A Survey of Current Issues
Edited by Henk Folmer and Tom Tietenberg
Chapter 4: Strategies to conserve biodiversity
Stephen Polasky INTRODUCTION For many biologists the loss of biodiversity is perhaps the single most important environmental issue at the beginning of the 21st century (see for example, Myers, 1979; Wilson, 1992, 2002; Levin, 1999; Pimm, 2001; McKee, 2003). A 1998 survey of 400 biological scientists found that ‘the rapid disappearance of species was ranked as one of the planet’s gravest environmental worries, surpassing pollution, global warming . . .’ and other threats (Warrick, 1998). Several studies estimate that current rates of extinction are several orders of magnitude above the average extinction rate through geologic time (Lawton and May, 1995; NRC, 1995; Pimm et al., 1995). Loss of tropical forests where a large portion of global biodiversity resides is of particular concern. What is known about present and past rates of extinction, and estimates of future extinction rates, however, is far from conclusive. Projections of how many species are likely to go extinct over the coming century often use species-area curve relationships, which predict the total number of species as a function of the total size of the area that species could inhabit (MacArthur and Wilson, 1967). Predictions of large-scale extinction come from combining the species-area curve relationship with projections of current and future habitat loss. Using this approach Wilson (1999) estimated that 27 000 species a year are likely to go extinct. Skeptics claim that biologists have vastly overestimated the loss of biodiversity (e.g., Lomborg, 2001). Fewer than 1000 species have been documented as having gone extinct since 1500 (IUCN, 2003)...
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