Environmental Problems, Their Causes, and Sustainability 1

According to biodiversity researchers, the greatestthreat to wild species is habitat loss (Figure 12-7),degradation, and fragmentation. In other words, manyspecies have a hard time surviving after we take overtheir ecological “house” and food supplies and makethem homeless.Deforestation of tropical forests is the greatesteliminator of terrestrial species followed by the destructionof wetlands and plowing of grasslands.Globally, temperate biomes have been affected moreby habitat loss and degradation than have tropical biomesbecause of widespread development in temperatecountries over the past 200 years. Emphasis is nowshifting to many tropical biomes.According to the Nature Conservancy, the majortypes of habitat disturbance threatening endangeredspecies in the United States are, in order of importance:agriculture, commercial development, water development,outdoor recreation (including off-road vehicles),livestock grazing, and pollution.Range 100 years agoRange today(about 2,300 left)Range in 1700Range today(about 2,400 left)Indian TigerBlack RhinoProbable range 1600Range today(300,000 left)African ElephantFormer rangeRange today(34,000–54,000 left)Asian or Indian ElephantFigure 12-7 Degraded natural capital: reductions in the ranges of four wildlife species, mostly the result ofhabitat loss and hunting. What will happen to these and millions of other species when the world’s humanpopulation doubles and per capita resource consumption rises sharply in the next few decades? (Data fromInternational Union for the Conservation of Nature and World Wildlife Fund)232 CHAPTER 12 Sustaining Biodiversity: The Species Approach