of this time, however, life comprisedsity, and more finely and consistently resolved Precambrian chemosynthetic and photosyntheticthan much of ecological diversity. Organismal prokaryotes, with oxygen-producing cyanobac-diversity, however, is problematic inasmuch as teria being particularly important (Labandeirathe majority of it remains unknown (and thus 2005). Indeed, the evolution of oxygenic photo-studies have to be based on subsets), and precisely synthesis, followed by oxygen becoming a majorhow naturally and well many taxonomic groups component of the atmosphere, brought about aare themselves delimited remains in dispute. dramatic transformation of the environmentPerhaps most importantly it also remains but on Earth. Geochemical data has been argued toone, and arguably a quite narrow, perspective on suggest that oxygenic photosynthesis evolvedbiodiversity. before 3.7 Ga (Rosing and Frei 2004), although Whilst accepting the limitations of measuring others have proposed that it could not have arisenbiodiversity principally in terms of organismal before c.2.9 Ga (Kopp et al. 2005).diversity, the following sections on temporal These cyanobacteria were initially responsibleand spatial variation in biodiversity will follow for the accumulation of atmospheric oxygen. Thisthis course, focusing in many cases on species in turn enabled the emergence of aerobicallyrichness.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 49. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLmetabolizing eukaryotes. At an early stage, eu- to address its associated biases to determine thosekaryotes incorporated within their structure aer- actual patterns. The best fossil data are for marineobically metabolizing bacteria, giving rise to invertebrates and it was long thought that theseeukaryotic cells with mitochondria; all anaerobi- principally demonstrated a dramatic rise in diver-cally metabolizing eukaryotes that have been sity, albeit punctuated by significant periods ofstudied in detail have thus far been found to stasis and mass extinction events. However, ana-have had aerobic ancestors, making it highly lyses based on standardized sampling havelikely that the ancestral eukaryote was aerobic markedly altered this picture (Figure 2.2). They(Cavalier-Smith 2004). This was a fundamentally identify the key features of change in the numbersimportant event, leading to heterotrophic micro- of genera (widely assumed to correlate with spe-organisms and sexual means of reproduction. cies richness) as comprising: (i) a rise in richnessSuch endosymbiosis occurred serially, by simpler from the Cambrian through to the mid-Devonianand more complex routes, enabling eukaryotes to ($525–400 million years ago, Ma); (ii) a largediversify in a variety of ways. Thus, the inclusion extinction in the mid-Devonian with no clear re-of photosynthesizing cyanobacteria into a eu- covery until the Permian ($400–300 Ma); (iii) akaryote cell that already contained a mitochon- large extinction in the late-Permian and again indrion gave rise to eukaryotic cells with plastids the late-Triassic ($250–200 Ma); and (iv) a rise inand capable of photosynthesis. This event alone richness through the late-Triassic to the presentwould lead to dramatic alterations in the Earth’s ($200–0 Ma; Alroy et al. 2008).ecosystems. Whatever the detailed pattern of change in di- Precisely when eukaryotes originated, when versity through time, most of the species thatthey diversified, and how congruent was the have ever existed are extinct. Across a variety ofdiversification of different groups remains un- groups (both terrestrial and marine), the bestclear, with analyses giving a very wide range of present estimate based on fossil evidence is thatdates (Simpson and Roger 2004). The uncertainty, the average species has had a lifespan (from itswhich is particularly acute when attempting to appearance in the fossil record until the time itunderstand evolutionary events in deep time, re- disappeared) of perhaps around 1–10 Myrsults principally from the inadequacy of the fossil (McKinney 1997; May 2000). However, the varia-record (which, because of the low probabilities of bility both within and between groups is veryfossilization and fossil recovery, will always tend marked, making estimation of what is the overallto underestimate the ages of taxa) and the diffi- average difficult. The longest-lived species that isculties of correctly calibrating molecular clocks so well documented is a bryozoan that persistedas to use the information embodied in genetic from the early Cretaceous to the present, a periodsequences to date these events. Nonetheless, of approximately 85 million years (May 2000). Ifthere is increasing convergence on the idea that the fossil record spans 600 million years, totalmost known eukaryotes can be placed in one of species numbers were to have been roughly con-five or six major clades—Unikonts (Opisthokonts stant over this period, and the average life span ofand Amoebozoa), Plantae, Chromalveolates, Rhi- individual species were 1–10 million years, thenzaria and Excavata (Keeling et al. 2005; Roger and at any specific instant the extant species wouldHug 2006). have represented 0.2–2% of those that have ever Focusing on the last 600 million years, attention lived (May 2000). If this were true of the presentshifts somewhat from the timing of key diversifi- time then, if the number of extant eukaryote spe-cation events (which becomes less controversial) cies numbers 8 million, 400 million might onceto how diversity per se has changed through time have existed.(which becomes more measurable). Arguably the The frequency distribution of the numbers ofcritical issue is how well the known fossil record time periods with different levels of extinction isreflects the actual patterns of change that took markedly right-skewed, with most periods hav-place and how this record can best be analyzed ing relatively low levels of extinction and a© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 50. 1 BIODIVERSITY 35 800 600 Number of genera 400 200 0 Cm O S D C P Tr J K Pg Ng 500 400 300 200 100 0 Time (Ma)Figure 2.2 Changes in generic richness of marine invertebrates over the last 600 million years based on a sampling‐standardized analysis of the fossilrecord. Ma, million years ago. Reprinted from Alroy et al. (2008) with permission from AAAS (American Association for the Advancement of Science).minority having very high levels (Raup 1994). lion years (Erwin 1998), and the resultant assem-The latter are the periods of mass extinction blages have invariably had a markedly differentwhen 75–95% of species that were extant are es- composition from those that preceded a masstimated to have become extinct. Their signifi- extinction, with groups which were previouslycance lies not, however, in the overall numbers highly successful in terms of species richnessof extinctions for which they account (over the being lost entirely or persisting at reducedlast 500 Myr this has been rather small), but in the numbers.hugely disruptive effect they have had on thedevelopment of biodiversity. Clearly neither ter-restrial nor marine biotas are infinitely resilient toenvironmental stresses. Rather, when pushed be- 2.3 Where is biodiversity?yond their limits they can experience dramatic Just as biodiversity has varied markedly throughcollapses in genetic, organismal and ecological time, so it also varies across space. Indeed, onediversity (Erwin 2008). This is highly significant can think of it as forming a richly textured landgiven the intensity and range of pressures that and seascape, with peaks (hotspots) and troughshave been exerted on biodiversity by humankind, (coldspots), and extensive plains in between (Fig-and which have drastically reshaped the natural ure 2.3 and Plate 2, and 2.4 and Plate 3; Gastonworld over a sufficiently long period in respect to 2000). Even locally, and just for particular groups,available data that we have rather little concept of the numbers of species can be impressive, withwhat a truly natural system should look like for example c.900 species of fungal fruiting bodies(Jackson 2008). Recovery from past mass extinc- recorded from 13 plots totaling just 14.7 ha (hect-tion events has invariably taken place. But, whilst are) near Vienna, Austria (Straatsma and Krisai-this may have been rapid in geological terms, it Greilhuber 2003), 173 species of lichens on ahas nonetheless taken of the order of a few mil- single tree in Papua New Guinea (Aptroot© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 51. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLFigure 2.3 Global richness patterns for birds of (a) species, (b) genera, (c) families, and (d) orders. Reprinted from Thomas et al. (2008).1997), 814 species of trees from a 50 ha study plot sive inventory of all of the species that are presentin Peninsular Malaysia (Manokaran et al. 1992), (microorganisms typically remain insufficiently850 species of invertebrates estimated to occur at documented even in otherwise well studieda sandy beach site in the North Sea (Armonies areas), knowledge of the basic patterns has beenand Reise 2000), 245 resident species of birds developing rapidly. Although long constrainedrecorded holding territories on a 97 ha plot in to data on higher vertebrates, the breadth of or-Peru (Terborgh et al. 1990), and 200 species of ganisms for which information is available hasmammals occurring at some sites in the Amazo- been growing, with much recent work particular-nian rain forest (Voss and Emmons 1996). ly attempting to determine whether microorgan- Although it remains the case that for no even isms show the same geographic patterns as domoderately sized area do we have a comprehen- other groups.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 52. 1 BIODIVERSITY 37Figure 2.4 Global species richness patterns of birds, mammals, and amphibians, for total, rare (those in the lower quartile of range size for eachgroup) and threatened (according to the IUCN criteria) species. Reprinted from Grenyer et al. (2006).2.3.1 Land and water Gondwana from $180 Ma) is important in ex- plaining why there are more species in terrestrialThe oceans cover $340.1 million km (67%), the 2 systems than in marine ones. Finally, the extremeland $170.3 million km2 (33%), and freshwaters fragmentation and isolation of freshwater bodies(lakes and rivers) $1.5 million km2 (0.3%; with seems key to why these are so diverse for theiranother 16 million km2 under ice and permanent area.snow, and 2.6 million km2 as wetlands, soil waterand permafrost) of the Earth’s surface. It wouldtherefore seem reasonable to predict that the 2.3.2 Biogeographic realms and ecoregionsoceans would be most biodiverse, followed bythe land and then freshwaters. In terms of num- Of the terrestrial realms, the Neotropics is gener-bers of higher taxa, there is indeed some evidence ally regarded as overall being the most biodi-that marine systems are especially diverse. For verse, followed by the Afrotropics and Indo-example, of the 96 phyla recognized by Margulis Malaya, although the precise ranking of theseand Schwartz (1998), about 69 have marine repre- tropical regions depends on the way in whichsentatives, 55 have terrestrial ones, and 60 have organismal diversity is measured. For example,freshwater representatives. However, of the spe- for species the richest realm is the Neotropics forcies described to date only about 15% are marine amphibians, reptiles, birds and mammals, but forand 6% are freshwater. The fact that life began in families it is the Afrotropics for amphibians andthe sea seems likely to have played an important mammals, the Neotropics for reptiles, and therole in explaining why there are larger numbers Indo-Malayan for birds (MEA 2005). In parts,of higher taxa in marine systems than in terrestri- these differences reflect variation in the historiesal ones. The heterogeneity and fragmentation of of the realms (especially mountain uplift and cli-the land masses (particularly that associated mate changes) and the interaction with the emer-with the breakup of the “supercontinent” of gence and spread of the groups, albeit perhaps© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 53. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL Table 2.3 The five most species rich terrestrial ecoregions for each of four vertebrate groups. AT – Afrotropic, IM – Indo‐Malaya, NA – Nearctic, and NT–Neotropic. Data from Olson et al. (2001). Amphibians Reptiles Birds Mammals 1 Northwestern Andean Peten‐Veracruz Northern Indochina Sierra Madre de Oaxaca montane forests moist forests (NT) subtropical forests (IM) pine‐oak forests (NT) (NT) 2 Eastern Cordillera real Southwest Amazon Southwest Amazon moist Northern Indochina montane forests moist forests (NT) forests (NT) subtropical forests (NT) (IM) 3 Napo moist forests (NT) Napo moist forests Albertine Rift montane Sierra Madre Oriental (NT) forests (AT) pine‐oak forests (NA) 4 Southwest Amazon Southern Pacific dry Central Zambezian Miombo Southwest Amazon moist forests (NT) forests (NT) woodlands (AT) moist forests (NT) 5 Choco‐Darien moist Central American Northern Acacia‐ Central Zambezian forests (NT) pine‐oak forests Commiphora bushlands Miombo woodlands (NT) thickets (AT) (AT)complicated by issues of geographic consistency richness (and some other elements of organismalin the definition of higher taxonomic groupings. diversity) towards lower (tropical) latitudes. The Western Indo-Pacific and Central Several features of this gradient are of note:Indo-Pacific realms have been argued to be a (i) it is exhibited in marine, terrestrial and fresh-center for the evolutionary radiation of many waters, and by virtually all major taxonomicgroups, and are thought to be perhaps the global groups, including microbes, plants, invertebrateshotspot of marine species richness and endemism and vertebrates (Hillebrand 2004; Fuhrman et al.(Briggs 1999; Roberts et al. 2002). With a shelf area 2008); (ii) it is typically manifest whether biodi-of 6 570 000 km2, which is considered to be a versity is determined at local sites, across largesignificant influence, it has more than 6000 spe- regions, or across entire latitudinal bands; (iii) itcies of molluscs, 800 species of echinoderms, 500 has been a persistent feature of much of thespecies of hermatypic (reef forming) corals, and history of life on Earth (Crane and Lidgard4000 species of fish (Briggs 1999). 1989; Alroy et al. 2008); (iv) the peak of diversity At the scale of terrestrial ecoregions, the most is seldom at the equator itself, but seems often tospeciose for amphibians and reptiles are in the be displaced somewhat further north (often atNeotropics, for birds in Indo-Malaya, Neotropics $20–30 N); (v) it is commonly, though far fromand Afrotropics, and for mammals in the Neo- universally, asymmetrical about the equator, in-tropics, Indo-Malaya, Nearctic, and Afrotropics creasing rapidly from northern regions to the(Table 2.3). Amongst the freshwater ecoregions, equator and declining slowly from the equatorthose with globally high richness of freshwater to southern regions; and (vi) it varies markedlyfish include the Brahmaputra, Ganges, and in steepness for different major taxonomicYangtze basins in Asia, and large portions of groups with, for example, butterflies beingthe Mekong, Chao Phraya, and Sitang and Irra- more tropical than birds.waddy; the lower Guinea in Africa; and the Although it attracts much attention in its ownParaná and Orinoco in South America (Abell right, it is important to see the latitudinal patternet al. 2008). in species richness as a component of broader spatial patterns of richness. As such, the mechan- isms that give rise to it are also those that give rise2.3.3 Latitude to those broader patterns. Ultimately, higher spe-Perhaps the best known of all spatial patterns in cies richness has to be generated by some combi-biodiversity is the general increase in species nation of greater levels of speciation (a cradle of© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 54. 1 BIODIVERSITY 39diversity), lower levels of extinction (a museum progressively to decrease with distance from seaof diversity) or greater net movements of geo- level (above or below) and to show a pronouncedgraphic ranges. It is likely that their relative im- hump-shaped pattern in which it first increasesportance in giving rise to latitudinal gradients and then declines (Angel 1994; Rahbek 1995;varies with taxon and region. This said, greater Bryant et al. 2008). The latter pattern tendslevels of speciation at low latitudes and range to become more apparent when the effects ofexpansion of lineages from lower to higher variation in area have been accounted for, and islatitudes seem to be particularly important probably the more general, although in either(Jablonski et al. 2006; Martin et al. 2007). More case richness tends to be lowest at the mostproximally, key constraints on speciation and ex- extreme elevations or depths.tinction rates and range movements are thought Microbial assemblages can be found at consid-to be levels of: (i) productive energy, which influ- erable depths (in some instances up to a few kilo-ence the numbers of individuals that can be sup- meters) below the terrestrial land surface and theported, thereby limiting the numbers of species seafloor, often exhibiting unusual metabolic cap-that can be maintained in viable populations; abilities (White et al. 1998; D’Hondt et al. 2004).(ii) ambient energy, which influences mutation Knowledge of these assemblages remains, how-rates and thus speciation rates; (iii) climatic vari- ever, extremely poor, given the physical chal-ation, which on ecological time scales influences lenges of sampling and of doing so withoutthe breadth of physiological tolerances and contamination from other sources.dispersal abilities and thus the potential for pop-ulation divergence and speciation, and on evolu-tionary time scales influences extinctions (e.g.through glacial cycles) and recolonizations; and 2.4 In conclusion(iv) topographic variation, which enhances the Understanding of the nature and scale of biodi-likelihood of population isolation and thus speci- versity, of how it has changed through time, andation (Gaston 2000; Evans et al. 2005; Clarke and of how it varies spatially has developed immea-Gaston 2006; Davies et al. 2007). surably in recent decades. Improvements in the levels of interest, the resources invested and the application of technology have all helped. In-2.3.4 Altitude and Depth deed, it seems likely that the basic principlesVariations in depth in marine systems and alti- are in the main well established. However,tude in terrestrial ones are small relative to the much remains to be learnt. The obstacles areareal coverage of these systems. The oceans aver- fourfold. First, the sheer magnitude and com-age c.3.8 km in depth but reach down to 10.9 km plexity of biodiversity constitute a huge chal-(Challenger Deep), and land averages 0.84 km in lenge to addressing perhaps the majority ofelevation and reaches up to 8.85 km (Mt. Everest). questions that are posed about it, and one thatNonetheless, there are profound changes in or- is unlikely to be resolved in the near future.ganismal diversity both with depth and altitude. Second, the biases of the fossil record and theThis is in large part because of the environmental apparent variability in rates of molecular evolu-differences (but also the effects of area and isola- tion continue to thwart a better understanding oftion), with some of those changes in depth or the history of biodiversity. Third, knowledge ofaltitude of a few hundred meters being similar the spatial patterning of biodiversity is limitedto those experienced over latitudinal distances of by the relative paucity of quantitative samplingseveral hundred kilometers (e.g. temperature). of biodiversity over much of the planet. Finally, In both terrestrial and marine (pelagic and ben- the levels and patterns of biodiversity arethic) systems, species richness across a wide vari- being profoundly altered by human activitiesety of taxonomic groups has been found (see Box 2.1 and Chapter 10).© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 55. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL Box 2.1 Invaluable biodiversity inventories Navjot S. Sodhi This chapter defines biodiversity. Due to (34–43%) in butterflies, freshwater fish, birds, massive loss of native habitats around the and mammals. Due to low endemism in globe (Chapter 4), biodiversity is rapidly being Singapore, all of these extinctions likely eroded (Chapter 10). Therefore, it is critical to represented population than species understand which species will survive human extinctions (see Box 10.1). Using extinction data onslaught and which will not. We also need to from Singapore, Brook et al. (2003) also comprehend the composition of new projected that if the current levels of communities that arise after the loss or deforestation in Southeast Asia continue, disturbance of native habitats. Such a between 13–42% of regional populations could determination needs a “peek” into the past. be lost by 2100. Half of these extinctions could That is, which species were present before the represent global species losses. habitat was disturbed. Perhaps naturalists in Fragments are becoming a prevalent feature the 19th and early 20th centuries did not in most landscapes around the globe (Chapter 5). realize that they were doing a great service to Very little is known about whether fragments future conservation biologists by publishing can sustain forest biodiversity over the long‐ species inventories. These historic inventories term. Using an old species inventory, Sodhi et al. are treasure troves—they can be used as (2005) studied the avifaunal change over 100 baselines for current (and future) species loss years (1898–1998) in a four hectare patch of rain and turnover assessments. forest in Singapore (Singapore Botanic Gardens). Singapore represents a worst‐case scenario in Over this period, many forest species (e.g. green tropical deforestation. This island (540 km2) has broadbill (Calyptomena viridis); Box 2.1 Figure) lost over 95% of its primary forests since 1819. were lost, and replaced with introduced species Comparing historic and modern inventories, such as the house crow (Corvus splendens). By Brook et al. (2003) could determine losses in 1998, 20% of individuals observed belonged to vascular plants, freshwater decapod introduced species, with more native species crustaceans, phasmids, butterflies, freshwater expected to be extirpated from the site in the fish, amphibians, reptiles, birds, and mammals. future through competition and predation. This They found that overall, 28% of original species study shows that small fragments decline in their were lost in Singapore, probably due to value for forest birds over time. deforestation. Extinctions were higher Box 2.1 Figure Green broadbill. Photograph by Haw Chuan Lim. continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 56. 1 BIODIVERSITY 41 Box 2.1 (Continued) The old species inventories not only help in also be included in these as such can be understanding species losses but also help used to determine the effect of abundance determine the characteristics of species that are on species persistence. All these checklists vulnerable to habitat perturbations. Koh et al. should be placed on the web for wide (2004) compared ecological traits (e.g. body dissemination. Remember, like antiques, size) between extinct and extant butterflies in species inventories become more valuable Singapore. They found that butterflies species with time. restricted to forests and those which had high larval host plant specificity were particularly vulnerable to extirpation. In a similar study, but REFERENCES on angiosperms, Sodhi et al. (2008) found Brook, B. W., Sodhi, N. S., and Ng, P. K. L. (2003). that plant species susceptible to habitat Catastrophic extinctions follow deforestation in disturbance possessed traits such as Singapore. Nature, 424, 420–423. dependence on forests and pollination by Koh, L. P., Sodhi, N. S., and Brook, B. W. (2004). Prediction mammals. These trait comparison studies may extinction proneness of tropical butterflies. Conservation assist in understanding underlying Biology, 18, 1571–1578. mechanisms that make species vulnerable to Sodhi, N.S., Lee, T. M., Koh, L. P., and Dunn, R. R. extinction and in preemptive identification (2005). A century of avifaunal turnover in a small of species at risk from extinction. tropical rainforest fragment. Animal Conservation, The above highlights the value of species 8, 217–222. inventories. I urge scientists and amateurs Sodhi, N. S., Koh, L. P., Peh, K. S.‐H. et al. (2008). to make species lists every time they visit a Correlates of extinction proneness in tropical angios- site. Data such as species numbers should perms. Diversity and Distributions, 14, 1–10.Summary · Biodiversity is variably distributed across· Biodiversity is the variety of life in all of its manymanifestations. the Earth, although some marked spatial gra- dients seem common to numerous higher taxonomic· This variety can usefully be thought of in terms ofthree hierarchical sets of elements, which capture groups. · The obstacles to an improved understanding of biodiversity are: (i) its sheer magnitude and com-different facets: genetic diversity, organismal diver- plexity; (ii) the biases of the fossil record and thesity, and ecological diversity.· There is by definition no single measure of biodi-versity, although two different kinds of measures apparent variability in rates of molecular evolution; (iii) the relative paucity of quantitative sampling over much of the planet; and (iv) that levels and(number and heterogeneity) can be distinguished.· Pragmatically, and rather restrictively, biodiver-sity tends in the main to be measured in terms of patterns of biodiversity are being profoundly al- tered by human activities.number measures of organismal diversity, and espe-cially species richness. Suggested reading· Biodiversity has been present for much of thehistory of the Earth, but the levels have changed · Gaston, K. J. and Spicer, J. I. (2004). Biodiversity: andramatically and have proven challenging to docu- introduction, 2nd edition. Blackwell Publishing, Oxford,ment reliably. UK.© Oxford University Press 2010. All rights reserved. For permissions please email:
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  • 59. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLRoger, A. J. and Hug, L. A. (2006). The origin and diversifi- Torsvik, V., Øvreås, L., and Thingstad, T. F. (2002). Pro- cation of eukaryotes: problems with molecular phyloge- karyotic diversity-magnitude, dynamics, and controlling nies and molecular clock estimation. Philosophical factors. Science, 296, 1064–1066. Transactions of the Royal Society of London B, 361, van Rootselaar, O. (1999). New birds for the world: 1039–1054. species discovered during 1980–1999. Birding World, 12,Rosing, M. T. and Frei, R. (2004). U-rich Archaean sea-floor 286–293. sediments from Greenland - indications of 3700 Ma van Rootselaar, O. (2002). New birds for the world: oxygenic photosynthesis. Earth and Planetary Science species described during 1999–2002. Birding World, Letters, 217, 237–244. 15, 428–431.Simpson, A. G. B. and Roger, A. J. (2004). The real ‘king- Venter, J. C., Remington, K., Heidelberg, J. F., et al. (2004). doms’ of eukaryotes. Current Biology, 14, R693–R696. Environment genome shotgun sequencing of theSpalding, M. D., Fox, H. E., Allen, G. R., et al. (2007). Marine Sargasso Sea. Science, 304, 66–74. ecoregions of the world: a bioregionalisation of coastal Voss, R. S. and Emmons, L. H. (1996). Mammalian diversity and shelf areas. BioScience, 57, 573–583. in Neotropical lowland rainforests: a preliminaryStraatsma, G. and Krisai-Greilhuber, I. (2003). Assemblage assessment. Bulletin of the American Museum of Natural structure, species richness, abundance and distribution History, 230, 1–115. of fungal fruit bodies in a seven year plot-based survey Ward, B. B. (2002). How many species of prokaryotes are near Vienna. Mycological Research, 107, 632–640. there? Proceedings of the National Academy of Sciences of theTerborgh, J., Robinson, S. K., Parker, T. A. III, Munn, C. A., United States of America, 99, 10234–10236. and Pierpont, N. (1990). Structure and organization White, D. C., Phelps, T. J., and Onstott, T. C. (1998). What’s of an Amazonian forest bird community. Ecological up down there? Current Opinion in Microbiology, Monographs, 60, 213–238. 1, 286–290.Thomas, G. H., Orme, C. D., Davies, R. G., et al. (2008). Whitman, W. B., Coleman, D. C., and Wiebe, W. J. (1998). Regional variation in the historical components of global Prokaryotes: the unseen majority. Proceedings of the avian species richness. Global Ecology and Biogeography, National Academy of Sciences of the United States of America, 17, 340–351. 95, 6578–6583.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 60. 1 CHAPTER 3 Ecosystem functions and services Cagan H. SekerciogluIn our increasingly technological society, people may not know what an ecosystem is, the propergive little thought to how dependent they are on functioning of the world’s ecosystems is critical tothe proper functioning of ecosystems and the human survival, and understanding the basics ofcrucial services for humanity that flow from ecosystem services is essential. Entire volumesthem. Ecosystem services are “the conditions have been written on ecosystem services (Nation-and processes through which natural ecosystems, al Research Council 2005; Daily 1997), culminat-and the species that make them up, sustain and ing in a formal, in-depth, and global overview byfulfill human life” (Daily 1997); in other words, hundreds of scientists: the Millennium Ecosystem“the set of ecosystem functions that are useful to Assessment (2005a). It is virtually impossible to listhumans” (Kremen 2005). Although people have all the ecosystem services let alone the naturalbeen long aware that natural ecosystems help products that people directly consume, sosupport human societies, the explicit recognition this discussion presents a brief introduction toof “ecosystem services” is relatively recent ecosystem function and an overview of critical(Ehrlich and Ehrlich 1981a; Mooney and Ehrlich ecosystem services.1997). Since the entire planet is a vast network ofintegrated ecosystems, ecosystem services range 3.1 Climate and the Biogeochemical Cyclesfrom global to microscopic in scale (Table 3.1;Millennium Ecosystem Assessment 2005a). Ecosystem services start at the most fundamentalEcosystems purify the air and water, generate level: the creation of the air we breathe and theoxygen, and stabilize our climate. Earth would supply and distribution of water we drink.not be fit for our survival if it were not for plants Through photosynthesis by bacteria, algae,that have created and maintained a suitable at- plankton, and plants, atmospheric oxygen ismosphere. Organisms decompose and detoxify mostly generated and maintained by ecosystemsdetritus, preventing our civilization from being and their constituent species, allowing humansburied under its own waste. Other species help to and innumerable other oxygen-dependent organ-create the soils on which we grow our food, and isms to survive. Oxygen also enables the atmo-recycle the nutrients essential to agriculture. Myr- sphere to “clean” itself via the oxidation ofiad creatures maintain these soils, play key roles compounds such as carbon monoxide (Sodhiin recycling nutrients, and by so doing help to et al. 2007) and another form of oxygen in themitigate erosion and floods. Thousands of animal ozone layer, protects life from the sun’s carcino-species pollinate and fertilize plants, protect them genic, ultraviolet (UV) rays.from pests, and disperse their seeds. And of Global biogeochemical cycles consist of “thecourse, humans use and trade thousands of transport and transformation of substances inplant, animal and microorganism species for the environment through life, air, sea, land, andfood, shelter, medicinal, cultural, aesthetic and ice” (Alexander et al. 1997). Through these cycles,many other purposes. Although most people the planet’s climate, ecosystems, and creatures 45© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 61. Table 3.1 Ecosystem services, classified according to the Millennium Ecosystem Assessment (2003), and their ecosystem service providers. ‘Functionalunits’ refer to the unit of study for assessing functional contributions (∫ik) of ecosystem service providers; spatial scale indicates the scale(s) of operationof the service. Assessment of the potential to apply this conceptual framework to the service is purposefully conservative and is based on the degree towhich the contributions of individual species or communities can currently be quantified (Kremen 2005). Potential to apply this conceptual Ecosystem service providers/ framework forService trophic level Functional units Spatial scale ecological studyAesthetic, cultural All biodiversity Populations, Local‐global Low species, communities, ecosystemsEcosystem goods Diverse species Populations, Local‐global Medium species, communities, ecosystemsUV protection Biogeochemical cycles, micro‐ Biogeochemical Global Low organisms, plants cycles, functional groupsPurification Micro‐organisms, plants Biogeochemical Regional‐ Medium (plants) of air cycles, global populations, species, functional groupsFlood mitigation Vegetation Communities, Local‐regional Medium habitatsDrought mitigation Vegetation Communities, Local‐regional Medium habitatsClimate stability Vegetation Communities, Local‐global Medium habitatsPollination Insects, birds, mammals Populations, Local High species, functional groupsPest control Invertebrate parasitoids and Populations, Local High predators and vertebrate predators species, functional groupsPurification of water Vegetation, soil micro‐organisms, Populations, Local‐regional Medium to high* aquatic micro‐organisms, aquatic species, invertebrates functional groups, communities, habitatsDetoxification and Leaf litter and soil invertebrates, soil Populations, Local‐regional Medium decomposition of micro‐organisms, aquatic micro‐ species, wastes organisms functional groups, communities, habitatsSoil generation and Leaf litter and soil invertebrates, soil Populations, Local Medium soil fertility micro‐organisms, nitrogen‐fixing species, plants, plant and animal functional production of waste products groupsSeed dispersal Ants, birds, mammals Populations, Local High species, functional groups* Waste‐water engineers ‘design’ microbial communities; in turn, wastewater treatments provide ideal replicated experimentsfor ecological work (Graham and Smith 2004 in Kremen 2005).
  • 62. 1 ECOSYSTEM FUNCTIONS AND SERVICES 47are tightly linked. Changes in one component can and warming both exacerbate the problem as for-have drastic effects on another, as exemplified by est ecosystems switch from being major carbonthe effects of deforestation on climatic change sinks to being carbon sources (Phat et al. 2004;(Phat et al. 2004). The hydrologic cycle is one IPCC 2007). If fossil fuel consumption and defor-that most immediately affects our lives and it is estation continue unabated, global CO2 emissionstreated separately below. are expected to be about 2–4 times higher than at As carbon-based life forms, every single organ- present by the year 2100 (IPCC 2007). As climateism on our planet is a part of the global carbon and life have coevolved for billions of years andcycle. This cycle takes place between the four main interact with each other through various feedbackreservoirs of carbon: carbon dioxide (CO2) in the mechanisms (Schneider and Londer 1984), rapidatmosphere; organic carbon compounds within climate change would have major consequencesorganisms; dissolved carbon in water bodies; and for the planet’s life-support systems. There arecarbon compounds inside the earth as part of soil, now plans under way for developed nations tolimestone (calcium carbonate), and buried organic finance the conservation of tropical forests in thematter like coal, natural gas, peat, and petroleum developing world so that these forests can contin-(Alexander et al. 1997). Plants play a major role in ue to provide the ecosystem service of acting asfixing atmospheric CO2 through photosynthesis carbon sinks (Butler 2008).and most terrestrial carbon storage occurs in forest Changes in ecosystems affect nitrogen, phos-trees (Falkowski et al. 2000). The global carbon phorus, and sulfur cycles as well (Alexander et al.cycle has been disturbed by about 13% compared 1997; Millennium Ecosystem Assessment 2005b;to the pre-industrial era, as opposed to 100% or Vitousek et al. 1997). Although nitrogen in itsmore for nitrogen, phosphorous, and sulfur cycles gaseous form (N2) makes up 80% of the atmo-(Falkowski et al. 2000). Given the dominance of sphere, it is only made available to organismscarbon in shaping life and in regulating climate, through nitrogen fixation by cyanobacteria inhowever, this perturbation has already been aquatic systems and on land by bacteria andenough to lead to significant climate change with algae that live in the root nodules of lichens andworse likely to come in the future [IPCC (Intergov- legumes (Alexander et al. 1997). Eighty millionernmental Panel on Climate Change) 2007]. tons of nitrogen every year are fixed artificially Because gases like CO2, methane (CH4), and by industry to be used as fertilizer (Millenniumnitrous oxide (N2O) trap the sun’s heat, especially Ecosystem Assessment 2005b). However, the ex-the long-wave infrared radiation that’s emitted by cessive use of nitrogen fertilizers can lead to nu-the warmed planet, the atmosphere creates a nat- trient overload, eutrophication, and eliminationural “greenhouse” (Houghton 2004). Without this of oxygen in water bodies. Nitrogen oxides,greenhouse effect, humans and most other organ- regularly produced as a result of fossil fuel com-isms would be unable to survive, as the global bustion, are potent greenhouse gases thatmean surface temperature would drop from the increase global warming and also lead to smog,current 14 C to –19 C (IPCC 2007). Ironically, breakdown of the ozone layer, and acid rainthe ever-rising consumption of fossil fuels during (Alexander et al. 1997). Similarly, although sulfurthe industrial age and the resultant increasing is an essential element in proteins, excessiveemission of greenhouse gases have created the sulfur emissions from human activities lead toopposite problem, leading to an increase in the sulfuric acid smog and acid rain that harms peo-magnitude of the greenhouse effect and a conse- ple and ecosystems alike (Alexander et al. 1997).quent rise in global temperatures (IPCC 2007). Phosphorous (P) scarcity limits biological nitro-Since 1750, atmospheric CO2 concentrations gen fixation (Smith 1992). In many terrestrial eco-have increased by 34% (Millennium Ecosystem systems, where P is scarce, specialized symbioticAssessment 2005a) and by the end of this century, fungi (mycorrhizae) facilitate P uptake by plantsaverage global temperature is projected to rise by (Millennium Ecosystem Assessment 2005b). Even1.8 –6.4 C (IPCC 2007). Increasing deforestation though P is among the least naturally available of© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 63. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLmajor nutrients, use of phosphorous in artificial (2007): improvement of extractive water supply,fertilizers and runoff from animal husbandry improvement of in-stream water supply, wateroften also leads to eutrophication in aquatic sys- damage mitigation, provision of water-relatedtems (Millenium Ecosystem Assessment 2005b). cultural services, and water-associated support-The mining of phosphate deposits and their addi- ing services (Figure 3.1). Although 71% of thetion to terrestrial ecosystems as fertilizers repre- planet is covered by water, most of this is seawa-sents a six fold increase over the natural rate of ter unfit for drinking or agriculture (Postel et al.mobilization of P by the weathering of phosphate 1996). Fresh water not locked away in glaciersrock and by plant activity (Reeburgh 1997). and icecaps constitutes 0.77% of the planet’sP enters aquatic ecosystems mainly through ero- water (Shiklomanov 1993). To provide sufficientsion, but no-till agriculture and the use of hedge- fresh water to meet human needs via industrialrows can substantially reduce the rate of this desalination (removing the salt from seawater)process (Millenium Ecosystem Assessment 2005a). would cost US$3 000 billion per year (Postel and Carpenter 1997). Quantity, quality, location, and timing of water provision determine the scale and impact of3.2 Regulation of the Hydrologic Cycle hydrologic services (Brauman et al. 2007). TheseOne of the most vital and immediate services of attributes can make the difference between waterecosystems, particularly of forests, rivers and as a blessing (e.g. drinking water) or a curse (e.g.wetlands, is the provisioning and regulation of floods). Water is constantly redistributed throughwater resources. These services provide a vast the hydrologic cycle. Fresh water comes downrange of benefits from spiritual to life-saving, as precipitation, collects in water bodies or isillustrated by the classification of hydrologic ser- absorbed by the soil and plants. Some of thevices into five broad categories by Brauman et al. water flows unutilized into the sea or seeps into Ecohydrologic process Hydrologic attribute Hydrologic service (what the ecosystem does) (direct effect of the ecosystem) (what the beneficiary receives) Local climate interactions Quantity (surface and ground water Diverted water supply: Water use by plants storage and flow) water for municipal, agricultural, commercial, industrial, thermoelectric power Environmental filtration generation uses Quality In situ water supply: Soil stabilization (pathogens, nutrients, salinity, sediment) water for hydropower, recreation, transportation, Chemical and biological supply of fish and other additions/subtractions freshwater products Water damage mitigation: Soil development water for hydropower, Ground surface Location recreation, transportation, modification (ground/surface, supply of fish and other up/downstream, in/out of freshwater products Surface flow path alteration channel) Spiritual and aesthetic: River bank development provision of religious, educational, tourism values Supporting: Control of flow speed Water and nutrients to support Timing vital estuaries and other Short-and long-term water (peak flows, base flows, habitats, preservation of storage velocity) options Seasonality of water useFigure 3.1 The effects of hydrological ecosystem processes on hydrological services. Reprinted from Brauman et al. (2007).© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 64. 1 ECOSYSTEM FUNCTIONS AND SERVICES 49underground aquifers where it can remain for extent (Day et al. 2007). The impact of the 24millennia unless extracted by people; mining this December 2004 tsunami in Southeast Asia“fossil” groundwater is often unsustainable and is would have been reduced if some of the hard-a serious problem in desert regions like Libya est-hit areas had not been stripped of their man-(Millennium Ecosystem Assessment 2005c). The grove forests (Dahdouh-guebas et al. 2005;cycle is completed when water vapor is released Danielsen et al. 2005). These observations supportback into the atmosphere either through evapora- analytical models in which thirty “waru” treestion from land and water bodies or by being re- (Hibiscus tiliaceus) planted along a 100 m byleased from plants (transpiration) and other 1 meter band reduced the impact of a tsunamiorganisms. Rising environmental temperatures by 90% (Hiraishi and Harada 2003), a solutionare expected to increase evaporation and conse- more effective and cheaper than artificial barriers.quent precipitation in some places and raise the Hydrologic regulation by ecosystems beginslikelihood of droughts and fires in other places, with the first drop of rain. Vegetation layers,both scenarios that would have major conse- especially trees, intercept raindrops, which grad-quences for the world’s vegetation (Wright ually descend into the soil, rather than hitting it2005). These changes in turn can lead to further directly and leading to erosion and floods. Byclimatic problems, affecting agriculture and com- intercepting rainfall and promoting soil develop-munities worldwide. Ecosystems, particularly ment, vegetation can modulate the timing offorests, play major roles in the regulation of the flows and potentially reduce flooding. Flood mit-hydrologic cycle and also have the potential to igation is particularly crucial in tropical areasmoderate the effects of climate change. Tropical where downpours can rapidly deposit enormousforests act as heat and humidity pumps, transfer- amounts of water that can lead to increased ero-ring heat from the tropics to the temperate zones sion, floods, and deaths if there is little naturaland releasing water vapor that comes back as forest to absorb the rainfall (Bradshaw et al. 2007).rain (Sodhi et al. 2007). Extensive tropical defores- Studies of some watersheds have shown that na-tation is expected to lead to higher temperatures, tive forests reduced flood risks only at smallreduced precipitation, and increased frequency of scales, leading some hydrologists to question di-droughts and fires, all of which are likely to reduce rectly connecting forest cover to flood reductiontropical forest cover in a positive feedback loop (Calder and Aylward 2006). However, in the first(Sodhi et al. 2007). global-scale empirical demonstration that forests Forest ecosystems alone are thought to regulate are correlated with flood risk and severity inapproximately a third of the planet’s watersheds developing countries, Bradshaw et al. (2007) esti-on which nearly five billion people rely (Millen- mated that a 10% decrease in natural forest areanium Ecosystem Assessment 2005c). With in- would lead to a flood frequency increase betweencreasing human population and consequent 4% and 28%, and to a 4–8% increase in total floodwater pollution, fresh water is becoming an in- duration at the country scale. Compared to natu-creasingly precious resource, especially in arid ral forests, however, afforestation programs orareas like the Middle East, where the scarcity of forest plantations may not reduce floods, or maywater is likely to lead to increasing local conflicts even increase flood volume due to road construc-in the 21st century (Klare 2001; Selby 2005). tion, soil compaction, and changes in drainageAquatic ecosystems, in addition to being vital regimes (Calder and Aylward 2006). Non-nativesources of water, fish, waterfowl, reeds, and plantations can do more harm than good, partic-other resources, also moderate the local climate ularly when they reduce dry season water flowsand can act as buffers for floods, tsunamis, and (Scott et al. 2005).other water incursions (Figure 3.1). For example, Despite covering only 6% of the planet’s sur-the flooding following Hurricane Katrina would face, tropical forests receive nearly half of thehave done less damage if the coastal wetlands world’s rainfall, which can be as much as 22 500surrounding New Orleans had had their original mm during five months of monsoon season in© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 65. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLIndia (Myers 1997). In Southeast Asia, an intact farming can result in the loss of half the soilold-growth dipterocarp forest intercepts at least nutrients in less than a decade (Bolin and Cook35% of the rainfall, while a logged forest inter- 1983), a loss that can take centuries to restore. Incepts less than 20%, and an oil palm (Elaeis spp.) arid areas, the replacement of native deep-rootedplantation intercepts only 12% (Ba 1977). As a plants with shallow-rooted crop plants can leadconsequence, primary forest can moderate sea- to a rise in the water table, which can bring soilsonal extremes in water flow and availability bet- salts to the surface (salinization), cause waterlog-ter than more intensive land uses like plantation ging, and consequently result in crop lossesforestry and agriculture. For example, primary (Lefroy et al. 1993).forest in Ivory Coast releases three to five times Soil provides six major ecosystem servicesas much water at the end of the dry season com- (Daily et al. 1997):pared to a coffee plantation (Dosso 1981). How-ever, it is difficult to make generalizations about · · Moderating the hydrologic cycle. Physical support of plants.hydrologic response in the tropics. For example,local soil and rainfall patterns can result in a · · Retention and delivery of nutrients to plants. Disposal of wastes and dead organic matter.65-fold variation in tropical natural sedimentationrates (Bruijnzeel 2004). This underlines the impor-tance of site-specific studies in the tropics, but · · Renewal of soil fertility. Regulation of major element cycles.most hydrologic studies of ecosystems have Every year enough rain falls to cover the planettaken place in temperate ecosystems (Brauman with one meter of water (Shiklomanov 1993), butet al. 2007). thanks to soil’s enormous water retention capacity, most of this water is absorbed and gradually released to feed plants, underground aquifers, and rivers. However, intensive cultivation, by low-3.3 Soils and Erosion ering soil’s organic matter content, can reduce thisWithout forest cover, erosion rates skyrocket, and capacity, leading to floods, erosion, pollution, andmany countries, especially in the tropics, lose further loss of organic matter (Pimentel et al. 1995).astounding amounts of soil to erosion. World- Soil particles usually carry a negative charge,wide, 11 million km2 of land (the area of USA which plays a critical role in delivering nutrientand Mexico combined) are affected by high rates cations (positively-charged ions) like Ca2þ, Kþ,of erosion (Millennium Ecosystem Assessment Naþ, NH4þ, and Mg2þ to plants (Daily et al.2005b). Every year about 75 billion tons of soil 1997). To deliver these nutrients without soilare thought to be eroded from terrestrial ecosys- would be exceedingly expensive as modern hy-tems, at rates 13–40 times faster than the average droponic (water-based) systems cost more thanrate of soil formation (Pimentel and Kounang US$250 000 per ha (Canada’s Office of Urban1998). Pimentel et al. (1995) estimated that in the Agriculture 2008; Avinash 2008). Soil is also criti-second half of the 20th century about a third of the cal in filtering and purifying water by removingworld’s arable land was lost to erosion. This contaminants, bacteria, and other impuritiesmeans losing vital harvests and income (Myers (Fujii et al. 2001). Soils harbor an astounding di-1997), not to mention losing lives to malnutrition versity of microorganisms, including thousandsand starvation. Soil is one of the most critical but of species of protozoa, antibiotic-producing bac-also most underappreciated and abused elements teria (which produce streptomycin) and fungiof natural capital, one that can take a few years to (producing penicillin), as well as myriad inverte-lose and millennia to replace. A soil’s character is brates, worms and algae (Daily et al. 1997). Thesedetermined by six factors: topography, the nature organisms play fundamental roles in decompos-of the parent material, the age of the soil, soil ing dead matter, neutralizing deadly pathogens,organisms and plants, climate, and human activi- and recycling waste into valuable nutrients. Justty (Daily et al. 1997). For example, in the tropics, the nitrogen fixed by soil organisms like© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 66. 1 ECOSYSTEM FUNCTIONS AND SERVICES 51Rhizobium bacteria amounts to about 100 million practices (Gomes et al. 2003) can lessen wind ero-metric tons per year (Schlesinger 1991). It would cost sion substantially. Montane areas are especiallyat least US$320 billon/year to replace natural nitro- prone to rapid erosion (Milliman and Syvitskigen fertilization with fertilizers (Daily et al. 1997). 1992), and revegetation programs are critical in As the accelerating release of CO2, N2O (Nitrous such ecosystems (Vanacker et al. 2007). Interest-Oxide), methane and other greenhouse gases in- ingly, soil carbon buried in deposits resultingcreasingly modifies climate (IPCC 2007), the soil’s from erosion, can produce carbon sinks that cancapacity to store these molecules is becoming even offset up to 10% of the global fossil fuel emissionsmore vital. Per area, soil stores 1.8 times the carbon of CO2 (Berhe et al. 2007). However, erosion alsoand 18 times the nitrogen that plants alone can lowers soil productivity and reduces the organicstore (Schlesinger 1991). For peatlands, soil carbon carbon returned to soil as plant residue (Gregor-storage can be 10 times greater than that stored by ich et al. 1998). Increasing soil carbon capacity bythe plants growing on it and peatland fires release 5–15% through soil-friendly tillage practices notmassive amounts of CO2 into the atmosphere only offsets fossil-fuel carbon emissions by a(Page and Rieley 1998). roughly equal amount but also increases crop Despite soil’s vital importance, 17% of the yields and enhances food security (Lal 2004).Earth’s vegetated land surface (Oldeman 1998) An increase of one ton of soil carbon pool inor 23% of all land used for food production degraded cropland soils may increase crop yield[FAO (Food and Agriculture Organization of the by 20 to 40 kilograms per ha (kg/ha) for wheat,United Nations) 1990] has experienced soil deg- 10 to 20 kg/ha for maize, and 0.5 to 1 kg/ha forradation since 1945. Erosion is the best-known cowpeas (Lal 2004).example of the disruption of the sedimentarycycle. Although erosion is responsible for releas-ing nutrients from bedrock and making them 3.4 Biodiversity and Ecosystem Functionavailable to plants, excessive wind and watererosion results in the removal of top soil, the loss The role of biodiversity in providing ecosystemof valuable nutrients, and desertification. The di- services is actively debated in ecology. The diver-rect costs of erosion total about US$250 billion per sity of functional groups (groups of ecologicallyyear and the indirect costs (e.g. siltation, obsoles- equivalent species (Naeem and Li 1997)), is ascence of dams, water quality declines) approxi- important as species diversity, if not more so (Kre-mately $150 billion per year (Pimentel et al. men 2005), and in most services a few dominant1995). Sufficient preventive measures would cost species seem to play the major role (Hooper et al.only 19% of this total (Pimentel et al. 1995). 2005). However, many other species are critical The loss of vegetative cover increases the ero- for ecosystem functioning and provide “insur-sional impact of rain. In intact forests, most rain ance” against disturbance, environmental change,water does not hit the ground directly and tree and the decline of the dominant species (Tilmanroots hold the soil together against being washed 1997; Ricketts et al. 2004; Hobbs et al. 2007). As foraway (Brauman et al. 2007), better than in logged many other ecological processes, it was Charlesforest or plantations (Myers 1997) where roads Darwin who first wrote of this, noting that severalcan increase erosion rates (Bruijnzeel 2004). The distinct genera of grasses grown together wouldexpansion of farming and deforestation have produce more plants and more herbage than adoubled the amount of sediment discharged single species growing alone (Darwin 1872).into the oceans. Coral reefs can experience high Many studies have confirmed that increased bio-mortality after being buried by sediment dis- diversity improves ecosystem functioning incharge (Pandolfi et al. 2003; Bruno and Selig plant communities (Naeem and Li 1997; Tilman2007). Wind erosion can be particularly severe in 1997). Different plant species capture differentdesert ecosystems, where even small increases in resources, leading to greater efficiency and highervegetative cover (Hupy 2004) and reduced tillage productivity (Tilman et al. 1996). Due to the© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 67. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL Box 3.1 The costs of large‐mammal extinctions Robert M. Pringle When humans alter ecosystems, large mammals are typically the first species to disappear. They are hunted for meat, hides, and horns; they are harassed and killed if they pose a threat; they require expansive habitat; and they are susceptible to diseases, such as anthrax, rinderpest, and distemper, that are spread by domestic animals. Ten thousand years ago, humans played at least a supporting, if not leading, role in extinguishing most of the large mammals in the Americas and Australia. Over the last 30 years, we have extinguished many large‐mammal populations (and currently threaten many more) in Africa and Asia—the two continents that still support diverse Box 3.1 Figure 1 White-footed mice (Peromyscus leucopus, shown assemblages of these charismatic creatures. with an engorged tick on its ear) are highly competent reservoirs for Lyme The ecological and economic consequences disease. When larger mammals disappear, mice often thrive, increasing of losing large‐mammal populations vary disease risk. Photograph courtesy of Richard Ostfeld Laboratory. depending on the location and the ecological role of the species lost. The loss of carnivores has induced trophic cascades: in the absence of top predators, herbivores can multiply and deplete the plants, which in turn drives down the density and the diversity of other species (Ripple and Beschta 2006). Losing large herbivores and their predators can have the opposite effect, releasing plants and producing compensatory increases in the populations of smaller herbivores (e.g. rodents: Keesing 2000) and their predators (e.g. snakes: McCauley et al. 2006). Such increases, while not necessarily detrimental Box 3.1 Figure 2 Ecotourists gather around a pair of lions in themselves, can have unpleasant consequences Tanzania’s Ngorongoro Crater. Ecotourism is one of the most (see below). powerful driving forces for biodiversity conservation, especially in Many species depend on the activities of tropical regions where money is short. But tourists must be managed particular large mammal species. Certain in such a way that they do not damage or deplete the very resources trees produce large fruits and seeds apparently they have traveled to visit. Photograph by Robert M. Pringle adapted for dispersal by large browsers These examples and others suggest that the (Guimarães et al. 2008). Defecation by large loss of large mammals may precipitate mammals deposits these seeds and provides extinctions of other taxa and the relationships food for many dung beetles of varying degrees of among them, thus decreasing the diversity of specialization. In East Africa, the disturbance both species and interactions. Conversely, caused by browsing elephants creates habitat protecting the large areas needed to conserve for tree‐dwelling lizards (Pringle 2008), while large mammals may often serve to conserve the the total loss of large herbivores dramatically greater diversity of smaller organisms—the altered the character of an ant‐plant symbiosis via so‐called umbrella effect. a complex string of species interactions The potential economic costs of losing large (Palmer et al. 2008). mammals also vary from place to place. Because continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 68. 1 ECOSYSTEM FUNCTIONS AND SERVICES 53 Box 3.1 (Continued) cattle do not eat many species of woody plants, rhinoceroses in Asia—could deal a crippling the loss of wildlife from rangelands can result in blow to efforts to salvage the greater portion bush encroachment and decreased pastoral of biodiversity. profitability. Because some rodents and their parasites are reservoirs and vectors of various human diseases, increases in rodent densities REFERENCES may increase disease transmission (Ostfeld and Guimarães, P. R. J., Galleti, M., and Jordano, P. (2008). Mills 2007; Box 3.1 Figure 1). Perhaps most Seed dispersal anachronisms: rethinking the fruits importantly, because large mammals form the extinct megafauna ate. PloS One, 3, e1745. basis of an enormous tourism industry, the loss Keesing, F. (2000). Cryptic consumers and the ecology of of these species deprives regions of an an African savanna. BioScience, 50, 205–215. important source of future revenue and foreign McCauley, D. J., Keesing, F., Young, T. P., Allan, B. F., and exchange (Box 3.1 Figure 2). Pringle, R. M. (2006). Indirect effects of large herbivores on Arguably, the most profound cost of losing snakes in an African savanna. Ecology, 87, 2657–2663. large mammals is the toll that it takes on our Ostfeld, R. S., and Mills, J. N. (2007). Social behavior, ability to relate to nature. Being large mammals demography, and rodent‐borne pathogens. In J. O. ourselves, we find it easier to identify and Wolff and P. W. Sherman, eds Rodent societies, sympathize with similar species—they behave pp. 478–486. University of Chicago Press, Chicago, IL. in familiar ways, hence the term “charismatic Palmer, T. M., Stanton, M. L., Young, T. P., et al. (2008). megafauna.” While only a handful of large Breakdown of an ant‐plant mutualism follows the loss of mammal species have gone globally extinct in large mammals from an African savanna. Science, 319, the past century, we are dismantling many 192–195. species population by population, pushing Pringle, R. M. (2008). Elephants as agents of habitat creation them towards extinction. At a time when we for small vertebrates at the patch scale. Ecology, 89, desperately need to mobilize popular support 26–33. for conservation, the loss over the next 50 years Ripple, W. J. and Beschta, R. L. (2006). Linking a cougar of even a few emblematic species—great apes decline, trophic cascade, and catastrophic regime shift in in central Africa, polar bears in the arctic, Zion National Park. Biological Conservation, 133, 397–408.“sampling-competition effect” the presence of (Macarthur 1955; Hooper et al. 2005; Vitousekmore species increases the probability of having and Hooper 1993; Worm et al. 2006).a particularly productive species in any given Greenhouse and field experiments have con-environment (Tilman 1997). Furthermore, differ- firmed that biodiversity does increase ecosystement species’ ecologies lead to complementary re- productivity, while reducing fluctuations in pro-source use, where each species grows best under a ductivity (Naeem et al. 1995; Tilman et al. 1996).specific range of environmental conditions, and Although increased diversity can increase thedifferent species can improve environmental con- population fluctuations of individual species, di-ditions for other species (facilitation effect; Hoop- versity is thought to stabilize overall ecosystemer et al. 2005). Consequently, the more complex an functioning (Chapin et al. 2000; Tilman 1996) andecosystem is, the more biodiversity will increase make the ecosystem more resistant to perturba-ecosystem function, as more species are needed to tions (Pimm 1984). These hypotheses have beenfully exploit the many combinations of environ- confirmed in field experiments, where species-mental variables (Tilman 1997). More biodiverse rich plots showed less yearly variation in produc-ecosystems are also likely to be more stable and tivity (Tilman 1996) and their productivity duringmore efficient due to the presence of more path- a drought year declined much less than species-ways for energy flow and nutrient recycling poor plots (Tilman and Downing 1994). Because© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 69. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL Box 3.2 Carnivore conservation Mark S. Boyce Predation by carnivores can alter prey invariably swift and involves killing those population abundance and distribution, and individuals responsible for the depredation, but these predator effects have been shown to furthermore such incidents of human influence many aspects of community ecology. predation usually result in fear‐driven Examples include the effect of sea otters that management actions that seldom consider the kill and eat sea urchins reducing their ecological significance of the carnivores in abundance and herbivory on the kelp forests question. that sustain diverse near‐shore marine Another consideration that often plays a communities of the North Pacific. Likewise, major role in carnivore conservation is public subsequent to wolf (see Box 3.2 Figure) opinion. Draconian methods for predator recovery in Yellowstone National Park (USA), control, including aerial gunning and poisoning elk have become preferred prey of wolves of wolves by government agencies, typically resulting in shifts in the distribution and meets with fierce public opposition. Yet, some abundance of elk that has released vegetation livestock ranchers and hunters lobby to have from ungulate herbivory with associated the carnivores eradicated. Rural people who increases in beavers, song birds, and other are at risk of depredation losses from carnivores plants and animals. usually want the animals controlled or Yet, carnivore conservation can be very eliminated, whereas tourists and broader challenging because the actions of carnivores publics usually push for protection of the often are resented by humans. Carnivores carnivores. depredate livestock or reduce abundance of Most insightful are programs that change wildlife valued by hunters thereby coming into human management practices to reduce the direct conflict with humans. Some larger species probability of conflict. Bringing cattle into of carnivores can prey on humans. Every year, areas where they can be watched during people are killed by lions in Africa, children are calving can reduce the probability that bears or killed by wolves in India, and people are killed or wolves will kill the calves. Ensuring that mauled by cougars and bears in western North garbage is unavailable to bears and other America (see also Box 14.3). Retaliation is large carnivores reduces the risk that carnivores will become habituated to humans and consequently come into conflict. Livestock ranchers can monitor their animals in back‐country areas and can dispose of dead animal carcasses to reduce the risk of depredation. Killing those individuals that are known to depredate livestock can be an effective approach because individuals sometimes learn to kill livestock whereas most carnivores in the population take only wild prey. Managing recreational access to selected trails and roads can be an effective tool for reducing conflicts between large carnivores and people. Finding socially acceptable methods of predator control whilst learning to live in proximity with large Box 3.2 Figure Grey wolf (Canis lupus). Photograph from www. carnivores is the key challenge for carnivore conservation.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 70. 1 ECOSYSTEM FUNCTIONS AND SERVICES 55more species do better at utilizing and recycling Although it makes intuitive sense that the spe-nutrients, in the long-term, species-rich plots are cies that dominate in number and/or biomass arebetter at reducing nutrient losses and maintain- more likely to be important for ecosystem func-ing soil fertility (Tilman et al. 1996; Vitousek and tion (Raffaelli 2004; Smith et al. 2004), in someHooper 1993). cases, even rare species can have a role, for Box 3.3 Ecosystem services and agroecosystems in a landscape context Teja Tscharntke Agroecosystems result from the transformation may encourage environment friendly of natural ecosystems to promote ecosystem agriculture. This is why governments services, which are defined as benefits people implement payment‐for‐ecosystem service obtain from ecosystems (MEA 2005). Major programs such as the agri‐environment challenges in managing ecosystem services are schemes in the European Community or the that they are not independent of each other Chinese programs motivated by large floods on and attempts to optimize a single service (e.g. the Yangtze River (Tallis et al. 2008). reforestation) lead to losses in other services In addition, conservation of most services (e.g. food production; Rodriguez et al. 2006). needs a landscape perspective. Agricultural Agroecosystems such as arable fields and land use is often focused on few species and grasslands are typically extremely open local processes, but in dynamic, human‐ ecosystems, characterized by high levels of dominated landscapes, only a diversity of input (e.g. labour, agrochemicals) and output insurance species may guarantee resilience, i.e. (e.g. food resources), while agricultural the capacity to re‐organize after disturbances management reduces structural complexity (see Box 3.3 Figure). Biodiversity and associated and associated biodiversity. ecosystem services can be maintained only in The world’s agroecosystems deliver a number complex landscapes with a minimum of near‐ of key goods and services valued by society such natural habitat (in central Europe roughly 20%) as food, feed, fibre, water, functional supporting a minimum number of species biodiversity, and carbon storage. These services dispersing across natural and managed systems may directly contribute to human well‐being, (Tscharntke et al. 2005). For example, pollen for example through food production, or just beetles causing economically meaningful indirectly through ecosystem processes such as damage in oilseed rape (canola) are naturally natural biological control of crop pests controlled by parasitic wasps in complex but (Tscharntke et al. 2007) or pollination of crops not in simplified landscapes. Similarly, high (Klein et al. 2007). Farmers are mostly levels of pollination and yield in coffee and interested in the privately owned, marketable pumpkin depend on a high diversity of bee goods and services, while they may also species, which is only available in produce public goods such as aesthetic heterogeneous environments. The landscape landscapes or regulated water levels. Finding context may be even more important for local win‐win solutions that serve both private biodiversity and associated ecosystem services economic gains in agroecosystems and public than differences in local management, for long‐term conservation in agricultural example between organic and conventional landscapes is often difficult (but see Steffan‐ farming or between crop fields with or without Dewenter et al. 2007). The goal of long‐lasting near‐natural field margins, because the ecosystem services providing sustainable organisms immigrating into agroecosystems human well‐being may become compromised from the landscape‐wide species pool may by the short‐term interest of farmers in compensate for agricultural intensification at a increasing marketable services, but incentives local scale (Tscharntke et al. 2005). continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 71. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL Box 3.3 (Continued) Disturbance a) d) b Y a Decreasing landscape Number of species b) e) Biological control complexity b Y a c) f) b Y a Box 3.3 Figure Hypothesized responses to disturbance on ecosystem services such as biological control and pollination by native natural enemies and pollinators in different landscapes, showing how beta diversity (a‐c) and recover of biological control and pollination after disturbance (d‐f) change with landscape heterogeneity. Adapted from Tscharntke et al. (2007). a) and d) Intensely used monotonous landscape with a small available species pool, giving a low general level of ecosystem services, a greater dip in the service after a disturbance and an ecosystem that is unable to recover. b) and e) Intermediate landscape harboring slightly higher species richness, rendering deeper dip and slower return from a somewhat lower maximum level of biological control or pollination after a disturbance. c) and f) Heterogeneous landscape with large species richness, mainly due to the higher beta diversity, rendering high maximum level of the service, and low dip and quick return after a disturbance. The turnover of species among patches (the high beta diversity coping with the spatial and dissimilarity of communities creating high beta temporal heterogeneity in a real world under diversity, in contrast to the local, patch‐level Global Change. alpha diversity) is the dominant driver of landscape‐wide biodiversity. Beta diversity reflects the high spatial and temporal REFERENCES heterogeneity experienced by communities at a landscape scale. Pollinator or biocontrol species Klein, A.‐M., Vaissière, B. E., Cane. J. H., et al. (2007). that do not contribute to the service in one patch Importance of pollinators in changing landscapes for may be important in other patches, providing world crops. Proceedings of the Royal Society of London spatial insurance through complementary B, 274, 303–313. resource use (see Box 3.3 Figure). Sustaining MEA (2005). Millenium Ecosystem Assessment. Island ecosystem services in landscapes depends on a Press, Washington, DC. continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 72. 1 ECOSYSTEM FUNCTIONS AND SERVICES 57 Box 3.3 (Continued) Rodriguez, J. J., Beard, T. D. Jr, Bennett, E. M., et al. (2006). practical conservation and economic development. Trade‐offs across space, time, and ecosystem services. Proceedings of the National Academy of Sciences of the Ecology and Society, 11, 28 (online). United States of America, 105, 9457–9464. Steffan‐Dewenter, I., Kessler, M., Barkmann, J., et al. Tscharntke, T., Klein, A.‐M., Kruess, A., Steffan‐Dewen- (2007). Tradeoffs between income, biodiversity, and ter, I, and Thies, C. (2005). Landscape perspectives on ecosystem functioning during tropical rainforest con- agricultural intensification and biodiversity ‐ ecosystem version and agroforestry intensification. Proceedings of service management. Ecology Letters, 8, 857–874. the National Academy of Sciences of the United States Tscharntke, T., Bommarco, R., Clough, Y., et al. (2007). of America, 104, 4973–4978 Conservation biological control and enemy Tallis, H., Kareiva, P., Marvier, M., and Chang, A. (2008). diversity on a landscape scale. Biological Control, An ecosystem services framework to support both 43, 294–309.example, in increasing resistance to invasion increasingly vital over the entire range of habitats(Lyons and Schwartz 2001). A keystone species and systems, from diverse forest stands seques-is one that has an ecosystem impact that is dis- tering CO2 better in the long-term (Bolker et al.proportionately large in relation to its abundance 1995; Hooper et al. 2005; but see Tallis and Kar-(Hooper et al. 2005; Power et al. 1996; see Boxes eiva 2006) to forest-dwelling native bees’ coffee3.1, 3.2, and 5.3). Species that are not thought of as pollination services increasing coffee production“typical” keystones can turn out to be so, some- in Costa Rica (Ricketts et al. 2004; also see Boxtimes in more ways than one (Daily et al. 1993). 3.3). With accelerating losses of unique species,Even though in many communities only a few humanity, far from hedging its bets, is movingspecies have strong effects, the weak effects of ever closer to the day when we will run out ofmany species can add up to a substantial stabiliz- options on an increasingly unstable effect and seemingly “weak” effects overbroad scales can be strong at the local level (Ber-low 1999). Increased species richness can “insure” 3.5 Mobile Linksagainst sudden change, which is now a globalphenomenon (Parmesan and Yohe 2003; Root “Mobile links” are animal species that provideet al. 2003). Even though a few species may critical ecosystem services and increase ecosys-make up most of the biomass of most functional tem resilience by connecting habitats and ecosys-groups, this does not mean that other species are tems as they move between them (Gilbert 1980;unnecessary (Walker et al. 1999). Species may act Lundberg and Moberg 2003; Box 3.4). Mobilelike the rivets in an airplane wing, the loss of each links are crucial for maintaining ecosystem func-unnoticed until a catastrophic threshold is passed tion, memory, and resilience (Nystrm and Folke(Ehrlich and Ehrlich 1981b). 2001). The three main types of mobile links: ge- As humanity’s footprint on the planet increases netic, process, and resource links (Lundberg andand formerly stable ecosystems experience con- Moberg 2003), encompass many fundamentalstant disruptions in the form of introduced spe- ecosystem services (Sekercioglu 2006a, 2006b).cies (Chapter 7), pollution (Box 13.1), climate Pollinating nectarivores and seed dispersing fru-change (Chapter 8), excessive nutrient loads, givores are genetic links that carry genetic mate-fires (Chapter 9), and many other perturbations, rial from an individual plant to another plant orthe insurance value of biodiversity has become to a habitat suitable for regeneration, respectively© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 73. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL Box 3.4 Conservation of plant‐animal mutualisms Priya Davidar Plant‐animal mutualisms such as pollination abiotic means increase in the community (Wright and seed dispersal link plant productivity and et al. 2007b). ecosystem functioning, and maintain gene flow Habitat fragmentation is another process that in plant populations. Insects, particularly bees, can disrupt mutualistic interactions by reducing are the major pollinators of wild and crop the diversity and abundance of pollinators and plants worldwide, whereas vertebrates such as seed dispersal agents, and creating barriers to birds and mammals contribute pollen and seed dispersal (Cordeiro and Howe disproportionately to dispersal of seeds. About 2001, 2003; Aguilar et al. 2006). 1200 vertebrate and 100 000 invertebrate Plant‐animal mutualisms form webs or species are involved in pollination (Roubik networks that contribute to the maintenance of 1995; Buchmann and Nabhan 1996). Pollinators biodiversity. Specialized interactions tend to be are estimated to be responsible for 35% of nested within generalized interactions where global crop production (Klein et al. 2007) and generalists interact more with each other than by for 60–90% of the reproduction of wild plants chance, whereas specialists interact with (Kremen et al. 2007). It is estimated that feral generalists (Bascompte and Jordano 2006). and managed honey bee colonies have Interactions are usually asymmetric, where one declined by 25% in the USA since the 1990s, partner is more dependent on the other than vice‐ and globally about 200 species of wild versa. These characteristics allow for the vertebrate pollinators might be on the verge of persistence of rare specialist species. Habitat loss extinction (Allen‐Wardell et al. 1998). The and fragmentation (Chapters 4 and 5), hunting widespread decline of pollinators and (Chapter 6) and other factors can disrupt consequently pollination services is a cause for mutualistic networks and result in loss of concern and is expected to reduce crop biodiversity. Models suggest that structured productivity and contribute towards loss of networks are less resilient to habitat loss than biodiversity in natural ecosystems (Buchmann randomly generated communities (Fortuna and and Nabhan 1996; Kevan and Viana 2003). Bascompte 2006). Habitat loss, modification and the Therefore maintenance of contiguous forests indiscriminate use of pesticides are cited as and intact functioning ecosystems is needed to major reasons for pollinator loss (Kevan and sustain mutualistic interactions such as Viana 2003). This alarming trend has led to the pollination and seed dispersal. For agricultural creation of an “International Initiative for the production, wild biodiversity needs to be Conservation and Sustainable use of preserved in the surrounding matrix to Pollinators” as a key element under the promote native pollinators. Convention on Biodiversity, and the International Union for the Conservation of REFERENCES Nature has a task force on declining pollination in the Survival Service Commission. Aguilar, R., Ashworth, L., Galetto, L., and Aizen, M. A. Frugivores tend to be less specialized than (2006). Plant reproductive susceptibility to habitat frag- pollinators since many animals include some fruit mentation: review and synthesis through a meta‐analy- in their diet (Wheelwright and Orians 1982). sis. Ecology Letters 9, 968–980. Decline of frugivores from overhunting and loss Allen‐Wardell, G., Bernhardt, P., Bitner, R., et al. (1998). of habitat, can affect forest regeneration The potential consequences of pollinator declines on the (Wright et al. 2007a). Hunting pressure conservation of biodiversity and stability of food crop differentially affects recruitment of species, yields. Conservation Biology, 12, 8–17. where seeds dispersed by game animals Bascompte, J. and Jordano, P. (2006). The structure of decrease, and small non‐game animals and by plant‐animal mutualistic networks. In M. Pascual and continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 74. 1 ECOSYSTEM FUNCTIONS AND SERVICES 59 Box 3.4 (Continued) J. Dunne, eds Ecological networks, pp. 143–159. Oxford world crops. Proceedings of the Royal Society of London University Press, Oxford, UK. B, 274, 303–313. Buchmann, S. L. and Nabhan, G. P. (1996). The forgotten Kremen, C., Williams, N. M., Aizen, M. A., et al. (2007). pollinators. Island Press, Washington, DC. Pollination and other ecosystem services produced by Cordeiro, N. J. and Howe, H. F. (2001). Low recruitment of mobile organisms: a conceptual framework for the trees dispersed by animals in African forest fragments. effects of land‐use change. Ecology Letters, 10, 299–314. Conservation Biology, 15, 1733–1741. Roubik, D. W. (1995). Pollination of cultivated plants in the Cordeiro, N. J. and Howe, H. F. (2003). Forest fragmenta- tropics. Bulletin 118. FAO, Rome, Italy. tion severs mutualism between seed dispersers and an Wheelwright, N. T. and Orians, G. H. (1982). Seed dispersal endemic African tree. Proceedings of the National by animals: contrasts with pollen dispersal, problems of Academy of Sciences of the United States of America, terminology, and constraints on coevolution. American 100, 14052–14056. Naturalist, 119, 402–413. Fortuna, M. A. and Bascompte, J. (2006). Habitat loss and Wright, S. J., Hernandez, A., and Condit, R. (2007a). The the structure of plant‐animal mutualistic networks. bushmeat harvest alters seedling banks by favoring Ecology Letters, 9, 281–286. lianas, large seeds and seeds dispersed by bats, birds Kevan, P. G. and Viana, B. F. (2003). The global decline of and wind. Biotropica, 39, 363–371. pollination services. Biodiversity, 4, 3–8. Wright, S. J., Stoner, K. E., Beckman, N., et al. (2007b). The Klein, A‐M., Vaissiere, B. E., Cane, J. H., et al. (2007). plight of large animals in tropical forests and the conse- Importance of pollinators in changing landscapes for quences for plant regeneration. Biotropica, 39, 289–291.(Box 3.4). Trophic process links are grazers, such influence one another (Lundberg and Mobergas antelopes, and predators, such as lions, bats, 2003). The long-distance migrations of manyand birds of prey that influence the populations species, such as African antelopes, songbirds,of plant, invertebrate, and vertebrate prey (Boxes waterfowl, and gray whales (Eschrichtius robustus)3.1 and 3.2). Scavengers, such as vultures, are are particularly important examples of criticalcrucial process links that hasten the decomposi- mobile links. However, many major migrationstion of potentially disease-carrying carcasses are disappearing (Wilcove 2008) and nearly(Houston 1994). Predators often provide natural two hundred migratory bird species are threatenedpest control (Holmes et al. 1979). Many animals, or near threatened with extinction (Sekercioglusuch as fish-eating birds that nest in colonies, are 2007).resource links that transport nutrients in their Dispersing seeds is among the most importantdroppings and often contribute significant re- functions of mobile links. Vertebrates are the mainsources to nutrient-deprived ecosystems (Ander- seed vectors for flowering plants (Regal 1977; Tiff-son and Polis 1999). Some organisms like ney and Mazer 1995), particularly woody specieswoodpeckers or beavers act as physical process (Howe and Smallwood 1982; Levey et al. 1994;linkers or “ecosystem engineers” ( Jones et al. Jordano 2000). This is especially true in the tropics1994). By building dams and flooding large where bird seed dispersal may have led to theareas, beavers engineer ecosystems, create new emergence of flowering plant dominance (Regalwetlands, and lead to major changes in species 1977; Tiffney and Mazer 1995). Seed dispersal iscomposition (see Chapter 6). In addition to con- thought to benefit plants in three major wayssuming insects (trophic linkers), many wood- (Howe and Smallwood 1982):peckers also engineer their environment andbuild nest holes later used by a variety of otherspecies (Daily et al. 1993). Through mobile links, · Escape from density-dependent mortality caused by pathogens, seed predators, competitors, and her-distant ecosystems and habitats are linked to and bivores (Janzen-Connell escape hypothesis).© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 75. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL· Chance colonization of favorable but unpredict-able sites via wide dissemination of seeds. the world’s flowering plant species and three quarters of food crops (Nabhan and Buchmann· Directed dispersal to specific sites that are partic-ularly favorable for establishment and survival. 1997), are the most important group of pollina- tors (Box 3.3). In California alone, their services are estimated to be worth $4.2 billion (Brauman Although most seeds are dispersed over short and Daily 2008). However, bee numbers world-distances, long-distance dispersal is crucial (Cain wide are declining (Nabhan and Buchmann 1997)et al. 2000), especially over geological time scales (Box 3.5). In addition to the ubiquitous Europeanduring which some plant species have been calcu- honeybee (Apis mellifera), native bee species thatlated to achieve colonization distances 20 times depend on natural habitats also provide valuablehigher than would be possible without vertebrate services to farmers, exemplified by Costa Ricanseed dispersers (Cain et al. 2000). Seed dispersers forest bees whose activities increase coffee yieldplay critical roles in the regeneration and restora- by 20% near forest fragments (Ricketts et al. 2004).tion of disturbed and degraded ecosystems (Wun- Some plant species mostly depend on a singlederle 1997; Chapter 6), including newly-formed (Parra et al. 1993) or a few (Rathcke 2000) pollinatorvolcanic soils (Nishi and Tsuyuzaki 2004). species. Plants are more likely to be pollinator-lim- Plant reproduction is particularly pollination- ited than disperser-limited (Kelly et al. 2004) and alimited in the tropics relative to the temperate survey of pollination experiments for 186 specieszone (Vamosi et al. 2006) due to the tropics great- showed that about half were pollinator-limiteder biodiversity, and up to 98% of tropical rain- (Burd 1994). Compared to seed dispersal, pollina-forest trees are pollinated by animals (Bawa tion is more demanding due to the faster ripening1990). Pollination is a critical ecosystem function rates and shorter lives of flowers (Kelly et al. 2004).for the continued persistence of the most biodi- Seed disperser and pollinator limitation are oftenverse terrestrial habitats on Earth. Nabhan and more important in island ecosystems with fewerBuchmann (1997) estimated that more than 1200 species, tighter linkages, and higher vulnerabilityvertebrate and about 289 000 invertebrate species to disturbance and introduced species. Island plantare involved in pollinating over 90% of flowering species are more vulnerable to the extinctions ofplant species (angiosperms) and 95% of food their pollinators since many island plants have lostcrops. Bees, which pollinate about two thirds of Box 3.5 Consequences of pollinator decline for the global food supply Claire Kremen Both wild and managed pollinators have extreme risk of relying on a single pollinator to suffered significant declines in recent years. provide services for the world’s crop species. Managed Apis mellifera, the most important Seventy‐five percent of globally important source of pollination services for crops around crops rely on animal pollinators, providing up the world, have been diminishing around the to 35% of crop production (Klein et al. 2007). globe (NRC 2006), particularly in the US where At the same time, although records are sorely colony numbers are now at 50% of their 1950 lacking for most regions, comparisons of recent levels. In addition, major and extensive colony with historical (pre‐1980) records have losses have occurred over the past several years indicated significant regional declines in species in North America and Europe, possibly due to richness of major pollinator groups (bees and diseases as well as other factors (Cox‐Foster hoverflies in Britain; bees alone in the et al. 2007; Stokstad 2007), causing shortages Netherlands) (Biesmeijer et al. 2006). Large and rapid increases in the price of pollination reductions in species richness and abundance of services (Sumner and Boriss 2006). These recent bees have also been documented in regions of trends in honey bee health illustrate the high agricultural intensity in California’s continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 76. 1 ECOSYSTEM FUNCTIONS AND SERVICES 61 Box 3.5 (Continued) Central Valley (Kremen et al. 2002; Klein and reasons, we may indeed face more serious Kremen unpublished data). Traits associated shortages of pollinators in the future. with bee, bumble bee and hoverfly declines in A recent, carefully analyzed, global assessment Europe included floral specialization, slower of the economic impact of pollinator loss (e.g. (univoltine) development and lower dispersal total loss of pollinators worldwide) estimates our (non‐migratory) species (Biesmeijer et al. 2006; vulnerability (loss of economic value) at Euro 153 Goulson et al. 2008). Specialization is also billion or 10% of the total economic value of indicated as a possible correlate of local annual crop production (Gallai et al. 2009). extinction in pollinator communities studied Although total loss of pollination services is both across a disturbance gradient in Canada; unlikely to occur and to cause widespread famine communities in disturbed habitat contained if it were to occur, it potentially has both serious significantly more generalized species than economic and human health consequences. For those associated with pristine habitats (Taki example, some regions of the world produce and Kevan 2007). Large‐bodied bees were more large proportions of the world’s pollinator‐ sensitive to increasing agricultural dependent crops—such regions would intensification in California’s Central Valley, experience more severe economic consequences and ominously, bees with the highest per‐visit from the loss of pollinators, although growers pollination efficiencies were also most likely to and industries would undoubtedly quickly go locally extinct with agricultural respond to these changes in a variety of ways intensification (Larsen et al. 2005). passing the principle economic burden on to Thus, in highly intensive farming regions, consumers globally (Southwick and Southwick such as California’s Central Valley, that 1992; Gallai et al. 2009). Measures of the impacts contribute comparatively large amounts to on consumers (consumer surplus) are of the same global food production (e.g. 50% of the world order of magnitude (Euro 195–310 billion based supply of almonds), the supply of native bee on reasonable estimates for price elasticities, pollinators is lowest in exactly the regions Gallai et al. 2009) as the impact on total economic where the demand for pollination services is value of crop production. Nutritional highest. Published (Kremen et al. 2002) and consequences may be more fixed and more recent studies (Klein et al. unpublished data) serious than economic consequences, due to the clearly show that the services provided by wild likely plasticity of responses to economic change. bee pollinators are not sufficient to meet the Pollinator‐dependent crop species supply not only demand for pollinators in these intensive up to 35% of crop production by weight (Klein regions; such regions are instead entirely et al. 2007), but also provide essential vitamins, reliant on managed honey bees for pollination nutrients and fiber for a healthy diet and provide services. If trends towards increased diet diversity (Gallai et al. 2009; Kremen et al. agricultural intensification continue elsewhere 2007). The nutritional consequences of total (e.g. as in Brazil, Morton et al. 2006), then pollinator loss for human health have yet to be pollination services from wild pollinators are quantified; however food recommendations for highly likely to decline in other regions minimal daily portions of fruits and vegetables (Ricketts et al. 2008). At the same time, global are well‐known and already often not met in food production is shifting increasingly towards diets of both developed and underdeveloped production of pollinator‐dependent foods countries. (Aizen et al. 2008), increasing our need for managed and wild pollinators yet further. REFERENCES Global warming, which could cause mis‐ matches between pollinators and the plants Aizen, M. A., Garibaldi, L. A., Cunningham, S. A., and they feed upon, may exacerbate pollinator Klein, A. M. (2008). Long‐term global trends in crop decline (Memmott et al. 2007). For these yield and production reveal no current pollination continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 77. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL Box 3.5 (Continued) shortage but increasing pollinator dependency. Current Memmott, J., Craze, P. G., Waser, N. M., and Price, Biology, 18, 1572–1575. M. V. (2007). Global warming and the disruption Biesmeijer, J. C., Roberts, S. P. M., Reemer, M., et al. (2006). of plant‐pollinator interactions. Ecology Letters, Parallel declines in pollinators and insect‐pollinated plants in 10, 710–717. Britain and the Netherlands. Science, 313, 351–354. Morton, D. C., DeFries, R. S., Shimabukuro, Y. E., et al., Cox‐Foster, D. L., Conlan, S., Holmes, E. C., et al. (2007). (2006). Cropland expansion changes deforestation dy- A metagenomic survey of microbes in honey bee colony namics in the southern Brazilian Amazon. Proceedings collapse disorder. Science, 318, 283–287. of the National Academy of Sciences of the United Gallai, N., Salles, J.‐M., Settele, J., and Vaissière, B. E. States of America, 103, 14637–14641. (2009). Economic valuation of the vulnerability of world NRC (National Research Council of the National agriculture confronted with pollinator decline. Ecologi- Academies) (2006). Status of Pollinators in North cal Economics, 68, 810–821. America. National Academy Press, Goulson, D., Lye, G. C., and Darvill, B. (2008). Decline and Washington, DC. conservation of bumblebees. Annual Review of Ento- Ricketts, T. H., Regetz, J., Steffan‐Dewenter, I., et al. mology, 53, 191–208. (2008) Landscape effects on crop pollination services: Klein, A. M., Vaissièrie, B., Cane, J. H., et al. (2007). are there general patterns? Ecology Letters, Importance of crop pollinators in changing landscapes 11, 499–515. for world crops. Proceedings of the Royal Society of Southwick, E. E. and Southwick, L. Jr. (1992). Estimating the London B, 274, 303–313. economic value of honey bees (Hymenoptera: Apidae) as Kremen, C., Williams, N. M., and Thorp, R. W. (2002). Crop agricultural pollinators in the United States. Journal of pollination from native bees at risk from agricultural inten- Economic Entomology, 85, 621–633. sification. Proceedings of the National Academy of Sciences Stokstad, E. (2007). The case of the empty hives. Science, of the United States of America, 99, 16812–16816. 316, 970–972. Kremen, C., Williams, N. M., Aizen, M. A., et al. (2007). Sumner, D. A. and Boriss, H. (2006). Bee‐conomics and the Pollination and other ecosystem services produced by leap in pollination fees. Giannini Foundation of Agricul- mobile organisms: a conceptual framework for the tural Economics Update, 9, 9–11. effects of land‐use change. Ecology Letters, 10, 299314. Taki, H. and Kevan, P. G. (2007). Does habitat loss Larsen, T. H., Williams, N. M., and Kremen, C. (2005). Extinc- affect the communities of plants and insects equally tion order and altered community structure rapidly disrupt in plant‐pollinator interactions? Preliminary findings. ecosystem functioning. Ecology Letters, 8, 538–547. Biodiversity and Conservation, 16, 3147–3161.their ability to self-pollinate and have become crops every year (Pimentel et al. 1989). In the UScompletely dependent on endemic pollinators alone, despite the US$25 billion spent on pesticides(Cox and Elmqvist 2000). Pollination limitation annually (Naylor and Ehrlich 1997), pests destroydue to the reduced species richness of pollinators 37% of the potential crop yield (Pimentel et al.on islands like New Zealand and Madagascar (Far- 1997). However, many pests have evolved resis-wig et al. 2004) can significantly reduce fruit sets tance to the millions of tons of synthetic pesticideand probably decrease the reproductive success of sprayed each year (Pimentel and Lehman 1993),dioecious plant species. largely due to insects’ short generation times and Predators are important trophic process links their experience with millions of years of coevolu-and can control the populations of pest species. tion with plant toxins (Ehrlich and Raven 1964).For millennia, agricultural pests have been compet- Consequently, these chemicals poison the environ-ing with people for the food and fiber plants that ment (Carson 1962), lead to thousands of wildlifefeed and clothe humanity. Pests, particularly her- fatalities every year, and by killing pests’ naturalbivorous insects, consume 25–50% of humanity’s enemies faster than the pests themselves, often lead© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 78. 1 ECOSYSTEM FUNCTIONS AND SERVICES 63to the emergence of new pest populations (Naylor (Prakash et al. 2003) and where vultures contrib-and Ehrlich 1997). As a result, the value of natural ute to human and ecosystem health by getting ridpest control has been increasingly recognized of refuse (Pomeroy 1975), feces (Negro et al. 2002),worldwide, some major successes have been and dead animals (Prakash et al. 2003).achieved, and natural controls now form a core Mobile links also transport nutrients from onecomponent of “integrated pest management” habitat to another. Some important examples are(IPM) that aims to restore the natural pest-predator geese transporting terrestrial nutrients to wetlandsbalance in agricultural ecosystems (Naylor and (Post et al. 1998) and seabirds transferring marineEhrlich 1997). productivity to terrestrial ecosystems, especially in Species that provide natural pest control range coastal areas and unproductive island systemsfrom bacteria and viruses to invertebrate and (Sanchez-pinero and Polis 2000). Seabird drop-vertebrate predators feeding on insect and rodent pings (guano) are enriched in important plant nu-pests (Polis et al. 2000; Perfecto et al. 2004; Seker- trients such as calcium, magnesium, nitrogen,cioglu 2006b). For example, a review by Holmes phosphorous, and potassium (Gillham 1956). Mur-(1990) showed that reductions in moth and but- phy (1981) estimated that seabirds around theterfly populations due to temperate forest birds world transfer 104 to 105 tons of phosphorouswas mostly between 40–70% at low insect densi- from sea to land every year. Guano also providesties, 20–60% at intermediate densities, and 0–10% an important source of fertilizer and income toat high densities. Although birds are not usually many people living near seabird colonies.thought of as important control agents, avian Scavengers and seabirds provide good exam-control of insect herbivores and consequent re- ples of how the population declines of ecosystemductions in plant damage can have important service providers lead to reductions in their ser-economic value (Mols and Visser 2002). Take- vices (Hughes et al. 1997). Scavenging and fish-kawa and Garton (1984) calculated avian control eating birds comprise the most threatened avianof western spruce budworm in northern Wa- functional groups, with about 40% and 33%, re-shington State to be worth at least US$1820/ spectively, of these species being threatened orkm2/year. To make Beijing greener for the 2008 near threatened with extinction (SekerciogluOlympics without using chemicals, entomolo- et al. 2004). The large declines in the populationsgists reared four billion parasitic wasps to get of many scavenging and fish-eating species meanrid of the defoliating moths in less than three that even if none of these species go extinct, theirmonths (Rayner 2008). Collectively, natural ene- services are declining substantially. Seabird lossesmies of crop pests may save humanity at least US can trigger trophic cascades and ecosystem shifts$54 billion per year, not to mention the critical (Croll et al. 2005). Vulture declines can lead to theimportance of natural controls for food security emergence of public health problems. In India,and human survival (Naylor and Ehrlich 1997). Gyps vulture populations declined as much asPromoting natural predators and preserving their 99% in the 1990s (Prakash et al. 2003). Vulturesnative habitat patches like hedgerows and forests compete with feral dogs, which often carry rabies.may increase crop yields, improve food security, As the vultures declined between 1992 and 2001,and lead to a healthier environment. the numbers of feral dogs increased 20-fold at a Often underappreciated are the scavenging garbage dump in India (Prakash et al. 2003). Mostand nutrient deposition services of mobile links. of world’s rabies deaths take place in India (WorldScavengers like vultures rapidly get rid of rotting Health Organization 1998) and feral dogs replacingcarcasses, recycle nutrients, and lead other ani- vultures is likely to aggravate this problem.mals to carcasses (Sekercioglu 2006a). Besides Mobile links, however, can be double-edgedtheir ecological significance, vultures are particu- swords and can harm ecosystems and human po-larly important in many tropical developing pulations, particularly in concert with humancountries where sanitary waste and carcass dis- related poor land-use practices, climate change,posal programs may be limited or non-existent and introduced species. Invasive plants can spread© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 79. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLvia native and introduced seed dispersers (Larosa traditional, rural communities to urban areas, andet al. 1985; Cordeiro et al. 2004). Land use change disappearing cultures and languages mean that thecan increase the numbers of mobile links that dam- priceless ethnobotanical knowledge of many cul-age distant areas, such as when geese overload tures is rapidly disappearing in parallel with thewetlands with excessive nutrients (Post et al. impending extinctions of many medicinal plants1998). Climate change can lead to asynchronies in due to habitat loss and overharvesting (Millenni-insect emergence and their predators timing of um Ecosystem Assessment 2005a). Some of thebreeding (Both et al. 2006), and in flowering and rainforest areas that are being deforested fastest,their pollinators lifecycles (Harrington et al. 1999) like the island of Borneo, harbor plant species that(Chapter 8). produce active anti-HIV (Human Immunodefi- Mobile links are often critical to ecosystem func- ciency Virus) agents (Chung 1996; Jassim andtioning as sources of “external memory” that pro- Naji 2003). Doubtlessly, thousands more usefulmote the resilience of ecosystems (Scheffer et al. and vital plant compounds await discovery in the2001). More attention needs to be paid to mobile forests of the world, particularly in the biodiverselinks in ecosystem management and biodiversity tropics (Laurance 1999; Sodhi et al. 2007). However,conservation (Lundberg and Moberg 2003). This is without an effective strategy that integrates com-especially the case for migrating species that face munity-based habitat conservation, rewardingcountless challenges during their annual migra- of local ethnobotanical knowledge, and scientifictions that sometimes cover more than 20 000 kilo- research on these compounds, many species, themeters (Wilcove 2008). Some of the characteristics local knowledge of them, and the priceless curesthat make mobile links important for ecosystems, they offer will disappear before scientists discoversuch as high mobility and specialized diets, also them.make them more vulnerable to human impact. As with many of nature’s services, there is a flipProtecting pollinators, seed dispersers, predators, side to the medicinal benefits of biodiversity,scavengers, nutrient depositors, and other mobile namely, emerging diseases ( Jones et al. 2008).links must be a top conservation priority to prevent The planet’s organisms also include countlesscollapses in ecosystem services provided by these diseases, many of which are making the transi-vital organisms (Boxes 3.1–3.5). tion to humans as people increasingly invade the habitats of the hosts of these diseases and con- sume the hosts themselves. Three quarters of human diseases are thought to have their origins3.6 Nature’s Cures versus Emerging in domestic or wild animals and new diseases areDiseases emerging as humans increase their presence inWhile many people know about how plants pre- formerly wilderness areas (Daily and Ehrlichvent erosion, protect water supplies, and “clean the 1996; Foley et al. 2005). Some of the deadliestair”, how bees pollinate plants or how owls reduce diseases, such as monkeypox, malaria, HIV androdent activity, many lesser-known organisms not Ebola, are thought to have initially crossed fromonly have crucial ecological roles, but also produce central African primates to the people whounique chemicals and pharmaceuticals that can hunted, butchered, and consumed them (Hahnliterally save people’s lives. Thousands of plant et al. 2000; Wolfe et al. 2005; Rich et al. 2009).species are used medically by traditional, indige- Some diseases emerge in ways that show thenous communities worldwide. These peoples’ eth- difficulty of predicting the consequences of dis-nobotanical knowledge has led to the patenting, by turbing ecosystems. The extensive smoke frompharmaceutical companies, of more than a quarter the massive 1997–1998 forest fires in Southeastof all medicines (Posey 1999), although the indige- Asia is thought to have led to the fruiting failurenous communities rarely benefit from these pa- of many forest trees, forcing frugivorous bats totents (Mgbeoji 2006). Furthermore, the eroding of switch to fruit trees in pig farms. The bats, whichtraditions worldwide, increasing emigration from host the Nipah virus, likely passed it to the pigs,© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 80. 1 ECOSYSTEM FUNCTIONS AND SERVICES 65from which the virus made the jump to people Collectively, the conditions leading to and result-(Chivian 2002). Another classic example from ing from tropical deforestation, combined withSoutheast Asia is the Severe Acute Respiratory climate change, human migration, agriculturalSyndrome (SARS). So far having killed 774 peo- intensification, and animal trafficking create theple, the SARS coronavirus has been recently dis- perfect storm for the emergence of new diseasescovered in wild animals like the masked palm as well as the resurgence of old ones. In the face ofcivet (Paguma larvata) and raccoon dog (Nyctereu- rapid global change, ecologically intact and rela-teus procyonoides) that are frequently consumed tively stable communities may be our best weap-by people in the region (Guan et al. 2003). SARS- on against the emergence of new coronaviruses have been discovered in bats(Li et al. 2005) and the virus was probably passedto civets and other animals as they ate fruits 3.7 Valuing Ecosystem Servicespartially eaten and dropped by those bats (JamieH. Jones, personal communication). It is probable Ecosystems and their constituent species providethat SARS made the final jump to people through an endless stream of products, functions, and ser-such animals bought for food in wildlife markets. vices that keep our world running and make our The recent emergence of the deadly avian influ- existence possible. To many, even the thought ofenza strain H5N1 provides another good example. putting a price tag on services like photosynthesis,Even though there are known to be at least 144 purification of water, and pollination of food cropsstrains of avian flu, only a few strains kill people. may seem like hubris, as these are truly pricelessHowever, some of the deadliest pandemics have services without which not only humans, but mostbeen among these strains, including H1N1, H2N, of life would perish. A distinguished economist putand H3N2 (Cox and Subbarao 2000). H5N1, the it best in response to a seminar at the USA Federalcause of the recent bird flu panic, has a 50% fatality Trade Commission, where the speaker down-rate and may cause another human pandemic. played the impact of global warming by sayingAt low host densities, viruses that become too agriculture and forestry “accounted for only threedeadly, fail to spread. It is likely that raising do- percent of the US gross national product”. The econ-mestic birds in increasingly higher densities led to omist’s response was: “What does this genius thinkthe evolution of higher virulence in H5N1, as it we’re going to eat?” (Naylor and Ehrlich 1997).became easier for the virus to jump to another Nevertheless, in our financially-driven world,host before it killed its original host. There is also we need to quantify the trade-offs involved ina possibility that increased invasion of wilderness land use scenarios that maximize biodiversity con-areas by people led to the jump of H5N1 from wild servation and ecosystem services versus scenariosbirds to domestic birds, but that is yet to be proven. that maximize profit from a single commodity. Malaria, recently shown to have jumped from Without such assessments, special interests repre-chimpanzees to humans (Rich et al. 2009), is per- senting single objectives dominate the debate andhaps the best example of a resurging disease that sideline the integration of ecosystem services intoincreases as a result of tropical deforestation the decision-making process (Nelson et al. 2009).(Singer and Castro 2001; Foley et al. 2005; Ya- Valuing ecosystem services is not an end in itself,suoka and Levins 2007). Pearson (2003) calculat- but is the first step towards integrating these ser-ed that every 1% increase in deforestation in the vices into public decision-making and ensuring theAmazon leads to an 8% increase in the population continuity of ecosystems that provide the servicesof the malaria vector mosquito (Anopheles dar- (Goulder and Kennedy 1997; National Researchlingi). In addition, some immigrants colonizing Council 2005; Daily et al. 2009). Historically, eco-deforested areas brought new sources of malaria system services have been mostly thought of as(Moran 1988) whereas other immigrants come free public goods, an approach which has too fre-from malaria-free areas and thus become ideal quently led to the “tragedy of the commons”hosts with no immunity (Aiken and Leigh 1992). where vital ecosystem goods like clean water© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 81. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLhave been degraded and consumed to extinction versity they harbor, and the services they collec-(Daily 1997). Too often, ecosystem services have tively provide are truly priceless, market-basedbeen valued, if at all, based on “marginal utility” and other quantitative approaches for valuing(Brauman and Daily 2008). When the service (like ecosystem services will raise the profile of nat-clean water) is abundant, the marginal utility of one ure’s services in the public consciousness, inte-additional unit can be as low as zero. However, as grate these services into decision-making, andthe service becomes more scarce, the marginal utility help ensure the continuity of ecosystem contribu-of each additional unit becomes increasingly valu- tions to the healthy functioning of our planet andable (Goulder and Kennedy 1997). Using the mar- its residents.ginal value for a service when it is abundantdrastically underestimates the value of the serviceas it becomes scarcer. As Benjamin Franklin wryly Summaryobserved, “When the well’s dry, we know the worthof water.” As the societal importance of ecosystem services · Ecosystem services are the set of ecosystem func- tions that are useful to humans.becomes increasingly appreciated, there has beena growing realization that successful application · These services make the planet inhabitable by supplying and purifying the air we breathe and theof this concept requires a skilful combination of water we drink.biological, physical, and social sciences, as well asthe creation of new programs and institutions. The · Water, carbon, nitrogen, phosphorus, and sulfur are the major global biogeochemical cycles. Disrup-scientific community needs to help develop the tions of these cycles can lead to floods, droughts,necessary quantitative tools to calculate the value climate change, pollution, acid rain, and many otherof ecosystem services and to present them to the environmental problems.decision makers (Daily et al. 2009). A promisingexample is the InVEST (Integrated Valuation of · Soils provide critical ecosystem services, especial- ly for sustaining ecosystems and growing foodEcosystem Services and Tradeoffs) system crops, but soil erosion and degradation are serious(Daily et al. 2009; Nelson 2009) developed by the problems worldwide.Natural Capital Project (;see Box 15.3). However, good tools are valuable · Higher biodiversity usually increases ecosystem efficiency and productivity, stabilizes overall eco-only if they are used. A more difficult goal is system functioning, and makes ecosystems moreconvincing the private and public sectors to resistant to perturbations.incorporate ecosystem services into their deci-sion-making processes (Daily et al. 2009). Never- · Mobile link animal species provide critical eco- system functions and increase ecosystem resiliencetheless, with the socio-economic impacts and by connecting habitats and ecosystems throughhuman costs of environmental catastrophes, their movements. Their services include pollination,such as Hurricane Katrina, getting bigger and seed dispersal, nutrient deposition, pest control, andmore visible, and with climate change and related scavenging.carbon sequestration schemes having reacheda prominent place in the public consciousness, · Thousands of species that are the components of ecosystems harbor unique chemicals and pharma-the value of these services and the necessity of ceuticals that can save people’s lives, but traditionalmaintaining them has become increasingly main- knowledge of medicinal plants is disappearing andstream. many potentially valuable species are threatened Recent market-based approaches such as pay- with extinction.ments for Costa Rican ecosystem services, wet-land mitigation banks, and the Chicago Climate · Increasing habitat loss, climate change, settle- ment of wild areas, and wildlife consumption facili-Exchange have proven useful in the valuation of tate the transition of diseases of animals to humans,ecosystem services (Brauman and Daily 2008). and other ecosystem alterations are increasing theEven though the planet’s ecosystems, the biodi- prevalence of other diseases.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 82. 1 ECOSYSTEM FUNCTIONS AND SERVICES 67· Valuation of ecosystem services and tradeoffshelps integrate these services into public decision- Bawa, K. S. (1990). Plant-pollinator interactions in Tropical Rain-Forests. Annual Review of Ecology and Systematics,making and can ensure the continuity of ecosystems 21, 399–422.that provide the services. Berhe, A. A., Harte, J., Harden, J. W., and Torn, M. S. (2007). The significance of the erosion-induced terrestrial carbon sink. BioScience, 57, 337–46. Berlow, E. L. (1999). Strong effects of weak interactions inRelevant websites ecological communities. Nature, 398, 330–34. Bolin, B. and Cook, R. B., eds (1983). The major biogeochemi-· Millennium Ecosystem Assessment: cal cycles and their interactions. Wiley, New York.· Intergovernmental Panel on Climate Change: http:// Bolker, B. M., Pacala, S. W., Bazzaz, F. A., Canham, C. D., and Levin, S. A. (1995). Species diversity and ecosystem re- sponse to carbon dioxide fertilization: conclusions from a· Ecosystem Marketplace: http://www.ecosystemmar- temperate forest model. Global Change Biology, 1, 373–381. Both, C., Bouwhuis, S., Lessells, C. M., and Visser, M. E.· United States Department of Agriculture, Forest Service Website on Ecosystem Services: (2006). Climate change and population declines in a long-distance migratory bird. Nature, 441, 81–83. ecosystemservices/ Bradshaw, C. J. A., Sodhi, N. S., Peh, K. S.-H., and Brook, B.· Ecosystem Services Project: http://www.ecosystemser- W. (2007). Global evidence that deforestation amplifies flood risk and severity in the developing world. Global· Natural Capital Project: http://www.naturalcapital- Change Biology, 13, 2379–2395. Brauman, K. A., and G. C. Daily. (2008). Ecosystem· Carbon Trading: services. In S. E. Jorgensen and B. D. Fath, ed. Human Ecology, pp. 1148–1154. Elsevier, Oxford, UK. Brauman, K. A., Daily, G. C., Duarte, T. K., and Mooney, H. A. (2007). The nature and value of ecosys-Acknowledgements tem services: an overview highlighting hydrologic services. Annual Review of Environment and Resources,I am grateful to Karim Al-Khafaji, Berry Brosi, Paul R. 32, 67–98.Ehrlich, Jamie H. Jones, Stephen Schneider, Navjot Sodhi, Bruijnzeel, L. A. (2004). Hydrological functions of tropicalTanya Williams, and especially Kate Brauman for their forests: not seeing the soil for the trees? Agriculturevaluable comments. I thank the Christensen Fund for Ecosystems and Environment, 104, 185–228.their support of my conservation and ecology work. Bruno, J. F. and Selig, E. R. (2007). Regional decline of coral cover in the Indo-Pacific: timing, extent, and subregional comparisons. PLoS One, 2, e711. Burd, M. (1994). Bateman’s principle and plant reproduc-REFERENCES tion: the role of pollen limitation in fruit and seed set. Botanical Review, 60, 81–109.Aiken, S. R. and Leigh, C. H. (1992). Vanishing rain forests. Butler, R. (2008). Despite financial chaos, donors pledge Clarendon Press, Oxford, UK. $100M for rainforest conservation. http://news.mongabay.Alexander, S. E., Schneider, S. H., and Lagerquist, K. com/2008/1023-fcpf.html. (1997). The interaction of climate and life. In G. C. Cain, M. L., Milligan, B. G., and Strand, A. E. (2000). Long- Daily, ed. Nature’s Services, pp. 71–92. Island Press, distance seed dispersal in plant populations. American Washington DC. Journal of Botany, 87, 1217–1227.Anderson, W. B. and Polis, G. A. (1999). Nutrient fluxes Calder, I. R. and Aylward, B. (2006). Forest and floods: from water to land: seabirds affect plant nutrient status Moving to an evidence-based approach to watershed on Gulf of California islands. Oecologia, 118, 324–32. and integrated flood management. Water International,Avinash, N. (2008). Soil no bar: Gujarat farmers going hi- 31, 87–99. tech. The Economic Times, 24 July. Canada’s Office of Urban Agriculture (2008). Urban agricul-Ba, L. K. (1977). Bio-economics of trees in native Malayan ture notes. City Farmer, Vancouver, Canada. forest. Department of Botany, University of Malaya, Carson, R. (1962). Silent Spring. Houghton Mifflin, Boston, Kuala Lumpur. MA.© Oxford University Press 2010. All rights reserved. For permissions please email:
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  • 87. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL erosion to near natural benchmark levels. Geology, 35, of zoonoses emergence. Emerging Infectious Diseases, 11, 303–06. 1822–1827.Vitousek, P. M. and Hooper, D. U. (1993). Biological diver- World Health Organization. (1998). World Survey for sity and terrestrial ecosystem productivity. In D. E. Rabies No. 34. World Health Organization, Geneva, Schulze, and H. A. Mooney, eds Biodiversity and ecosys- Switzerland. tem function, pp. 3–14. Springer-Verlag, Berlin, Germany. Worm, B., Barbier, E. B., Beaumont, N., et al. (2006). Im-Vitousek, P. M., Aber, J. D., Howard, R. W., et al. (1997). pacts of biodiversity loss on ocean ecosystem services. Human alteration of the global nitrogen cycle: sources Science, 314, 787–790. and consequences. Ecological Applications, 7, 737–750. Wright, S. J. (2005). Tropical forests in a changing environ-Walker, B., Kinzig, A., and Langridge, J. (1999). Plant attri- ment. Trends in Ecology and Evolution, 20, 553–560. bute diversity, resilience, and ecosystem function: the Wunderle, J. M. (1997). The role of animal seed dispersal nature and significance of dominant and minor species. in accelerating native forest regeneration on de- Ecosystems, 2, 95–113. graded tropical lands. Forest Ecology and Management,Wilcove, D. S. (2008). No way home: the decline of the 99, 223–235. world’s great animal migrations. Island Press, Washing- Yasuoka, J., and R. Levins. (2007). Impact of deforestation ton, DC. and agricultural development on Anopheline ecologyWolfe, N. D., Daszak, P., Kilpatrick, A. M., and Burke, D. S. and malaria epidemiology. American Journal of Tropical (2005). Bushmeat hunting deforestation, and prediction Medicine and Hygiene, 76, 450–460.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 88. 1 CHAPTER 4 Habitat destruction: death by a thousand cuts William F. LauranceHumankind has dramatically transformed much 4.1 Habitat loss and fragmentationof the Earth’s surface and its natural ecosystems. Habitat destruction occurs when a natural habitat,This process is not new—it has been ongoing for such as a forest or wetland, is altered so dramati-millennia—but it has accelerated sharply over the cally that it no longer supports the species it origi-last two centuries, and especially in the last sev- nally sustained. Plant and animal populations areeral decades. destroyed or displaced, leading to a loss of biodi- Today, the loss and degradation of natural ha- versity (see Chapter 10). Habitat destruction isbitats can be likened to a war of attrition. Many considered the most important driver of speciesnatural ecosystems are being progressively razed, extinction worldwide (Pimm and Raven 2000).bulldozed, and felled by axes or chainsaws, until Few habitats are destroyed entirely. Very often,only small scraps of their original extent survive. habitats are reduced in extent and simultaneouslyForests have been hit especially hard: the global fragmented, leaving small pieces of original habi-area of forests has been reduced by roughly half tat persisting like islands in a sea of degradedover the past three centuries. Twenty-five nations land. In concert with habitat loss, habitat frag-have lost virtually all of their forest cover, and mentation is a grave threat to species survivalanother 29 more than nine-tenths of their forest (Laurance et al. 2002; Sekercioglu et al. 2002;(MEA 2005). Tropical forests are disappearing Chapter 5).at up to 130 000 km2 a year (Figure 4.1)—roughly Globally, agriculture is the biggest cause of hab-50 football fields a minute. Other ecosystems itat destruction (Figure 4.2). Other human activ-are less imperiled, and a few are even recover- ities, such as mining, clear-cut logging, trawling,ing somewhat following past centuries of overex- and urban sprawl, also destroy or severely degradeploitation. habitats. In developing nations, where most habi- Here I provide an overview of contemporary tat loss is now occurring, the drivers of environ-habitat loss. Other chapters in this book descr- mental change have shifted fundamentally inibe the many additional ways that ecosystems recent decades. Instead of being caused mostly byare being threatened—by overhunting (Chapter small-scale farmers and rural residents, habitat6), habitat fragmentation (Chapter 5), and climate loss, especially in the tropics, is now substantiallychange (Chapter 8), among other causes—but driven by globalization promoting intensive agri-my emphasis here is on habitat destruction culture and other industrial activities (see Box 4.1).per se. I evaluate patterns of habitat destructiongeographically and draw comparisons amongdifferent biomes and ecosystems. I then consider 4.2 Geography of habitat losssome of the ultimate and proximate factors thatdrive habitat loss, and how they are changing Some regions of the Earth are far more affected bytoday. habitat destruction than others. Among the most 73© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 89. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLFigure 4.1 The aftermath of slash‐and‐burn farming in central Amazonia. Photograph by W. F. Laurance.imperiled are the so-called “biodiversity hotspots”, and degraded, are examples of biodiversity hot-which contain high species diversity, many locally spots. Despite encompassing just a small fractionendemic species (those whose entire geographic (2%) of the Earth’s land surface, hotspots mayrange is confined to a small area), and which have sustain over half of the world’s terrestrial specieslost at least 70% of their native vegetation (Myers (Myers et al. 2000).et al. 2000). Many hotspots are in the tropics. The Many islands have also suffered heavy habitatAtlantic forests of Brazil and rainforests of West loss. For instance, most of the original naturalAfrica, both of which have been severely reduced habitat has already been lost in Japan, NewFigure 4.2 Extent of land area cultivated globally by the year 2000. Reprinted from MEA (2005).© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 90. 1 HABITAT DESTRUCTION: DEATH BY A THOUSAND CUTS 75 Box 4.1 The changing drivers of tropical deforestation William F. Laurance Tropical forests are being lost today at an alarming pace. However, the fundamental (b) drivers of tropical forest destruction have changed in recent years (Rudel 2005; Butler and Laurance 2008). Prior to the late 1980s, deforestation was generally caused by rapid human population growth in developing nations, in concert with government policies for rural development. These included agricultural loans, tax incentives, and road construction. Such initiatives, especially evident in countries such as Brazil and Indonesia, promoted large influxes of colonists into frontier areas and often caused dramatic forest loss. Box 4.1 Figure Changing drivers of deforestation: Small‐scale More recently, however, the impacts of rural cultivators (a) versus industrial road construction (b) in Gabon, peoples on tropical forests seem to be central Africa. Photograph by W. F. Laurance. stabilizing (see Box 4.1 Figure). Although At the same time, globalized financial many tropical nations still have considerable markets and a worldwide commodity boom are population growth, strong urbanization creating a highly attractive environment for trends (except in Sub‐Saharan Africa) mean the private sector. Under these conditions, that rural populations are growing more large‐scale agriculture—crops, livestock, and slowly, and are even declining in some tree plantations—by corporations and wealthy areas. The popularity of large‐scale frontier‐ landowners is increasingly emerging as the colonization programs has also waned. biggest direct cause of tropical deforestation If such trends continue, they could begin (Butler and Laurance 2008). Surging demand to alleviate some pressures on forests for grains and edible oils, driven by the global from small‐scale farming, hunting, and thirst for biofuels and rising standards of living fuel‐wood gathering (Wright and Muller‐ in developing countries, is also spurring this landau 2006). trend. In Brazilian Amazonia, for instance, large‐scale ranching has exploded in recent (a) years, with the number of cattle more than tripling (from 22 to 74 million head) since 1990 (Smeraldi and May 2008), while industrial soy farming has also grown dramatically. Other industrial activities, especially logging, mining, and petroleum development, are also playing a critical but indirect role in forest destruction (Asner et al. 2006; Finer et al. 2008). These provide a key economic impetus for forest road‐building (see Box 4.1 Figure), which in turn allows influxes of colonists, hunters, and miners into frontier areas, often leading to rapid forest disruption and cycles of land speculation. continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 91. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL Box 4.1 (Continued) REFERENCES threats to wilderness, biodiversity, and indigenous peoples. PLoS One, doi:10.1371/journal.pone.0002932. Asner, G. P., Broadbent, E., Oliveira, P., Keller, M., Knapp, Rudel, T. K. (2005). Changing agents of deforestation: D., and Silva, J. (2006). Condition and fate of logged from state‐initiated to enterprise driven processes, forests in the Amazon. Proceedings of the National 1970–2000. Land Use Policy, 24, 35–41. Academy of Sciences of the United States of America. Smeraldi, R. and May, P. H. (2008). The cattle realm: 103, 12947–12950. a new phase in the livestock colonization of Butler, R. A. and Laurance, W. F. (2008). New strategies Brazilian Amazonia. Amigos da Terra, Amazônia for conserving tropical forests. Trends in Ecology and Brasileira, São Paulo, Brazil. Evolution, 23, 469–72. Wright, S. J. and Muller‐Landau, H. C. (2006). The Finer, M., Jenkins, C., Pimm, S., Kean, B., and Rossi, C. future of tropical forest species. Biotropica, 38, (2008). Oil and gas projects in the western Amazon: 287–301.Zealand, Madagascar, the Philippines, and Java palm or rubber plantations (MacKinnon 2006;(WRI 2003). Other islands, such as Borneo, Suma- Laurance 2007; Koh and Wilcove 2008; see Boxtra, and New Guinea, still retain some original 13.3). Older agricultural frontiers, such as those inhabitat but are losing it at alarming rates (Curran Europe, eastern China, the Indian Subcontinent,et al. 2004; MacKinnon 2006). and eastern and midwestern North America, Most areas of high human population density often have very little native vegetation remaininghave suffered heavy habitat destruction. Such (Figure 4.2).areas include much of Europe, eastern NorthAmerica, South and Southeast Asia, the MiddleEast, West Africa, Central America, and the Ca- 4.3 Loss of biomes and ecosystemsribbean region, among others. Most of the biodi- 4.3.1 Tropical and subtropical forestsversity hotspots occur in areas with high humandensity (Figure 4.3) and many still have rapid A second way to assess habitat loss is by contrast-population growth (Cincotta et al. 2000). Human ing major biomes or ecosystem types (Figure 4.4).populations are often densest in coastal areas, Today, tropical rainforests (also termed tropicalmany of which have experienced considerable moist and humid forests) are receiving the greatestlosses of both terrestrial habitats and nearby attention, because they are being destroyedcoral reefs. Among others, coastal zones in Asia, so rapidly and because they are the most biologi-northern South America, the Caribbean, Europe, cally diverse of all terrestrial biomes. Of the rough-and eastern North America have all suffered se- ly 16 million km2 of tropical rainforest thatvere habitat loss (MEA 2005). originally existed worldwide, less than 9 million Finally, habitat destruction can occur swiftly in km2 remains today (Whitmore 1997; MEA 2005).areas with limited human densities but rapidly The current rate of rainforest loss is debated, withexpanding agriculture. Large expanses of the different estimates ranging from around 60 000Amazon, for example, are currently being cleared km2 (Achard et al. 2002) to 130 000 km2 per yearfor large-scale cattle ranching and industrial (FAO 2000). Regardless of which estimate one ad-soy farming, despite having low population den- heres to, rates of rainforest loss are alarmingly high.sities (Laurance et al. 2001). Likewise, in some Rates of rainforest destruction vary consider-relatively sparsely populated areas of Southeast ably among geographic regions. Of the world’sAsia, such as Borneo, Sumatra, and New Guinea, three major tropical regions, Southeast Asian for-forests are being rapidly felled to establish oil- ests are disappearing most rapidly in relative© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 92. 1 HABITAT DESTRUCTION: DEATH BY A THOUSAND CUTS 77Figure 4.3 Human population density in 1995 within 25 recognized biodiversity hotspots (numbered 1‐25) and three major tropical wildernesses(labeled A‐C). Reprinted from Cincotta et al. 2000 © Nature Publishing Group.terms (Figure 4.5), while the African and New gion as a whole is buffered by the vastness of theWorld tropics have somewhat lower rates of per- Amazon. Likewise, in tropical Africa, forest loss iscent-annual forest loss (Sodhi et al. 2004). Such severe in West Africa, montane areas of Eastaverages, however, disguise important smaller- Africa, and Madagascar, but substantial forestscale variation. In the New World tropics, for ex- still survives in the Congo Basin (Laurance 1999).ample, the Caribbean, MesoAmerican, and An- Other tropical and subtropical biomes havedean regions are all suffering severe rainforest suffered even more heavily than rainforestsloss, but the relative deforestation rate for the re- (Figure 4.4). Tropical dry forests (also known as Fraction of potential area converted (%) –10 0 10 20 30 40 50 60 70 80 90 100 Mediterranean forests, woodlands, and scrub Temperate forest steppe and woodland Temperate broadleaf and mixed forest Tropical and sub-tropical dry broadleaf forests Flooded grasslands and savannas Tropical and sub-tropical grasslands, savannas, and shrublands Tropical and sub-tropical coniferous forests Deserts Montane grasslands and shrublands Tropical and sub-tropical moist broadleaf forests Temperate coniferous forests Boreal forests Loss by 1950 Tundra Loss between 1950 and 1990 Projected loss by 2050Figure 4.4 Estimated losses of major terrestrial biomes prior to 1950 and from 1950 to 1990, with projected losses up to 2050. Reprinted from MEA (2005).© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 93. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLFigure 4.5 Tropical rainforests in Southeast Asia are severely imperiled, as illustrated by this timber operation in Indonesian Borneo. Photograph byW. F. Laurance.monsoonal or deciduous forests) have been se- ests and woodlands, temperate broadleaf andverely reduced, in part because they are easier mixed forests, and temperate forest-steppe andto clear and burn than rainforests. For instance, woodlands have all suffered very heavy lossesalong Central America’s Pacific coast, much less (Figure 4.4), given the long history of humanthan 1% of the original dry forest survives. Losses settlement in many temperate regions. By 1990of dry forest have been nearly as severe in Mada- more than two-thirds of Mediterranean forestsgascar and parts of Southeast Asia (Laurance and woodlands were lost, usually because they1999; Mayaux et al. 2005). were converted to agriculture (MEA 2005). In the Mangrove forests, salt-tolerant ecosystems that eastern USA and Europe (excluding Russia), old-grow in tropical and subtropical intertidal zones, growth broadleaf forests (100 years old) havehave also been seriously reduced. Based on nearly disappeared (Matthews et al. 2000), al-countries for which data exist, more than a third though forest cover is now regenerating inof all mangroves were lost in the last few decades many areas as former agricultural lands are aban-of the 20th century (MEA 2005). From 1990 to doned and their formerly rural, farming-based2000, over 1% of all mangrove forests were lost populations become increasingly urbanized.annually, with rates of loss especially high in In the cool temperate zone, coniferous forestsSoutheast Asia (Mayaux et al. 2005). Such losses have been less severely reduced than broadleafare alarming given the high primary productivity and mixed forests, with only about a fifth beingof mangroves, their key role as spawning and lost by 1990 (Figure 4.4). However, vast expansesrearing areas for economically important fish of coniferous forest in northwestern North Amer-and shrimp species, and their importance for ica, northern Europe, and southern Siberia aresheltering coastal areas from destructive storms being clear-felled for timber or pulp production.and tsunamis (Danielsen et al. 2005). As a result, these semi-natural forests are con- verted from old-growth to timber-production for- ests, which have a much-simplified stand4.3.2 Temperate forests and woodlands structure and species composition. Large expansesSome ecosystems have suffered even worse de- of coniferous forest are also burned each yearstruction than tropical forests. Mediterranean for- (Matthews et al. 2000).© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 94. 1 HABITAT DESTRUCTION: DEATH BY A THOUSAND CUTS 79Figure 4.6 African savannas are threatened by livestock overgrazing and conversion to farmland. Photograph by W. F. Laurance.4.3.3 Grasslands and deserts in recent decades, and rates of loss remain very high (Klink and Machado 2005).Grasslands and desert areas have generally suf-fered to a lesser extent than forests (Figure 4.4).Just 10–20% of all grasslands, which include the 4.3.4 Boreal and alpine regionssavannas of Africa (Figure 4.6), the llano and cer-rado ecosystems of South America, the steppes of Boreal forests are mainly found in broad conti-Central Asia, the prairies of North America, and nental belts at the higher latitudes of Norththe spinifex grasslands of Australia, have been America and Eurasia. They are vast in Siberia,permanently destroyed for agriculture (White the largest contiguous forest area in the world,et al. 2000; Kauffman and Pyke 2001). About a as well as in northern Canada. They also occur atthird of the world’s deserts have been converted high elevations in more southerly areas, such asto other land uses (Figure 4.4). Included in this the European Alps and Rocky Mountains offigure is the roughly 9 million km2 of seasonally North America. Dominated by evergreen coni-dry lands, such as the vast Sahel region of Africa, fers, boreal forests are confined to cold, moistthat have been severely degraded via desertifica- climates and are especially rich in soil carbon,tion (Primack 2006). because low temperatures and waterlogged soils Although deserts and grasslands have not inhibit decomposition of organic material (Mat-fared as badly as some other biomes, certain re- thews et al. 2000).gions have suffered very heavily. For instance, Habitat loss in boreal forests has historicallyless than 3% of the tallgrass prairies of North been low (Figure 4.4; Box 4.2). In Russia, howev-America survive, with the remainder having er, legal and illegal logging activity has grownbeen converted to farmland (White et al. 2000). rapidly, with Siberia now a major source of tim-In southern Africa, large expanses of dryland are ber exports to China, the world’s largest timberbeing progressively desertified from overgrazing importer. In Canada, nearly half of the borealby livestock (MEA 2005). In South America, more forest is under tenure for wood production. Inthan half of the biologically-rich cerrado savannas, addition, fire incidence is high in the borealwhich formerly spanned over 2 million km2, have zone, with perhaps 100 000 km2 of boreal forestbeen converted into soy fields and cattle pastures burning each year (Matthews et al. 2000).© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 95. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL Like boreal forests, tundra is a vast ecosystem such as taiga grasslands (Figure 4.7), have also(spanning 9–13 million km2 globally) that has suffered little loss. However, all boreal ecosystemsbeen little exploited historically (Figure 4.4) are vulnerable to global warming (see Chapter 8;(White et al. 2000). Unlike permafrost areas, tun- Box 4.2). Boreal forests, in particular, could declinedra ecosystems thaw seasonally on their surface, if climatic conditions become significantly warm-becoming important wetland habitats for water- er or drier, leading to an increased frequency orfowl and other wildlife. Other boreal habitats, severity of forest fires (see Box 4.2, Chapter 9). Box 4.2 Boreal forest management: harvest, natural disturbance, and climate change Ian G. Warkentin Until recently, the boreal biome has largely been rise in human‐ignited fires has led to a 2.3% ignored in discussions regarding the global annual decrease in forest cover (Achard et al. impacts of habitat loss through diminishing 2006, 2008). forest cover. Events in tropical regions during the past four decades were far more critical due to the high losses of forest and associated species (Dirzo and Raven 2003). While there are ongoing concerns about tropical forest harvest, the implications of increasing boreal forest exploitation now also need to be assessed, particularly in the context of climate change. (Bradshaw et al. 2009) Warnings suggest that forest managers should not overlook the services provided by the boreal ecosystem, especially carbon storage (Odling‐Smee 2005). Ranging across northern Eurasia and North America, the boreal biome constitutes one third of all current forest cover on Earth and is home to nearly half Box 4.2 Figure An example of harvesting in the Boreal forest. of the remaining tracts of extensive, intact Photograph by Greg Mitchell. forests. Nearly 30% of the Earth’s terrestrial The biggest challenge for boreal managers stored carbon is held here, and the boreal may may come from the warmer and drier weather, well have more influence on mean annual global with a longer growing season, that climate temperature than any other biome due to its change models predict for upper‐latitude sunlight reflectivity (albedo) properties and ecosystems (IPCC 2001). The two major drivers evapotranspiration rates (Snyder et al. 2004). of boreal disturbance dynamics (fire and insect Conversion of North America’s boreal forest to infestation) are closely associated with weather other land cover types has been limited (e.g. 3% conditions (Soja et al. 2007) and predicted to be in Canada; Smith and Lee 2000). In Finland and both more frequent and intense over the next Sweden forest cover has expanded during recent century (Kurz et al. 2008); more human‐ignited decades, but historic activities extensively reduced fires are also predicted as access to the forest and modified the region’s boreal forests for expands (Achard et al. 2008). Increased harvest, commercial purposes, leaving only a small fire and insect infestations will raise the rates of proportion as natural stands (Imbeau et al. 2001; carbon loss to the atmosphere, but climate see Box 4.2 Figure). Conversely, there has been a models also suggest that changes to albedo and rapid expansion of harvest across boreal Russia evapotranspiration due to these disturbances during the past 10–15 years leading to broad will offset the lost carbon stores (Bala et al. shifts from forest to other land cover types (MEA 2007)—maintaining large non‐forested boreal 2005). Forest cover loss across European Russia is sites potentially may cool the global climate associated with intensive harvest, mineral more than the carbon storage resulting from exploitation and urbanization, while in Siberian reforestation at those sites. However, to Russia the combination of logging and a sharp manage the boreal forest based solely on one continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 96. 1 HABITAT DESTRUCTION: DEATH BY A THOUSAND CUTS 81 Box 4.2 (Continued) ecosystem service would be reckless. For Imbeau, L., Mönkkönen, M., and Desrochers, A. (2001). example, many migratory songbirds that Long‐term effects of forestry on birds of the depend upon intact boreal forest stands for eastern Canadian boreal forests: a comparison breeding also provide critical services such as with Fennoscandia. Conservation Biology, 15, insect predation, pollen transport and seed 1151–1162. dispersal (Sekercioglu 2006) in habitats IPCC (Intergovernmental Panel on Climate Change) extending from boreal breeding grounds, to (2001). Climate change 2001: the scientific basis. migratory stopovers and their winter homes Contribution of Working Group I to the Third in sub‐tropical and tropical regions. Thus Assessment Report of the Intergovernmental Panel boreal forest managers attempting to meet on Climate Change. Cambridge University Press, climate change objectives (or any other single New York, NY. goal) must also consider the potential costs Kurz, W. A., Stinson, G., Rampley, G. J., Dymond, C. C., for biodiversity and the multiple services at and Neilson, E. T. (2008). Risk of natural disturbances risk due to natural and human‐associated makes future contribution of Canada’s forests to the change. global carbon cycle highly uncertain. Proceedings of the National Academy of Sciences of the United States of REFERENCES America, 105, 1551–1555. MEA (Millennium Ecosystem Assessment) (2005). Achard, F., Mollicone, D., Stibig, H.‐J., et al. (2006). Areas Ecosystems and human well‐being: synthesis. Island of rapid forest‐cover change in boreal Eurasia. Forest Press, Washington, DC. Ecology and Management, 237, 322–334. Odling‐Smee, L. (2005). Dollars and sense. Nature, 437, Achard, F. D., Eva, H. D., Mollicone, D., and Beuchle, R. 614–616. (2008). The effect of climate anomalies and human Sekercioglu, C. H. (2006). Increasing awareness of avian ignition factor on wildfires in Russian boreal forests. ecological function. Trends in Ecology and Evolution, 21, Philosophical Transactions of the Royal Society of 464–471. London B, 363, 2331–2339. Smith, W. and Lee, P., eds (2000). Canada’s forests at a Bala, G., Caldeira, K., Wickett, M., et al. (2007). Combined crossroads: an assessment in the year 2000. World climate and carbon‐cycle effects of large‐scale defores- Resources Institute, Washington, DC. tation. Proceedings of the National Academy of Sciences Snyder, P. K., Delire, C., and Foley, J. A. (2004). of the United States of America, 104, 6550–6555. Evaluating the influence of different vegetation Bradshaw, C. J. A., Warkentin, I. G., and Sodhi, N. S. (2009). biomes on the global climate. Climate Dynamics, Urgent preservation of boreal carbon stocks and biodi- 23, 279–302. versity. Trends in Ecology and Evolution, 24, 541–548. Soja, A. J., Tchebakova, N. M., French, N. H. F., et al. Dirzo, R. and Raven, P. H. (2003). Global state of biodi- (2007). Climate‐induced boreal forest change: versity and loss. Annual Review of Environment and Predictions versus current observations. Global and Resources, 28, 137–167 Planetary Change, 56, 274–296.In addition, tundra areas will shrink as boreal destroyed in the last two centuries (Stein et al.forests spread north. 2000). From 60–70% of all European wetlands have been destroyed outright (Ravenga et al. 2000). Many developing nations are now4.3.5 Wetlands suffering similarly high levels of wetland loss,Although they do not fall into any single biome particularly as development in coastal zones ac-type, wetlands have endured intense habitat de- celerates. As discussed above, losses of mangrovestruction in many parts of the world. In the USA, forests, which are physiologically specialized forfor instance, over half of all wetlands have been the intertidal zone, are also very high.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 97. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL somewhat. Forest cover is now increasing in east- ern and western North America, Alaska, western and northern Europe, eastern China, and Japan (Matthews et al. 2000; MEA 2005, Figure 4.4). During the 1990s, for instance, forest cover rose by around 29 000 km2 annually in the temperate and boreal zones, although roughly 40% of this increase comprised forest plantations of mostly non-native tree species (MEA 2005). Despite par- tial recovery of forest cover in some regions (Wright and Muller-Landau 2006), conversion rates for many ecosystems, such as tropical and subtropical forests and South American cerrado savanna-woodlands, remain very high. Because arable land is becoming scarce while agricultural demands for food and biofuel feed- stocks are still rising markedly (Koh and Ghazoul 2008), agriculture is becoming increasingly inten- sified in much of the world. Within agricultural regions, a greater fraction of the available land is actually being cultivated, the intensity of cultiva- tion is increasing, and fallow periods are decreas- ing (MEA 2005). Cultivated systems (where over 30% of the landscape is in croplands, shifting cultivation, confined-livestock production, orFigure 4.7 Boreal ecosystems, such as this alpine grassland in New freshwater aquaculture) covered 24% of the glob-Zealand, have suffered relatively little habitat loss but are particularlyvulnerable to global warming. Photograph by W. F. Laurance. al land surface by the year 2000 (Figure 4.2). Thus, vast expanses of the earth have been al- tered by human activities. Old-growth forests have4.4 Land-use intensification diminished greatly in extent in many regions, es-and abandonment pecially in the temperate zones; for instance, atHumans have transformed a large fraction of the least 94% of temperate broadleaf forests haveEarth’s land surface (Figure 4.2). Over the past been disturbed by farming and logging (Primackthree centuries, the global extent of cropland has 2006). Other ecosystems, such as coniferous forests,risen sharply, from around 2.7 to 15 million km2, are being rapidly converted from old-growth tomostly at the expense of forest habitats (Turner semi-natural production forests with a simplifiedet al. 1990). Permanent pasturelands are even stand structure and species composition. Forestmore extensive, reaching around 34 million km2 cover is increasing in parts of the temperate andby the mid-1990s (Wood et al. 2000). The rate of boreal zones, but the new forests are secondaryland conversion has accelerated over time: for and differ from old-growth forests in species com-instance, more land was converted to cropland position, structure, and carbon storage. Yet otherfrom 1950 to 1980 than from 1700 to 1850 (MEA ecosystems, particularly in the tropics, are being2005). rapidly destroyed and degraded. For example, ma- Globally, the rate of conversion of natural ha- rine ecosystems have been heavily impacted bybitats has finally begun to slow, because land human activities (see Box 4.3).readily convertible to new arable use is now in The large-scale transformations of landincreasingly short supply and because, in temper- cover described here consider only habitat lossate and boreal regions, ecosystems are recovering per se. Of the surviving habitat, much is being© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 98. 1 HABITAT DESTRUCTION: DEATH BY A THOUSAND CUTS 83 Box 4.3 Human Impacts on marine ecosystems Benjamin S. Halpern, Carrie V. Kappel, Fiorenza Micheli, and Kimberly A. Selkoe The oceans cover 71% of the planet. This salt marshes. Effects from climate change, such vastness has led people to assume ocean as rising sea levels and temperatures and ocean resources are inexhaustible, yet evidence to the acidification, are observed with increasing contrary has recently accumulated (see Box 4.3 frequency around the world. Global commerce, Figure 1 and Plate 4). Populations of large fish, aquaculture and the aquarium trade have mammals, and sea turtles have collapsed due to caused the introduction of thousands of non‐ intense fishing pressure, putting some species native species, many of which become at risk of extinction, and fishing gear such as ecologically and economically destructive in bottom trawls not only catch target fish but their new environment. These human‐caused also destroy vast swaths of habitat (see Box 6.1). stresses on ocean ecosystems are the most Pollution, sedimentation, and nutrient intense and widespread, but many other enrichment have caused die‐offs of fish and human activities impact the ocean where they corals, blooms of jellyfish and algae, and “dead are concentrated, such as shipping, zones” of oxygen‐depleted waters around the aquaculture, and oil and gas extraction, and world. Coastal development has removed much many new uses such as wave and wind energy of the world’s mangroves, sea grass beds and farms are just emerging. Box 4.3 Figure 1 A few of the many human threats to marine ecosystems around the world. (A) The seafloor before and after bottom trawl fishing occurred [courtesy CSIRO (Australian Commonwealth Scientific and Research Organization) Marine Research], (B) coastal development in Long Beach, California (courtesy California Coastal Records Project), (C) shrimp farms in coastal Ecuador remove coastal habitat (courtesy Google Earth), and (D) commercial shipping and ports produce pollution and introduce non‐native species (courtesy public commons). There are clear challenges in reducing the synergisms among stressors that can amplify impacts of any single human activity on marine impacts. For example, excess nutrient input ecosystems. These challenges are particularly combined with overfishing of herbivorous fish stark in areas where dozens of activities co‐ on coral reefs can lead to algal proliferation occur because each species and each ecosystem and loss of coral with little chance of recovery, may respond uniquely to each set of human while each stressor alone may not lead to such activities, and there may be hard‐to‐predict an outcome. The majority of oceans are subject continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 99. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALL Box 4.3 (Continued) to at least three different overlapping human Table). The heaviest impacts occur in the North stressors, with most coastal areas experiencing Sea and East and South China Seas, where over a dozen, especially near centers of industry, dense human population, and a long commerce like the ports of Los Angeles and history of ocean use come together. The least Singapore. impacted areas are small and scattered The first comprehensive map of the impacts of throughout the globe, with the largest patches 17 different types of human uses on the global at the poles and the Torres Strait north of oceans provides information on where Australia. Several of the countries whose seas are cumulative human impacts to marine ecosystems significantly impacted, including the United are most intense (Halpern et al. 2008; see Box 4.3 States and China, have huge territorial holdings, Figure 2 and Plate 5). The map shows that over suggesting both a responsibility and an 40% of the oceans are heavily impacted and less opportunity to make a significant difference in than 4% are relatively pristine (see Box 4.3 improving ocean health. Very Low Impact (2.4) Medium Impact (5.7–9.0) High Impact (12.3–15.5) Low Impact (2.4–5.7) Medium High Impact (9.0–12.3) Very High Impact (15.5) Box 4.3 Figure 2 Global map of the cumulative human impact on marine ecosystems, based on 20 ecosystem types and 17 different human activities. Grayscale colors correspond to overall condition of the ocean as indicated in the legend, with cumulative impact score cutoff values for each category of ocean condition indicated. continues© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 100. 1 HABITAT DESTRUCTION: DEATH BY A THOUSAND CUTS 85 Box 4.3 (Continued) Box 4.3 Table The amount of marine area within the Exclusive Economic Zone (EEZ) of countries that is heavily impacted. Countries are listed in order of total marine area within a country’s EEZ (including territorial waters) and includes a selection of countries chosen for illustrative purposes. Global statistics are provided for comparison. Data are drawn from Halpern et al. (2008). Country % of global ocean area Impact Category Very Medium‐ Very Low Low Medium High High High GLOBAL 100% 3.7% 24.5% 31.3% 38.2% 1.8% 0.5% Largest EEZs United States 3.3% 2.0% 9.1% 21.5% 62.1% 4.4% 0.7% France 2.8% 0.2% 36.7% 40.1% 21.6% 0.9% 0.4% Australia 2.5% 3.7% 26.4% 42.3% 26.3% 1.0% 0.3% Russia 2.1% 22.5% 30.8% 32.3% 13.5% 0.6% 0.3% United Kingdom 1.9% 0.3% 25.2% 36.0% 29.0% 6.5% 3.0% Indonesia 1.7% 2.3% 32.0% 42.4% 18.0% 3.0% 2.1% Canada 1.5% 22.8% 18.4% 25.8% 26.5% 5.5% 1.0% Japan 1.1% 0.0% 0.9% 9.7% 76.2% 9.9% 3.2% Brazil 1.0% 3.1% 17.1% 32.4% 44.8% 2.1% 0.5% Mexico 0.9% 1.2% 29.1% 32.7% 35.5% 1.2% 0.3% India 0.6% 0.1% 7.3% 32.9% 51.4% 6.8% 1.5% China 0.2% 0.0% 24.5% 5.7% 27.2% 20.1% 22.5% SMALLER EEZs Germany 0.02% 0.4% 43.7% 2.4% 34.6% 14.4% 4.4% Iceland 0.21% 0.0% 0.4% 10.1% 58.4% 26.3% 4.8% Ireland 0.11% 0.0% 0.2% 2.2% 50.3% 40.8% 6.6% Italy 0.15% 0.0% 3.5% 15.5% 64.5% 11.8% 4.7% Netherlands 0.04% 0.0% 18.6% 3.6% 68.8% 7.7% 1.5% Sri Lanka 0.15% 0.0% 2.5% 8.6% 45.0% 37.2% 6.7% Thailand 0.08% 0.4% 21.9% 42.6% 22.1% 9.6% 3.4% Vietnam 0.18% 1.1% 21.0% 26.7% 35.7% 10.2% 5.4% Complex but feasible management of marine ecosystems. Ultimately, it is now clear approaches are needed to address the that marine resources are not inexhaustible cumulative impacts of human activities on the and that precautionary, multi‐sector planning oceans. Comprehensive spatial planning of of their use is needed to ensure long‐term activities affecting marine ecosystems, or ocean sustainability of marine ecosystems and the zoning, has already been adopted and crucial services they provide. implemented in Australia’s Great Barrier Reef and parts of the North Sea, with the goal of minimizing the overlap and potential synergies of multiple stressors. Many countries, including the United States, are beginning to adopt REFERENCES Ecosystem‐Based Management (EBM) Halpern, B. S., Walbridge, S., Selkoe, K. A., et al. (2008). A approaches that explicitly address cumulative global map of human impact on marine ecosystems. impacts and seek to balance sustainable use of Science, 319, 948–952. the oceans with conservation and restoration© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 101. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLdegraded in various ways—such as by habitat Suggested readingfragmentation, increased edge effects, selectivelogging, pollution, overhunting, altered fireregimes, and climate change. These forms of · Sanderson, E. W., Jaiteh, M., Levy, M., Redford, K., Wan- nebo, A., and Woolmer, G. (2002). The human footprint and the last of the wild. BioScience, 52, 891–904.environmental degradation, as well as the impor-tant environmental services these ecosystems pro- · Sodhi, N.S., Koh, L P., Brook, B.W., and Ng, P. (2004). Southeast Asian biodiversity: an impending catastro-vide, are discussed in detail in subsequent phe. Trends in Ecology and Evolution, 19, 654–660.chapters. · MEA. (2005). Millennium Ecosystem Assessment. Ecosys- tems and Human Well-Being: Synthesis. Island Press, Wa- shington, DC.Summary· Vast amounts of habitat destruction have already · Laurance, W.F. and Peres, C. A., eds. (2006). Emerging Threats to Tropical Forests. University of Chicago Press,occurred. For instance, about half of all global forest Chicago.cover has been lost, and forests have virtually van-ished in over 50 nations worldwide. Relevant websites· Habitat destruction has been highly unevenamong different ecosystems. From a geographic per- · Mongabay:, islands, coastal areas, wetlands, regionswith large or growing human populations, and · · Forest Protection Portal: The Millennium Ecosystem Assessment synthesis re-emerging agricultural frontiers are all sustaining ports: habitat loss.· From a biome perspective, habitat loss has beenvery high in Mediterranean forests, temperate for- REFERENCESest-steppe and woodland, temperate broadleaf for- Achard, F., Eva, H., Stibig, H., Mayaux, P., Gallego, J.,ests, and tropical coniferous forests. Other Richards, T., and Malingreau, J.-P. (2002). Determinationecosystems, particularly tropical rainforests, are of deforestation rates of the world’s humid tropicalnow disappearing rapidly. forests. Science, 297, 999–1002.· Habitat destruction in the temperate zone peakedin the 19th and early 20th centuries. Although con- Cincotta, R. P., Wisnewski, J., and Engelman, R. (2000). Human population in the biodiversity hotspots. Nature, 404, 990–2.siderable habitat loss is occurring in some temperate Curran, L. M., Trigg, S., McDonald, A., et al. (2004). Low-ecosystems, overall forest cover is now increasing land forest loss in protected areas of Indonesian Borneo.from forest regeneration and plantation establish- Science, 303, 1000–1003.ment in some temperate regions. Danielsen, F., Srensen, M. K., Olwig, M. F. et al. (2005).· Primary (old-growth) habitats are rapidly dimin-ishing across much of the earth. In their place, a The Asian Tunami: A protective role for coastal vegeta- tion. Science, 310, 643.variety of semi-natural or intensively managed eco- FAO (Food and Agriculture Organization Of The Unitedsystems are being established. For example, al- Nations) (2000). Global forest resource assessment 2000—though just two-tenths of the temperate coniferous main report. FAO, New York.forests have disappeared, vast areas are being con- Kauffman, J. B. and Pyke, D. A. (2001). Range ecology, global livestock influences. In S. Levin, ed. Encyclopedia of biodi-verted from old-growth to timber-production for- versity 5, pp. 33–52. Academic Press, San Diego, California.ests, with a greatly simplified stand structure and Klink, C. A. and Machado, R. B. (2005). Conservation of thespecies composition.· Boreal ecosystems have suffered relativelylimited reductions to date but are especially vulner- Brazilian cerrado. Conservation Biology, 19, 707–713. Koh, L. P. and Ghazoul, J. (2008). Biofuels, biodiversity, and people: understanding the conflicts and finding op-able to global warming. Boreal forests could become portunities. Biological Conservation, 141, 2450–2460.increasingly vulnerable to destructive fires if future Koh, L. P. and Wilcove, D. S. (2008). Is oil palm agricultureconditions become warmer or drier. really destroying biodiversity. Conservation Letters, 1, 60–64.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 102. 1 HABITAT DESTRUCTION: DEATH BY A THOUSAND CUTS 87Laurance, W. F. (1999). Reflections on the tropical defores- wetland ecosystems. World Resources Institute, tation crisis. Biological Conservation, 91, 109–117. Washington, DC.Laurance, W. F. (2007). Forest destruction in tropical Asia. Sekercioglu C. H., Ehrlich, P. R., Daily, G. C., Aygen, D., Current Science, 93, 1544–1550. Goehring, D., and Sandi, R. (2002). Disappearance ofLaurance, W. F., Albernaz, A., and Da Costa, C. (2001). Is insectivorous birds from tropical forest fragments. Pro- deforestation accelerating in the Brazilian Amazon? En- ceedings of the National Academy of Sciences of the United vironmental Conservation, 28, 305–11. States of America, 99, 263–267.Laurance, W. F., Lovejoy, T., Vasconcelos, H., et al. (2002). Sodhi, N. S., Koh, L. P., Brook, B. W., and Ng, P. (2004). Ecosystem decay of Amazonian forest fragments: a 22- Southeast Asian biodiversity: an impending disaster. year investigation. Conservation Biology, 16, 605–618. Trends in Ecology and Evolution, 19, 654–660.MacKinnon, K. (2006). Megadiversity in crisis: politics, Stein, B. A., Kutner, L. and Adams, J., eds (2000). Precious policies, and governance in Indonesia’s forests. In W. F. heritage: the status of biodiversity in the United States. Laurance and C. A. Peres, eds Emerging threats to tropical Oxford University Press, New York. forests, pp. 291–305. University of Chicago Press, Chicago, Turner, B. L., Clark, W. C., Kates, R., Richards, J., Mathews J., Illinois. and Meyer, W., eds (1990). The earth as transformed by humanMatthews, E., Rohweder, M., Payne, R., and Murray, S. action: global and regional change in the biosphere over the past (2000). Pilot Analysis of Global Ecosystems: Forest Ecosys- 300 years. Cambridge University Press, Cambridge, UK. tems. World Resources Institute, Washington, DC. White, R. P., Murray, S., and Rohweder, M. (2000) PilotMayaux, P., Holmgren, P., Achard, F., Eva, H., Stibig, H.-J., analysis of global ecosystems: grassland ecosystems. World and Branthomme, A. (2005). Tropical forest cover change Resources Institute, Washington, DC. in the 1990s and options for future monitoring. Philosophical Whitmore, T. C. (1997). Tropical forest disturbance, Transactions of the Royal Society of London B, 360, 373–384. disappearance, and species loss. In Laurance,MEA (Millenium Ecosystem Assessment) (2005). Ecosys- W. F. and R. O. Bierregaard, eds Tropical forest Remnants: tems and human well-being: synthesis. Island Press, Wa- ecology, management, and conservation of fragmented shington, DC. communities, pp. 3–12. University of Chicago Press,Myers, N., Mittermeier, R., Mittermeier, C., Fonseca, G., Chicago, Illinois. and Kent, J. (2000). Biodiversity hotspots for conserva- Wood, S., Sebastian, K., and Scherr, S. J. (2000). Pilot analy- tion priorities. Nature, 403, 853–858. sis of global ecosystems: agroecosystems. World ResourcesPimm, S. L. and Raven, P. (2000). Biodiversity: Extinction Institute, Washington, DC. by numbers. Nature, 403, 843–845. WRI (World Resources Institute) (2003). World resourcesPrimack, R. B. (2006). Essentials of conservation biology, 4th 2002–2004: decisions for the earth: balance, voice, and edn. Sinauer Associates, Sunderland, Massachusetts. power. World Resources Institute, Washington, DC.Ravenga, C., Brunner, J., Henninger, N., Kassem, K., and Wright, S. J. and Muller-Landau, H. C. (2006). The future of Payne, R. (2000). Pilot analysis of global ecosystems: tropical forest species. Biotropica, 38, 287–301.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 103. Sodhi and Ehrlich: Conservation Biology for All. CHAPTER 5 Habitat fragmentation and landscape change Andrew F. Bennett and Denis A. SaundersBroad-scale destruction and fragmentation of fragmentation” for issues directly associated withnative vegetation is a highly visible result the subdivision of vegetation and its ecologicalof human land-use throughout the world (Chap- consequences.ter 4). From the Atlantic Forests of South America This chapter begins by summarizing the con-to the tropical forests of Southeast Asia, and in ceptual approaches used to understand conserva-many other regions on Earth, much of the original tion in fragmented landscapes. We then examinevegetation now remains only as fragments the biophysical aspects of landscape change, andamidst expanses of land committed to feeding how such change affects species and commu-and housing human beings. Destruction and nities, posing two main questions: (i) what arefragmentation of habitats are major factors in the implications for the patterns of occurrence ofthe global decline of populations and species species and communities?; and (ii) how does(Chapter 10), the modification of native plant and landscape change affect processes that influenceanimal communities and the alteration of ecosys- the distribution and viability of species and com-tem processes (Chapter 3). Dealing with these munities? The chapter concludes by identifyingchanges is among the greatest challenges facing the kinds of actions that will enhance the conser-the “mission-orientated crisis discipline” of conser- vation of biota in fragmented landscapes.vation biology (Soulé 1986; see Chapter 1). Habitat fragmentation, by definition, is the“breaking apart” of continuous habitat, such as 5.1 Understanding the effectstropical forest or semi-arid shrubland, into dis- of landscape changetinct pieces. When this occurs, three interrelatedprocesses take place: a reduction in the total 5.1.1 Conceptual approachesamount of the original vegetation (i.e. habitat The theory of island biogeography (MacArthurloss); subdivision of the remaining vegetation and Wilson 1967) had a seminal influence in sti-into fragments, remnants or patches (i.e. habitat mulating ecological and conservation interest infragmentation); and introduction of new forms of fragmented landscapes. This simple, elegantland-use to replace vegetation that is lost. These model highlighted the relationship between thethree processes are closely intertwined such that number of species on an island and the island’sit is often difficult to separate the relative effect of area and isolation. It predicted that species rich-each on the species or community of concern. ness on an island represents a dynamic balanceIndeed, many studies have not distinguished be- between the rate of colonization of new species totween these components, leading to concerns that the island and the rate of extinction of species“habitat fragmentation” is an ambiguous, or even already present. It was quickly perceived thatmeaningless, concept (Lindenmayer and Fischer habitat isolates, such as forest fragments, could2006). Consequently, we use “landscape change” also be considered as “islands” in a “sea” of de-to refer to these combined processes and “habitat veloped land and that this theory provided a88© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 104. 1 HABITAT FRAGMENTATION AND LANDSCAPE CHANGE 89quantitative approach for studying their biota. live fences, and pastures with dispersed treesThis stimulated many studies in which species each support diverse assemblages of birds, bats,richness in fragments was related to the area dung beetles and butterflies (Harvey et al. 2006).and isolation of the fragment, the primary factors To these species, the landscape represents a mo-in island biogeographic theory. saic of land uses of differing quality, rather than a The development of landscape ecology contrib- contrast between “habitat” and “non-habitat”.uted new ways of thinking about habitat Recognizing landscapes as mosaics emphasizesfragments and landscape change. The concept the need to appreciate all types of elements inof patches and connecting corridors set within the landscape. This perspective is particularly rel-a matrix (i.e. the background ecosystem or evant in regions where cultural habitats, derivedland-use type) became an influential paradigm from centuries of human land-use, have impor-(Forman and Godron 1986). It recognized the tant conservation values.importance of the spatial context of fragments. Different species have different ecologicalThe environment surrounding fragments is great- attributes, such as their scale of movement, life-ly modified during landscape changes associated history stages, longevity, and what constituteswith fragmentation. Thus, in contrast to islands, habitat. These each influence how a species “per-fragments and their biota are strongly influenced ceives” a landscape, as well as its ability toby physical and biological processes in the wider survive in a modified landscape. Consequently,landscape, and the isolation of fragments de- the same landscape may be perceived bypends not only on their distance from a similar different taxa as having a different structure andhabitat but also on their position in the landscape, different suitability, and quite differently fromthe types of surrounding land-uses and how they the way that humans describe the landscape.influence the movements of organisms (Saunders A “species-centered” view of a landscape can beet al. 1991; Ricketts 2001). obtained by mapping contours of habitat suitabil- The influence of physical processes and distur- ity for any given species (Fischer et al. 2004).bance regimes on fragments means that followinghabitat destruction and fragmentation, habitat 5.1.2 Fragment vs landscape perspectivemodification also occurs. Mcintyre and Hobbs(1999) incorporated this complexity into a con- Habitat fragmentation is a landscape-level pro-ceptual model by outlining four stages along a cess. Fragmented landscapes differ in the sizetrajectory of landscape change. These were: and shape of fragments and in their spatial con-(i) intact landscapes, in which most original veg- figuration. Most “habitat fragmentation” studiesetation remains with little or no modification; have been undertaken at the fragment level, with(ii) variegated landscapes, dominated by the orig- individual fragments as the unit of study. How-inal vegetation, but with marked gradients of ever, to draw inferences about the consequenceshabitat modification; (iii) fragmented landscapes, of landscape change and habitat fragmentation, itin which fragments are a minor component in is necessary to compare “whole” landscapesa landscape dominated by other land uses; and that differ in their patterns of fragmentation(iv) relict landscapes with little (10%) cover of (McGarigal and Cushman 2002). Comparisonsoriginal vegetation, set within highly modified of landscapes are also important because: (i) land-surroundings. This framework emphasizes the scapes have properties that differ from thosedynamics of landscape change. Different stages of fragments (Figure 5.1); (ii) many speciesalong the trajectory pose different kinds of chal- move between and use multiple patches in thelenges for conservation management. landscape; and (iii) conservation managers must Many species are not confined solely to frag- manage entire landscapes (not just individualments, but also occur in other land uses in mod- fragments) and therefore require an understand-ified landscapes. In Nicaragua, for example, ing of the desirable properties of whole land-riparian forests, secondary forests, forest fallows, scapes. Consequently, it is valuable to consider© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 105. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLa) b) many of these are intercorrelated, especially with the total amount of habitat remaining in the land- scape (Fahrig 2003). Several aspects of the spatial configuration of fragments that usefully distinguish between different landscapes include: (i) the degree of subdivision (i.e. number of fragments), (ii) the aggregation of habitat, and (iii) the complexity of fragment shapes (Figure 5.3). Some kinds of changes are not necessarily evi- dent from a time-series sequence. Landscape change is not random: rather, disproportionateIndividual fragments Whole landscapessize compositional gradients change occurs in certain areas. Clearing of vegeta-shape diversity of land-uses tion is more common in flatter areas at lower eleva-core area number of fragments tions and on the more-productive soils. Such areasvegetation type aggregation are likely to retain fewer, smaller fragments of orig-isolation structural connectivity inal vegetation, whereas larger fragments are moreFigure 5.1 Comparison of the types of attributes of a) individual likely to persist in areas less suitable for agriculturalfragments and b) whole landscapes. or urban development, such as on steep slopes, poorer soils, or regularly inundated floodplains.the consequences of landscape change at both the This has important implications for conservationfragment and landscape levels. because sites associated with different soil types and elevations typically support different sets of species. Thus, fragments usually represent a biased sample of the former biota of a region. There also is5.2 Biophysical aspects of landscape a strong historical influence on landscape changechange because many fragments, and the disturbance re-5.2.1 Change in landscape pattern gimes they experience, are a legacy of past land settlement and land-use (Lunt and Spooner 2005).Landscape change is a dynamic process. A series of Land-use history can be an effective predictor of the“snapshots” at intervals through time (Figure 5.2) present distribution of fragments and ecosystemillustrates the pattern of change to the original condition within fragments. It is necessary to un-vegetation. Characteristic changes along a time derstand ecological processes and changes in thetrajectory include: (i) a decline in the total area of past in order to manage for the future.fragments; (ii) a decrease in the size of many frag-ments (large tracts become scarce, small fragmentspredominate); (iii) increased isolation of fragments 5.2.2 Changes to ecosystem processesfrom similar habitat; and (iv) the shapes of frag- Removal of large tracts of native vegetationments increasingly become dominated by straight changes physical processes, such as those relatingedges compared with the curvilinear boundaries of to solar radiation and the fluxes of wind and waternatural features such as rivers. For small fragments (Saunders et al. 1991). The greatest impact on frag-and linear features such as fencerows, roadside ments occurs at their boundaries; small remnantsvegetation, and riparian strips, the ratio of perime- and those with complex shapes experience theter length to area is high, resulting in a large pro- strongest “edge effects”. For example, the micro-portion of “edge” habitat. An increase in the climate at a forest edge adjacent to cleared landoverall proportion of edge habitat is a highly influ- differs from that of the forest interior in attributesential consequence of habitat fragmentation. such as incident light, humidity, ground and air At the landscape level, a variety of indices have temperature, and wind speed. In turn, these phys-been developed to quantify spatial patterns, but ical changes affect biological processes such as© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 106. 1 HABITAT FRAGMENTATION AND LANDSCAPE CHANGE 91Figure 5.2 Changes in the extent and pattern of native vegetation in the Kellerberrin area, Western Australia, from 1920 to 1984, illustrating theprocess of habitat loss and fragmentation. Reprinted from Saunders et al. (1993).litter decomposition and nutrient cycling, and the of disturbance-adapted butterflies and beetlesstructure and composition of vegetation. and elevated tree mortality extend 200 m or Changes to biophysical processes from land use more from the forest edge (Laurance 2008). Inin the surrounding environment, such as the use of most situations, changes at edges are generallyfertilizers on farmland, alterations to drainage pat- detrimental to conservation values because theyterns and water flows, and the presence of exotic modify formerly intact habitats. However, inplants and animals, also have spill-over effects in some circumstances edges are deliberately man-fragments. Many native vegetation communities aged to achieve specific outcomes. Manipula-are resistant to invasion by exotic plant species tion of edges is used to enhance the abundanceunless they are disturbed. Grazing by domestic of game species such as deer, pheasants andstock and altered nutrient levels can facilitate the grouse (see Box 1.1). In England, open linearinvasion of exotic species of plants, which mark- “rides” in woods may be actively managed toedly alters the vegetation in fragments (Hobbs and increase incident light and early successional habi-Yates 2003) and habitats for animals. tat for butterflies and other wildlife (Ferris-Kaan The intensity of edge effects in fragments and 1995).the distance over which they act varies between Changes to biophysical processes frequentlyprocesses and between ecosystems. In tropical have profound effects for entire landscapes. Inforests in the Brazilian Amazon, for example, highly fragmented landscapes in which mostchanges in soil moisture content, vapor pressure fragments are small or have linear shapes, theredeficit, and the number of treefall gaps extend may be little interior habitat that is buffered fromabout 50 m into the forest, whereas the invasion edge effects. Changes that occur to individual© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 107. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLfragments accumulate across the landscape. 5.3 Effects of landscape change on speciesChanges to biophysical processes such as hydro- Species show many kinds of responses to habitatlogical regimes can also affect entire landscapes. fragmentation: some are advantaged and in-In the Western Australian wheatbelt (Figure 5.2), crease in abundance, while others decline andmassive loss of native vegetation has resulted in a become locally extinct (see Chapter 10). Under-rise in the level of groundwater, bringing stored standing these diverse patterns, and the processessalt (NaCl) to the surface where it accumulates underlying them, is an essential foundation forand reduces agricultural productivity and trans- conservation. Those managing fragmentedforms native vegetation (Hobbs 1993). Box 5.1 Time lags and extinction debt in fragmented landscapes Andrew F. Bennett and Denis A. Saunders Habitat destruction and fragmentation result 7 in immediately visible and striking changes to the pattern of habitat in the landscape. 6 However, the effects of these changes on the Species richness 5 biota take many years to be expressed: there is a time‐lag in experiencing the full 4 consequences of such habitat changes. Long‐ lived organisms such as trees may persist for 3 many decades before disappearing without 2 replacement; small local populations of animals gradually decline before being lost; and 1 ecological processes in fragments are sensitive 0 to long‐term changes in the surroundings. 1 10 100 1000 Conservation managers cannot assume that Area (ha) species currently present in fragmented landscapes will persist there. Many fragments Box 5.1 Figure A change in the species‐area relationship for and landscapes face impending extinctions, mammals in rainforest fragments in Queensland, Australia, between 1986 (filled circles) and 2006 (open circles) illustrates a time‐lag in even though there may be no further change in the loss of species following fragmentation. Data from Laurance fragment size or the amount of habitat in the et al. (2008). landscape. We are still to pay the ‘extinction debt’ for the consequences of past actions. declined further (see Box 5.1 Figure), with most Identifying the duration of time‐lags and declines in the smaller fragments. By 2006–07, forecasting the size of the extinction debt for one species, the lemuroid ringtail possum fragmented landscapes is difficult. The clearest (Hemibelideus lemuroides), was almost totally insights come from long‐term studies that absent from fragments and regrowth forests document changes in communities. For example, along streams and its abundance in these large nocturnal marsupials were surveyed in habitats was only 0.02% of that in intact forest rainforest fragments in Queensland, Australia, in (Laurance et al. 2008). 1986–87 and again 20 years later in 2006–07 (Laurance et al. 2008). At the time of the first REFERENCES surveys, when fragments had been isolated for 20–50 years, the fauna differed markedly from Laurance, W. F., Laurance, S. G., and Hilbert, D. W. (2008). that in extensive rainforest. Over the subsequent Long‐term dynamics of a fragmented 20 years, even further changes occurred. rainforest mammal assemblage. Conservation Biology, Notably, the species richness in fragments had 22, 1154–1164.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 108. 1 HABITAT FRAGMENTATION AND LANDSCAPE CHANGE 93 required for a single individual or breeding unit, or for a self-sustaining population. Some species persist in fragmented landscapes by incorporating multiple fragments in their ter- ritory or daily foraging movements. In England, the tawny owl (Strix aluco) occupies territories of about 26 ha (hectares) in large deciduous woods, but individuals also persist in highly fragmented areas by including several small woods in their territory (Redpath 1995). There is a cost, however: individuals using multiple woods have lower breeding success and there is a higher turnover of territories between years. Species that require different kinds of habitats to meet regular needs (e.g. for foraging and breeding) can be greatly disadvantaged if these habitats become isolated. Individuals may then experience difficulty in moving between different parts of the landscape to obtain their required resources. Amphibians that move between a breeding pond and other habitat, such as overwintering sites in forest, are an example. Other attributes (in addition to fragment size) that influence the occurrence of species in- clude the type and quality of habitat, fragmentFigure 5.3 Variation in the spatial configuration of habitat in shape, land use adjacent to the fragment, andlandscapes with similar cover of native vegetation: a) subdivision (many the extent to which the wider landscape isolatesversus few patches); b) aggregated vs dispersed habitat; and c) compact populations. In the Iberian region of Spain, forvs complex shapes. All landscapes have 20% cover (shaded). example, the relative abundance of the Eurasian badger (Meles meles) in large forest fragments islandscapes need to know which species are mostvulnerable to these processes. 1.0 0.9 0.8 Frequency of occurrence5.3.1 Patterns of species occurrence 0.7in fragmented landscapes 0.6 0.5Many studies have described the occurrence of 0.4species in fragments of different sizes, shapes, 0.3composition, land-use and context in the land- 0.2scape. For species that primarily depend on 0.1fragmented habitat, particularly animals, frag- 0.0ment size is a key influence on the likelihood of 2–5 6–10 11–20 21–50 51–100 100occurrence (Figure 5.4). As fragment size de- Woodland area (ha)creases, the frequency of occurrence declines Figure 5.4 Frequency of occurrence of the common dormouseand the species may be absent from many (Muscardinus avellanarius) in ancient semi‐natural woods insmall fragments. Such absences may be because Herefordshire, England, in relation to increasing size‐class of woods.the fragment is smaller than the minimum area Data from Bright et al. (1994).© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 109. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLsignificantly influenced by habitat quality and consequence of habitat fragmentation, but ariseforest cover in the wider landscape (Virgos from land uses typically associated with subdivi-2001). In areas with less than 20% forest cover, sion. Populations may decline due to deaths ofbadger abundance in forests was most influenced individuals from the use of pesticides, insecti-by isolation (i.e. distance to a potential source cides or other chemicals; hunting by humans;area 10 000 ha), whereas in areas with 20–50% harvesting and removal of plants; and construc-cover, badgers were most influenced by the qual- tion of roads with ensuing road kills of animals.ity of habitat in the forest fragments. For example, in Amazonian forests, subsistence A key issue for conservation is the relative hunting by people compounds the effects of for-importance of habitat loss versus habitat frag- est fragmentation for large vertebrates such as thementation (Fahrig 2003). That is, what is the rela- lowland tapir (Tapir terrestris) and white-lippedtive importance of how much habitat remains in peccary (Tayassu pecari), and contributes to theirthe landscape versus how fragmented it is? Studies local extinction (Peres 2001).of forest birds in landscapes in Canada and Aus- Commonly, populations are also affected bytralia suggest that habitat loss and habitat frag- factors such as logging, grazing by domesticmentation are both significant influences, stock, or altered disturbance regimes that modifyalthough habitat loss generally is a stronger influ- the quality of habitats and affect populationence for a greater proportion of species (Trczinski growth. For example, in Kibale National Park, anet al. 1999; Radford and Bennett 2007). Important- isolated forest in Uganda, logging has resulted inly, species respond to landscape pattern in differ- long-term reduction in the density of groups of theent ways. In southern Australia, the main blue monkey (Cercopithecus mitza) in heavilyinfluence for the eastern yellow robin (Eopsaltria logged areas: in contrast, populations of blackaustralis) was the total amount of wooded cover and white colobus (Colobus guereza) are higher inin the landscape; for the grey shrike-thrush (Col- regrowth forests than in unlogged forest (Chap-luricincla harmonica) it was wooded cover togeth- man et al. 2000). Deterministic processes are partic-er with its configuration (favoring aggregated ularly important influences on the status of planthabitat); while for the musk lorikeet (Glossopsitta species in fragments (Hobbs and Yates 2003).concinna) the influential factor was not woodedcover, but the configuration of habitat and diver- Isolationsity of vegetation types (Radford and Bennett Isolation of populations is a fundamental conse-2007). quence of habitat fragmentation: it affects local populations by restricting immigration and emi- gration. Isolation is influenced not only by the5.3.2 Processes that affect species in fragmented distance between habitats but also by the effectslandscapes of human land-use on the ability of organisms toThe size of any population is determined by the move (or for seeds and spores to be dispersed)balance between four parameters: births, deaths, through the landscape. Highways, railway lines,immigration, and emigration. Population size is and water channels impose barriers to move-increased by births and immigration of indivi- ment, while extensive croplands or urban devel-duals, while deaths and emigration of individuals opment create hostile environments for manyreduce population size. In fragmented land- organisms to move through. Species differ inscapes, these population parameters are influ- sensitivity to isolation depending on their typeenced by several categories of processes. of movement, scale of movement, whether they are nocturnal or diurnal, and their response toDeterministic processes landscape change. Populations of one speciesMany factors that affect populations in fragmen- may be highly isolated, while in the same land-ted landscapes are relatively predictable in their scape individuals of another species can moveeffect. These factors are not necessarily a direct freely.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 110. 1 HABITAT FRAGMENTATION AND LANDSCAPE CHANGE 95 Isolation affects several types of movements, small initial population size. A decline in geneticincluding: (i) regular movements of individuals diversity may make a population more vulnerablebetween parts of the landscape to obtain to recessive lethal alleles or to changing environ-different requirements (food, shelter, breeding mental conditions.sites); (ii) seasonal or migratory movements ofspecies at regional, continental or inter-continen- · Fluctuations in the environment, such as varia- tion in rainfall and food sources, which affect birthtal scales; and (iii) dispersal movements (immi- and death rates in populations.gration, emigration) between fragments, whichmay supplement population numbers, increase · Small isolated populations are particularly vul- nerable to catastrophic events such as flood, fire,the exchange of genes, or assist recolonization if drought or hurricanes. A wildfire, for example,a local population has disappeared. In Western may eliminate a small local population whereas inAustralia, dispersal movements of the blue- extensive habitats some individuals survive andbreasted fairy-wren (Malurus pulcherrimus) are provide a source for recolonization.affected by the isolation of fragments (Brookerand Brooker 2002). There is greater mortality of 5.3.3 Metapopulations and the conservationindividuals during dispersal in poorly connected of subdivided populationsareas than in well-connected areas, with this dif-ference in survival during dispersal being a key Small populations are vulnerable to local extinc-factor determining the persistence of the species tion, but a species has a greater likelihood ofin local areas. persistence where there are a number of local For many organisms, detrimental effects of populations interconnected by occasional move-isolation are reduced, at least in part, by habitat ments of individuals among them. Such a setcomponents that enhance connectivity in the of subdivided populations is often termed a “me-landscape (Saunders and Hobbs 1991; Bennett tapopulation” (Hanski 1999). Two main kinds of1999). These include continuous “corridors” or metapopulation have been described (Figure 5.5).“stepping stones” of habitat that assist move- A mainland-island model is where a large main-ments (Haddad et al. 2003), or human land-uses land population (such as a conservation reserve)(such as coffee-plantations, scattered trees in pas- provides a source of emigrants that disperseture) that may be relatively benign environments to nearby small populations. The mainland pop-for many species (Daily et al. 2003). In tropical ulation has a low likelihood of extinction, where-regions, one of the strongest influences on the as the small populations become extinct relativelypersistence of species in forest fragments is their frequently. Emigration from the mainlandability to live in, or move through, modified supplements the small populations, introduces“countryside” habitats (Gascon et al. 1999; Seker- new genetic material and allows recolonizationcioglu et al. 2002). should local extinction occur. A second kind of metapopulation is where the set of interacting populations are relatively similar in size and allStochastic processes have a likelihood of experiencing extinction (Fig-When populations become small and isolated, ure 5.5b). Although colonization and extinctionthey become vulnerable to a number of stochastic may occur regularly, the overall population per-(or chance) processes that may pose little threat to sists through time.larger populations. Stochastic processes include The silver-spotted skipper (Hesperia comma), athe following. rare butterfly in the UK, appears to function as· Stochastic variation in demographic parameterssuch as birth rate, death rate and the sex ratio of a metapopulation (Hill et al. 1996). In 1982, but- terflies occupied 48 of 69 patches of suitableoffspring. grassland on the North Downs, Surrey. Over the· Loss of genetic variation, which may occur due toinbreeding, genetic drift, or a founder effect from a next 9 years, 12 patches were colonized and seven populations went extinct. Those more susceptible© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 111. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLFigure 5.5 Diagrammatic representation of two main types of metapopulation models: a) a mainland‐island metapopulation and b) metapopulationwith similar‐sized populations. Habitats occupied by a species are shaded, unoccupied habitat fragments are clear, and the arrows indicate typicalmovements. Reprinted from Bennett (1999).to extinction were small isolated populations, 5.4 Effects of landscape changewhereas the patches more likely to be colonized on communitieswere relatively large and close to other largeoccupied patches. 5.4.1 Patterns of community structure The conservation management of patchily- in fragmented landscapesdistributed species is likely to be more effective by For many taxa—birds, butterflies, rodents, rep-taking a metapopulation approach than by focus- tiles, vascular plants, and more—species richnessing on individual populations. However, “real in habitat fragments is positively correlated withworld” populations differ from theoretical models. fragment size. This is widely known as theFactors such as the quality of habitat patches and species-area relationship (Figure 5.6a). Thus,the nature of the land mosaic through which move- when habitats are fragmented into smaller pieces,ments occur are seldom considered in theoretical species are lost; and the likely extent of this lossmodels, which emphasize spatial attributes (patch can be predicted from the species-area relation-area, isolation). For example, in a metapopulation ship. Further, species richness in a fragment typi-of the Bay checkerspot butterfly (Euphydryas editha cally is less than in an area of similar size withinbayensis) in California, USA, populations in topo- continuous habitat, evidence that the fragmenta-graphically heterogeneous fragments were less tion process itself is a cause of local extinction.likely to go extinct than those that were in topo- However, the species-area relationship does notgraphically uniform ones. The heterogeneity reveal which particular species will be lost.provided some areas of suitable topoclimate each Three explanations given for the species-areayear over a wide range of local climates (Ehrlich relationship (Connor and McCoy 1979) are thatand Hanski 2004). small areas: (i) have a lower diversity of habitats; There also is much variation in the structure (ii) support smaller population sizes and thereforeof subdivided populations depending on the fewer species can maintain viable populations;frequency of movements between them. At and (iii) represent a smaller sample of the originalone end of a gradient is a dysfunctional meta- habitat and so by chance are likely to have fewerpopulation where little or no movement oc- species than a larger sample. While it is difficult tocurs; while at the other extreme, movements distinguish between these mechanisms, the mes-are so frequent that it is essentially a single sage is clear: when habitats are fragmented intopatchy population. smaller pieces, species are lost.© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 112. 1 HABITAT FRAGMENTATION AND LANDSCAPE CHANGE 97 50 specialized ecological requirements are those lost from communities in fragments. In several 40 tropical regions, birds that follow trails of army ants and feed on insects flushed by the ants in-Number of species 30 clude specialized ant-following species and others that forage opportunistically in this way. In rainforest in Kenya, comparisons of flocks of 20 ant-following birds between a main forest and forest fragments revealed marked differences 10 (Peters et al. 2008). The species richness and num- ber of individuals in ant-following flocks were 0 0 10 20 30 40 50 60 lower in fragments, and the composition of flocks Area (ha) more variable in small fragments and degraded forest, than in the main forest. This was a conse- 60 quence of a strong decline in abundance of five species of specialized ant-followers in fragments, 50 whereas the many opportunistic followers (51 species) were little affected by fragmentationNumber of species 40 (Peters et al. 2008). 30 The way in which fragments are managed is a particularly important influence on the composi- 20 tion of plant communities. In eastern Australia, for example, grassy woodlands dominated by 10 white box (Eucalyptus albens) formerly covered 0 several million hectares, but now occur as small 0 10 20 30 40 50 60 fragments surrounded by cropland or agricultur- Tree cover (%) al pastures. The species richness of native under-Figure 5.6 Species‐area relationships for forest birds: a) in forest story plants increases with fragment size, asfragments of different sizes in eastern Victoria, Australia (data from Loyn expected, but tree clearing and grazing by domes-1997); b) in 24 landscapes (each 100 km2) with differing extent of tic stock are also strong influences (Prober andremnant wooded vegetation, in central Victoria, Australia (data fromRadford et al. 2005). The piecewise regression highlights a threshold Thiele 1995). The history of stock grazing has theresponse of species richness to total extent of wooded cover. strongest influence on the floristic composition in woodland fragments: grazed sites have a greater invasion by weeds and a more depauperate na- Factors other than area, such as the spatial and tive flora.temporal isolation of fragments, land management The composition of animal communities inor habitat quality may also be significant predic- fragments commonly shows systematic changestors of the richness of communities in fragments. in relation to fragment size. Species-poor commu-In Tanzania, for example, the number of forest- nities in small fragments usually support a subsetunderstory bird species in forest fragments (from of the species present in larger, richer fragments0.1 to 30 ha in size) was strongly related to frag- (Table 5.1). That is, there is a relatively predict-ment size, as predicted by the species-area rela- able change in composition with speciestionship (Newmark 1991). After taking fragment “dropping out” in an ordered sequence in succes-size into account, further variation in species rich- sively smaller fragments (Patterson and Atmarness was explained by the isolation distance of 1986). Typically, rare and less common specieseach fragment from a large source area of forest. occur in larger fragments, whereas those present Species show differential vulnerability to in smaller fragments are mainly widespread andfragmentation. Frequently, species with more- common. This kind of “nested subset” pattern© Oxford University Press 2010. All rights reserved. For permissions please email:
  • 113. Sodhi and Ehrlich: Conservation Biology for All. CONSERVATION BIOLOGY FOR ALLTable 5.1 A diagrammatic example of a nested subset pattern of of communities. The loss of a species or a changedistribution of species (A–J) within habitat fragments (1–9). in its abundance, particularly for species that in-Species Fragments teract with many others, can have a marked effect on ecological processes throughout fragmented 1 2 3 4 5 6 7 8 9 landscapes. A + + + + + + + + Changes to predator-prey relationships, for ex- B + + + + + + + C + + + + + + + ample, have been revealed by studies of the level of D + + + + + + predation on birds’ nests in fragmented landscapes E + + + + + + (Wilcove 1985). An increase in the amount of forest F + + edge, a direct consequence of fragmentation, in- G + + + creases the opportunity for generalist predators H + + I + + + associated with edges or modified land-uses to J + prey on birds that nest in forest fragments. In Swe- den, elevated levels of nest predation (on artificial eggs in experimental nests) were recorded in agri- cultural land and at forest edges compared withhas been widely observed: for example, in butter- the interior of forests (Andrén and Angelstamfly communities in fragments of lowland rainfor- 1988). Approximately 45% of nests at the forestest in Borneo (Benedick et al. 2006). edge were preyed upon compared with less than At the landscape level, species richness has fre- 10% at distances 200 m into the forest. At thequently been correlated with heterogeneity in the landscape scale, nest predation occurred at a great-landscape. This relationship is particularly rele- er rate in agricultural and fragmented forest land-vant in regions, such as Europe, where human scapes than in largely forested landscapes (Andrénland-use has contributed to cultural habitats that 1992). The relative abundance of different corvidcomplement fragmented natural or semi-natural species, the main nest predators, varied in relationhabitats. In the Madrid region of Spain, the overall to landscape composition. The hooded crowrichness of assemblages of birds, amphibians, rep- (Corvus corone cornix) occurred in greatest abun-tiles and butterflies in 100 km2 landscapes is dance in heavily cleared landscapes and was pri-strongly correlated with the number of different marily responsible for the greater predationland-uses in the landscape (Atauri and De Lucio pressure recorded at forest edges.2001). However, where the focus is on the com- Many mutualisms involve interactions be-munity associated with a particular habitat type tween plants and animals, such as occurs in the(e.g. rainforest butterflies) rather than the entire pollination of flowering plants by invertebrates,assemblage of that taxon, the strongest influence birds or mammals. A change in the occurrence oron richness is the total amount of habitat in the abundance of animal vectors, as a consequence oflandscape. For example, the richness of woodland- fragmentation, can disrupt this process. For manydependent birds in fragmented landscapes in plant species, habitat fragmentation has a nega-southern Australia was most strongly influenced