环境生态学Chapter 7

环境生态学环境生态学Chapter 7Chapter 7 Conserving BiologicalResources7.1 Value of Wild Species7.2 Biodiversity7.1 Value of Wild Species7.1.1 Biological Wealth About 1.75 million species of plants,animals,and microbes have been examined,named,and classified,but scientists estimate that between 4 million and 112 million additional species have not yet been systematically explored.7.1.2 Two Kinds of Value instrumental value:its existence or use benefits some other entityintrinsic value:it has value for its own sake The value of natural species Sources for agriculture,forestry,aquaculture,and animal husbandrySources for medicines,pharmaceuticalsRecreational,aesthetic,and scientific valueIntrinsic value7.2 Biodiversity7.2.1 ConceptBiodiversity:the variety and variability among living organisms and the ecological complexes in which they occurSpecies diversity:the number of species that occur in an area The number of species is counted in a gradually enlarged area of sampling,the result is a curve.The number of species rises rapidly at first,but it slows as the area of sampling increases because the same species are encountered again and again.7.2.2 The species-area curve:Figure 7.1 Preserving 50%of total habitat area often leaves about 90%of the original species remaining alive 7.2.3 Extinction Species extinction:Ecological extinction:a species has become so rare that it has essentially no role or impact on its ecosystem a species has died out in a local areaChange physical environment:1.Habitat disruptionExamplesDrain swamp,toxic pollutionChange biological environment:2.Introduce new species3.Overhunting4.Secondary extinctionsNew predatorBiggame huntingLoss of food speciesTable 7.3 Four ways that humans cause population decline and species extinctionOne is that small populations may have breeding problems.The second cause is that small populations are much more easily wiped out by random environmental fluctuationsTwo basic causes for this extinction vortexThe smallest population size needed to stay above the extinction vortex is often called the minimum viable population(MVP)7.2.4 Reasons for Decline of BiodiversityPhysical Alteration of HabitatsThe Population Factor Exotic Species Overuse Adopt specific national biodiversity action plans and strategiesEstablish a system of protected areas and ecosystems within the countryEstablish policies that provide incentives to promote sustainable use of biological resources 7.2.5 Convention on Biological Diversity(1992 in Rio de Janeiro)Restore habitats that have been degraded.Protect threatened species.Respect and preserve knowledge and practices of indigenous peoples.Respect the ownership of genetic resources by countries,and share the technologies developed from those resources.