Trophic downgrading of planet earth


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Discussion of Estes et al. 2011 by Abelardo Colon Nieves, CIAM 6117, UPR Río Piedras

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Trophic downgrading of planet earth

  1. 1. Trophic Downgrading of Planet Earth Estes et al. 2011. Science. 333:301-306 Abelardo Colon Nieves Coastal Environment 11/13/13 1
  2. 2. Index • • • • Background Keywords and concepts Paper discussion Conclusion 11/13/13 2
  3. 3. James A. Estes • • • Project: Population Dynamics and Biology of the California Sea Otter at the Southern End of its Range Education: B.A. Zoology, University of Minnesota 1967 M.S. Zoology, Washington State University 1969 Ph.D. Biological Sciences/Statistics, University of Arizona 1974 Positions: - 1984-present Supervisory Zoologist, GM-486/15, California Science Center, National Biological Service, Santa Cruz, California - 1978-pressent Adjunct Professor, Biological Sciences, University of California, Santa Cruz - 1979-present Research Biologist, Institute for Marine Sciences, University of California, Santa Cruz - 1978-1981 Wildlife Biologist (Research), GS-486/12, Marine Mammal Section, National Fish and Wildlife Laboratory, FWS, Santa Cruz, California - 1977-1978 Wildlife Biologist (Research), GS-486/12, Marine Mammal Section, National Fish and Wildlife Laboratory, FWS, Anchorage, Alaska - 1974-1977 Wildlife Biologist (Research), GS-486/11, Marine Mammal Section, National Fish and Wildlife Laboratory, FWS, Anchorage, Alaska 11/13/13 3
  4. 4. Index • • • • Background Keywords and concepts Paper discussion Conclusion 11/13/13 4
  5. 5. Keywords and concepts 11/13/13 5
  6. 6. Mass Extinction Events 11/13/13 6
  7. 7. 6th massive extinction event (current): Homo sappiens loss of larger-bodied animals in general and of apex consumers in particular 11/13/13 7
  8. 8. Apex predator Predators with few to no predators of their own, residing at the top of their food chain. Apex consumers species occupy the highest trophic level and have a crucial role in maintaining the health of their ecosystems. 11/13/13 8
  9. 9. Marine Food Web/chain 11/13/13 9
  10. 10. Think??? -Human intervention to nature, to what extend is environmentally safe? -Indirect and direct environmental implications in human disturbed ecosystem… -It is reversible? How long would it take to reach equilibrium? -Global perspective… 11/13/13 10
  11. 11. Index • • • • Background Keywords and concepts Paper discussion Conclusion 11/13/13 11
  12. 12. Trophic Downgrading of Planet Earth • Tropic downgrading is defined as the studying concept of consequences by removing large apex consumers from nature. • Link between loss of apex consumers and effects disease, fire, carbon sequestration, invasive species and biochemical dynamics in earth’s soil, water and atmosphere. 11/13/13 12
  13. 13. Ecological Theory 3 main ideas: 1) An ecosystem may be shaped by apex Consumers. “trophic cascades,” broadly defined as the propagation of impacts by consumers on their prey downward through food webs. 11/13/13 13
  14. 14. Ecological Theory 2) Alternative stable. Alternative stable states occur when perturbations of sufficient magnitude and direction push ecosystems from one basin of attraction to another. Tipping points (also known as thresholds or breakpoints), around which abrupt changes in ecosystem structure and function occur, often characterize transitions between alternative stable states. Ecosystem phase shifts can also display hysteresis, a phenomenon in which the locations of tipping points between states differ with the directionality of change. 11/13/13 14
  15. 15. Ecological Theory 3) Connectivity. Connectivity holds that ecosystems are built around interaction webs within which every species potentially can influence many other species. These interactions, which include both biological processes (predation, competition, and mutualism) and physicochemical processes (the nourishing or limiting influences of water, temperature, and nutrients), link species together at an array of spatial scales in a highly complex network. 11/13/13 15
  16. 16. These 3 main keys set the stage for the idea of trophic downgrading. 11/13/13 16
  17. 17. Apex consumer absent 11/13/13 present Coral reef ecosystems Uninhabited Jarvis Island (right, unfished) and neighboring Kiritimati Island (left, with an active reef fishery). Fishing alters the patterns of predation and herbivory, leading to shifted benthic dynamics, with the competitive advantage of reef-building corals and coralline algae diminished in concert with removal of large fish. 17
  18. 18. Cryptic Nature of Tropic Downgrading • Not easy to prove under equilibrium conditions but if it is perturbed, responses to the loss or addition of species could take several years or decades. • Population of apex consumers have long been reduced during time passes. • Scale of tropic downgrading is too large in comparison to empirical studies of species interactions that have been done on small or weakly motile species. 11/13/13 18
  19. 19. Think??? • Tropic downgrading is happening for real or not? • Tell me prove of that. 11/13/13 19
  20. 20. The widespread Occurrence of Tropic Cascades • Top-down forcing and trophic cascades often have striking effects on the abundance and species composition of autotrophs, leading to regime shifts and alternative states of ecosystems. 11/13/13 20
  21. 21. Sea Otter 11/13/13 21
  22. 22. Indirect effects of losing apex consumers • Disease: The establishment of no-take marine reserves in the Channel Islands of southern California led to increases in the size and abundance of spiny lobsters (Panulirus interruptus) and declines in population densities of sea urchins, which are preyed on by the lobsters. The reduced urchin densities thwarted the spread of disease among individual sea urchins, which led to a lowered frequency of epidemics of sea urchin wasting disease within the reserves. 11/13/13 22
  23. 23. Marine disease • In freshwater systems, the localized rise and fall of human malaria is associated with the impacts of predatory fishes on planktivores, which are in turn important consumers of mosquito larvae. 11/13/13 23
  24. 24. Physical and chemical influences • Trophic cascades associated with the presence or absence of apex predatory fishes in lakes can affect phytoplankton density, in turn affecting the rate of primary production, the uptake rate of CO2, and the direction of carbon flux between lakes and the atmosphere. Where apex predatory fishes are present in sufficient numbers, they reduce the abundance of smaller planktivorous minnows, thus releasing zooplankton from limitation by planktivores and increasing consumption rates of phytoplankton by zooplankton. This trophic cascade causes lakes to switch from net sinks for atmospheric CO2 when predatory fishes are absent to net sources of atmospheric CO2 when these fishes are present. 11/13/13 24
  25. 25. The whale industry example • Industrial whaling during the 20th century transferred some 105 million tons of carbon from great whales to the atmosphere, and even today whale feces return various limiting nutrients from the aphotic to photic zones, thereby directly enhancing primary productivity and its influence on carbon flux and sequestration. 11/13/13 25
  26. 26. Water: Salmon example • In rivers, mass spawning by salmon suspends sediments, thus increasing downstream sediment transport. This flushing of stream bed sediments by the spawning fish and the increased circulation of freshwater through the gravel interstices of the stream bed have positive feedbacks on salmon populations by increasing oxygen for incubating eggs and fry and decreasing the frequency with which bedmobilizing floods kill salmon in these early life stages. 11/13/13 26
  27. 27. Invasive species • Invasive species. A common feature of many successful invasive species is that they have left behind their natural predators and freed themselves from top-down control. Likewise, the loss of native predators leaves ecosystems more vulnerable to invasion by nonnative species. 11/13/13 27
  28. 28. Lion Fish sightings in Puerto Rico 11/13/13 28
  29. 29. Index • • • • Background Keywords and concepts Paper discussion Conclusion 11/13/13 29
  30. 30. Conclusion • These examples support the conclusion that disruptions of trophic cascades due to the decline of predation constitute a threat to biodiversity from within for which the best management solution is likely the restoration of effective predation regimes. 11/13/13 30
  31. 31. A Paradigm Shift in Ecology • Before: apex consumer seen as ecological passengers riding at the top of the trophic pyramid but having little impact on the structure below. • After: Bottom-up forces are ubiquitous and fundamental, and they are necessary to account for the responses of ecosystems to perturbations, but they are not sufficient. Topdown forcing must be included in conceptual overviews if there is to be any real hope of understanding and managing the workings of nature. 11/13/13 31
  32. 32. Think Coastal Environment… • Paper discussion that can we link with this review research? • • Ecological extinction and evolution in brave new ocean- Jackson 2008 The value of estuarine and coastal ecosystem services- Barbier et al. 2011 (services, goods and cultural benefits…) 11/13/13 32
  33. 33. Thank You 11/13/13 33