Lecture 11 biodiversity


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Lecture 11 biodiversity

  1. 1. Environmental ScienceA Study of Interrelationships Eleventh Edition Enger & Smith Chapter 11 Biodiversity IssuesCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  2. 2. Biodiversity Issues
  3. 3. Outline Biodiversity Loss and Extinction Describing Biodiversity The Value of Biodiversity Threats to Biodiversity What Is Being Done to Preserve Biodiversity?
  4. 4. Biodiversity Loss and Extinction Biodiversity is a broad term used to describe the diversity of genes, species, and ecosystems in a region. Extinction is the elimination of all the individuals of a particular species. • Extinction is a natural and common event in the history of biological evolution. • It, and the resulting loss of biodiversity, is also a major consequence of human domination of the Earth.
  5. 5. Biodiversity Loss and Extinction Local extinctions, although relatively common, indicate the future of a species is not encouraging. As population is reduced in size, some of the genetic diversity is likely to be lost. Certain kinds of species are more likely to go extinct than others: • Species with small, dispersed populations – Successful breeding is difficult.
  6. 6. Biodiversity Loss and Extinction• Organisms in small, restricted areas, such as islands. – Environmental changes have large effect.• Specialized organisms – Relying on constancy of a few key factors.• Organisms at higher trophic levels. – Low population sizes and reproductive rates.
  7. 7. Biodiversity Loss and Extinction
  8. 8. Biodiversity Loss and Extinction As human populations grew, and their tools became more advanced, the impact a single human could have on surroundings increased. Environmental modifications allowed larger, dense human populations to survive, but at the expense of previously existing ecosystems. Nearly all Earth’s surface has been affected in some way by human activity.
  9. 9. Describing Biodiversity Genetic diversity is a term used to describe the number of kinds of genes present in a population. • High genetic diversity indicates many different kinds of genes present in individuals of a population. • Low genetic diversity indicates nearly all individuals share the same genes and therefore the same characteristics.
  10. 10. Describing Biodiversity Several things influence a population’s genetic diversity: • Mutations introduce new genetic information into a population by modifying current genes. • Migration allows movement of genes from one population to another. • Sexual reproduction generates new genetic combinations.
  11. 11. Describing Biodiversity• Population size is an important factor: The smaller the population, the less genetic diversity it can contain. – There are fewer variations for each characteristic. – Random events can significantly alter the genetic diversity in small populations.• Selective breeding can affect diversity because undesirable characteristics are eliminated. – Many domesticated plants and animals could not survive without human help.
  12. 12. Describing Biodiversity Species diversity is a measure of the number of different species present in an area. • Species richness refers to the number of different kinds of species in an area. • Taxonomic richness takes into account the number of different taxonomic categories of the species present.
  13. 13. Describing Biodiversity When humans exploit an area, they influence species diversity. • They convert natural ecosystems to human-managed ecosystems. – They harvest certain species for their use. – They specifically eliminate species that compete with desirable species. – They introduce nonnative species to an area.
  14. 14. Describing Biodiversity Estimates of the actual number of species range from a few million to 100 million. • About 1.4 million species have been described. – Many species are naturally rare, and others live in areas difficult to reach.
  15. 15. Describing Biodiversity Ecosystem diversity is a measure of the number of kinds of ecosystems present in an area. Many regions of the world appear to be quite uniform in terms of the kinds of ecosystems present. • For example, many parts of the world are deserts: – While there are general similarities, each is different and has specific organisms typical to the region. – Local topographic conditions create unique patches of landscape.
  16. 16. The Value of Biodiversity Biological and Ecosystem Services Values • Humans rely on organic molecules produced by other organisms for food. • Each organism is involved in a vast network of relationships with other organisms. • Accidental extinction of one of these species could be devastating to the ecosystem and the humans who use it. – Vegetation holds soil together and protects watersheds. – Plants remove carbon dioxide from the atmosphere. – Decomposers recycle organic wastes.
  17. 17. The Value of Biodiversity Choices between competing uses for ecosystems are often determined by economic values. • Value can be assigned to services provided by intact, functioning ecosystems. – Current estimate of $33 trillion per year, but that figure may be low. • Some resources are difficult to assign specific monetary value: – Wildlife (consumed by those who harvest it) – Medicinal plants
  18. 18. The Value of Biodiversity A case can be made that all species have an intrinsic value and a fundamental right to exist. • Extinction is not necessarily bad, but human-initiated extinction is. • Experiencing natural landscapes and processes is an important human right.
  19. 19. The Value of Biodiversity The values held by a person are typically shaped by experience. • As the shift from rural to urban continues, there is continual erosion of natural experiences that can shape the values of people. • These values are important in determining how society will approach threats to biodiversity.
  20. 20. Threats to Biodiversity Four major human activities threaten to reduce biodiversity. • Habitat loss • Overexploitation • Introduction of exotic species • Persecution of pest organisms
  21. 21. Threats to BiodiversityCauses of extinction
  22. 22. Threats to Biodiversity The World Conservation Union estimates that 80%- 90% of threatened species are under threat as a result of habitat loss or fragmentation. Habitat loss and fragmentation are thought to be a major cause of past extinctions.
  23. 23. A quarter of worlds mammals face extinction, survey findsBy Kenneth R. WeissLos Angeles TimesArticle Launched: 10/06/2008 06:56:38 PM PDTBARCELONA, Spain — At least one-quarter of the worlds mammals in the wild are threatened with extinction,according to a survey released Monday that blames the loss of wildlife habitat, hunting and poaching for the steepdeclines.The survey, assembled over five years by 1,700 researchers in 130 countries, is the most comprehensive yet toassess the status and future of mammals on every continent and in every ocean.The "baiji," or Chinese river dolphin, faces extinction and already might have joined the species that have vanishedfrom Earth.Others are not far behind, such as the "vaquita," a small porpoise that is drowning in fishing nets in the northernGulf of California; the North Atlantic right whale; and various monkeys and other primates hunted by poachers inAfrica.Scientists have determined that about one-quarter of the worlds 5,487 species of mammals are threatened withextinction. The proportion of marine mammals at risk appears to be higher, with an estimated one-third facing aserious threat. Many are killed when they are struck by ships or entangled in fishing gear.About one-half of the worlds remaining apes, monkeys and other primates face threats from hunting or destructionof forests to make way for farming, said Russell A. Mittermeier, president of Conservation International.Scientists find mammal extinction worrisome because a diversity of species stabilizes the planet. Each extinctionAdvertisementdisrupts this balance and ripples through the food chain, making it difficult for other species, including humans, tosurvive.The bleak assessment was released in Barcelona at the World Conservation Congress, a meeting of 8,000scientists, conservationists, business leaders and representatives from governmental environmental ministries.
  24. 24. Threats to Biodiversity About 40% of the world’s land surface has been converted to cropland and permanent pasture. Typically, the most productive natural ecosystems (forests and grasslands) are the first to be modified by humans. Pressures to modify the environment are greatest in areas with high population density.
  25. 25. Threats to Biodiversity Originally, half of the U.S., three-fourths of Canada, and almost all of Europe, and significant portions of the rest of the world were forested. Deforestation is the process of destroying a forest, often for the purposes of fuel, building materials, or to clear land for farming.
  26. 26. Threats to Biodiversity Modern forest management practices involve a compromise that allows economic exploitation while maintaining some environmental values of the forest. • Forested areas effectively: – Reduce erosion. – Reduce runoff. – Modify the climate. – Provide recreational opportunities.
  27. 27. Threats to BiodiversityChanges in forest area
  28. 28. Threats to Biodiversity Clear cutting is the removal of all trees in an area. It is economical but increases erosion, especially on steep slopes. Patchwork clear cutting is clear cutting in small, unconnected patches; preserves biodiversity. Selective harvesting is single species tree harvesting. It is not as economical, but reduces ecosystem damage.
  29. 29. Threats to BiodiversityClear cutting
  30. 30. Threats to Biodiversity Tropical forests have greater species diversity than any other ecosystem. They are not as likely as temperate forests to regenerate after logging due to poor soil characteristics. Currently, few tropical forests are being managed for long-term productivity.
  31. 31. Threats to Biodiversity Several concerns are raised by tropical deforestation: • It significantly reduces species diversity in the world. • It impacts the climate via lowered transpiration. • Deforested lands are easily eroded. • Without the forests to trap CO2, there may be increased global warming. • Human population pressure is greatest in tropics, and still increasing.
  32. 32. Threats to Biodiversity Many lumber companies maintain forest plantations as crops and manage them in the same way farmers manage crops. • Plant single species, even-aged forests of fast growing hybrid trees. • Competing species are controlled by fire, and insects controlled by spraying. • Trees mature to harvestable size in as low as 20 years (vs. 100). – Quality of lumber reduced. – Low species diversity and wildlife value.
  33. 33. Threats to Biodiversity Rangelands are lands too dry to support crops, but receive enough precipitation to support grasses and drought-resistant shrubs. They are often used to raise low-density populations of domesticated or semi- domesticated animals. Wildlife are usually introduced species not native to the region.
  34. 34. Threats to BiodiversityUse of rangelands
  35. 35. Threats to Biodiversity The conversion of rangelands to grazing by domesticated animals has major impacts on biodiversity. • Selective eating habits of livestock tend to reduce certain species of native plants and encourage others. • Important to regulate number of livestock on rangelands, especially in dry areas. – Overgrazing is a severe problem where human population pressures are great. – Desertification is the process of converting arid or semiarid land to desert because of improper human use.
  36. 36. Threats to BiodiversityDesertification
  37. 37. Threats to Biodiversity In marine ecosystems, much of the harvest is restricted to shallow parts of the ocean where bottom-dwelling fish can be easily harvested. Trawls are nets dragged along the bottom. • They disturb the seafloor and cause habitat damage. About 25% of catch is undesirable, and thus discarded, but they are usually dead, and their removal further alters the ecological nature of the seafloor.
  38. 38. Habitat Loss in Aquatic Ecosystems Freshwater systems are often modified for navigation, irrigation, flood control, or power production. All of these processes may alter natural ecosystems and change numbers or kinds of aquatic organisms present.
  39. 39. Threats to BiodiversityChanges in world marine fish harvests 1950-1995
  40. 40. Threats to Biodiversity About 4.3% of U.S. land is developed as urban centers, industrial sites, and transportation infrastructure. • Many areas are covered with impermeable surfaces that prevent plant growth and divert rainfall. • It is difficult to generalize about the impact of urban centers on a worldwide basis. • The trend is toward greater urbanization.
  41. 41. Threats to Biodiversity According to the World Conservation Union, overexploitation is responsible for over 30% of endangered animal species and 8% of endangered plant species. The World Wildlife Fund estimates illegal trade in wild animals globally produces $2–$30.5 billion annually. • These activities have already resulted in local extinctions.
  42. 42. Threats to Biodiversity U.N. estimates 70% of world’s marine fisheries are overexploited or are fully exploited and in danger of being overexploited. • Amount of fish caught has remained relatively constant since 1989. • The commercial fishing industry has been attempting to market species previously regarded as unacceptable.
  43. 43. Threats to Biodiversity Fish farming (aquaculture) is becoming increasingly important as a source of fish production. Currently, about 60% of all aquaculture production is from freshwater systems. The environmental impacts are similar to those of marine systems: • Nutrient overloads • Escape into natural waters • Land conversion
  44. 44. Threats to Biodiversity Meat from wild animals is often referred to as bush meat. The Wildlife Conservation Society estimates 70% of wildlife species in Asia and Africa and about 40% of species in Latin America are being hunted unsustainably. • Hunting of wildlife is a part of all subsistence cultures. • Many kinds of wildlife are considered delicacies and are highly prized for the home and restaurant trade.
  45. 45. Threats to Biodiversity Harvest of living animals for the pet and aquarium trade is a significant problem. • The method of capture is often problematic. – Destruction of bird nests. – Toxins used to stun fish. Wildlife are also hunted because parts of the animal may have particular value. – Ivory and animal skins – Traditional medicines
  46. 46. Threats to Biodiversity Some introductions of exotic species are purposeful, while others are accidental. The World Conservation Union estimates about 30% of birds and 15% of plants are threatened because they are unable to successfully compete against invasive exotic species.
  47. 47. Threats to Biodiversity Introduction of disease has had considerable impact on American forests. • Chestnut blight • Dutch elm disease Various insects have had an effect on ecosystem structure. • Asian longhorned beetle Freshwater ecosystems have been greatly affected. • Zebra mussel
  48. 48. Threats to BiodiversityThe Asian longhorned beetle
  49. 49. Threats to Biodiversity Systematic killing of certain organisms that interfere with human activities also results in reduced biodiversity. • Large predators have been locally exterminated because they preyed on domestic animals. • Passenger pigeons became extinct primarily because of increased conversion of forested land.
  50. 50. Threats to Biodiversity Predator and competitor control activities are still used in some special situations. • It is generally not considered to be cost-effective in most cases. – Hunting and trapping of wolves in Alaska and Canada is an exception. – Control of cowbird populations has been used to enhance breeding success of Kirtland’s warblers.
  51. 51. What Is Being Done to Preserve Biodiversity? The World Conservation Union (IUCN) estimates by the year 2010, at least 500,000 species of plants and animals may have been exterminated. • IUCN classifies species in danger of extinction into four categories: – Endangered – Vulnerable – Rare – Indeterminate
  52. 52. What Is Being Done to Preserve Biodiversity? Awareness and concern about loss of biodiversity are high in many developed countries. Most vulnerable species in these areas have already been eliminated. Loss of biodiversity is not a high priority for the general public in developing countries. They are more concerned with immediate needs of food and shelter than long-range issues such as species extinction.
  53. 53. What Is Being Done to Preserve Biodiversity? In the U.S., the primary action related to the preservation of biodiversity involved the passage of the Endangered Species Act (1973). This legislation designates species as endangered or threatened and gives the U.S. government jurisdiction over those species. • Directs that no activity by a government agency should lead to the extinction of an endangered species. • Directs government agencies to use whatever means necessary to preserve the species in question.
  54. 54. What Is Being Done to Preserve Biodiversity? Endangered species are those that have such small numbers that they are in immediate danger of becoming extinct. Threatened species could become extinct if a critical environmental factor is changed. • The preservation question ultimately becomes one of assigning value to the species. • Amendments to ESA have weakened ability of U.S. government to add new species to the list.
  55. 55. What Is Being Done to Preserve Biodiversity? The designation of certain areas as wilderness is a sensitive issue. The Wilderness Act (1964) defines wilderness as “an area where the Earth and its community of life are untrammeled by man, where man himself is a visitor who does not remain.”
  56. 56. What Is Being Done to Preserve Biodiversity? Habitat Analysis and Management • Animals have highly specific habitat requirements that change throughout the year. • Steps can be taken to alter habitat and improve species success. • Modifications made to enhance the success of a species are known as habitat management.
  57. 57. What Is Being Done to Preserve Biodiversity? Game species are often managed so they do not exceed carrying capacity of their habitat. Wildlife managers use population censuses to check if populations are within appropriate levels. With suitable habitat and protection, most wild animals can maintain a sizeable population. High reproductive capacities and heavy protection have caused very large populations to arise from once-rare animals.
  58. 58. What Is Being Done to Preserve Biodiversity? Wildlife management often involves harvesting for sport and meat. • Regulating hunting activity is an important population management technique. • Seasons usually occur in the fall so surplus animals are taken before the challenges of winter. When populations get too small, artificial introductions can be implemented. • Native species can be reintroduced to areas where they had been extinct. • Non-native species are introduced for empty niches.
  59. 59. What Is Being Done to Preserve Biodiversity?Managing a wildlife population
  60. 60. What Is Being Done to Preserve Biodiversity? Migratory birds can travel thousands of kilometers. • They travel north in spring to reproduce. • They travel south in fall to escape cold temperatures. International agreements may be necessary to maintain appropriate habitat.
  61. 61. What Is Being Done to Preserve Biodiversity?Migration routes for North American waterfowl
  62. 62. What Is Being Done to Preserve Biodiversity? Coastal regions are most productive regions of the oceans. • Sunlight penetration of shallow water makes it warm. • Nutrient deposition from land makes this region fertile. • Wind/wave action stirs nutrients. Fishing pressure is concentrated here. One of the major problems associated with the management of marine fisheries is achieving agreement on harvest limits.
  63. 63. What Is Being Done to Preserve Biodiversity? Humans have easy access to freshwater ecosystems, so management of these systems is much more intense. They are typically easier to regulate because of containment within a smaller political region. Many N. American freshwater fisheries are primarily managed for sport fishery. Fisheries biologists pay special attention to water quality.
  64. 64. Summary Loss of biodiversity has become a major concern. Ecosystems involve the interactions of organisms and their physical environment. The loss of key species can result in the loss of a type of ecosystem either locally or worldwide. Functioning ecosystems and their component organisms provide many valuable services that are often overlooked because they are not easily measured in economic terms.
  65. 65. Summary Many people also consider the loss of biodiversity to be an ethical problem. The primary causes of habitat loss are by: • Humans converting ecosystems to agriculture and grazing • Overexploitation by harvesting species at unsustainable levels • Introduction of exotic species that disrupt ecosystems and compete or prey on native organisms • Purposeful killing of pest organisms such as large predators.
  66. 66. Summary Protection of biodiversity typically involves legal protections by national laws and international agreements, and management of the use of species and ecosystems at sustainable levels.