carnes@gargoyle.UUCP (Richard Carnes) (10/04/86)
From an article by Roger Lewin in *Science* 234: 14-15 (3 October 1986): ________________ The National Academy of Sciences (NAS) and the Smithsonian Institution last week jointly sponsored a national forum on what most biologists perceive as a global crisis: namely, the potential imminent extinction of perhaps half the world's species, mainly through deforestation. The gathering, which was aimed at educating the public and lawmakers alike, kicked off a fall season in which it appears as if biodiversity has become a hot topic. ... "There is no controversy among mainstream biologists that there is a crisis in biodiversity," said Paul Ehrlich of Stanford University.... Referring to estimates of a doubling of the human population during the next century he said, "This implies a belief that our species can safely commandeer some 80% of NPP [net primary production], a preposterous notion to ecologists who already see the deadly impacts of today's level of human activities." ... At its core, the concern over biodiversity centers on two numbers, each of which has a substantial degree of uncertainty about it. The first is the number of extant species in the world; and the second is the rate at which they are being lost. In addition to offering some new data on these points, the NAS/Smithsonian forum also added some historical perspective for their evaluation, by making comparisons with previous diversity crises in the history of life. ... The rate at which species might be going extinct depends directly on the scale of tropical deforestation, a subject on which there has always been a good deal of uncertainty and dispute. Norman Myers, an environmental consultant from Oxford, England, presented a figure of 92,000 square kilometers for the annual, irrevocable loss of tropical forest, with a similar area being grossly disrupted through shifting farming and some logging. "These figures are pretty robust," he said, "because they are based on remote sensing data [via satellite] of 78% of the relevant land surface." Estimates by the Food and Agriculture Organization and the United Nations Environment Program are somewhat lower, but nevertheless lead by extrapolation to a virtually complete destruction by the year 2135, which more or less coincides with the time at which the World Bank estimates that global population will plateau at 11 billion. With the forests vanished or largely disrupted, up to half the world's species of animals, plants, and insects would disappear too. ... According to David Raup, of the University of Chicago, a figure of 50% extinction would be closely comparable with the mass extinction of 65 million years ago, during which the dinosaurs finally disappeared together with 60 to 80% of the rest of the world's species. The difference between natural mass extinctions and the current extinction spasm, if indeed that is what it is, is twofold. First, unlike previous events, current losses involve large numbers of plant species. Second, the agent that is causing extinction -- namely, human intervention -- will persist, therefore potentially preventing the diversity rebound that typically occurs after natural events. The degree of ignorance about fundamental processes underlying diversity and its response to disturbance is profound. For instance, [Edward O.] Wilson notes that "the study of extinction remains one of the most neglected subjects in ecology." He added that "the magnitude and control of biological diversity is not just a central problem of evolutionary biology; it is one of the key problems of science as a whole." __________________ Richard Carnes