rav65819_ch59_1237-1260

rav65819_ch59_1237-1260 - ; 59 chapter introduction...

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;;;;;;;;;; 59 chapter introduction Conservation Biology
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AMONG THE GREATEST CHALLENGES facing the biosphere is the accelerating pace of species extinctions. Not since the end of the Cretaceous period 65 million years ago have so many species become extinct in so short a time span. This challenge has led to the emergence of the discipline of conservation biology. Conservation biology is an applied science that seeks to learn how to preserve species, communities, and ecosystems. It studies the causes of declines in species richness and attempts to develop methods for preventing such declines. In this chapter, we first examine the biodiversity crisis and its importance. Then, using case histories, we identify and study factors that have played key roles in many extinctions. We finish with a review of recovery efforts at the species and community levels. concept outline 59.1 Overview of the Biodiversity Crisis Prehistoric humans were responsible for local extinctions Extinctions have continued in historical time Endemic species hotspots are especially threatened 59.2 The Value of Biodiversity The direct economic value of biodiversity includes resources for our survival Indirect economic value is derived from ecosystem services Ethical and aesthetic values are based on our conscience and our consciousness 59.3 Factors Responsible for Extinction Amphibians are on the decline: A case study Habitat loss devastates species richness Overexploitation wipes out species quickly Introduced species threaten native species and habitats Disruption of ecosystems can cause an extinction cascade Loss of keystone species may disrupt ecosystems Small populations are particularly vulnerable 59.4 Approaches for Preserving Endangered Species
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Destroyed habitats can sometimes be restored Captive breeding programs have saved some species 59.5 Conservation of Ecosystems 1237 rav65819_ch59_1237-1260.indd 1237 rav65819_ch59_1237-1260.indd 1237 12/6/06 12:08:48 PM 12/6/06 12:08:48 PM 59.1 Overview of the Biodiversity Crisis Extinction is a fact of life. Most species—probably all—become extinct eventually. More than 99% of species known to science (most from the fossil record) are now extinct. Current rates of extinction are alarmingly high, however. Taking into account the current rapid and accelerating loss of habitat, especially in the tropics, it has been calculated that as much as 20% of the world’s biodiversity may be lost by the middle of this century. In addition, many of these species may be lost before we are even aware of their existence. Scientists estimate that no more than 15% of the world’s eukaryotic organisms have been discovered and given scientific names, and this proportion is probably much lower for tropical species. These losses will affect more than poorly known groups. As many as 50,000 species of the world’s
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rav65819_ch59_1237-1260 - ; 59 chapter introduction...

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