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COPYRIGHT 2004 Natural History Magazine, Inc.
Think of an outdoor place where you like to walk. Take a moment and picture what you expect to see: familiar trees and flowers, perhaps singing robins or squawking jays. Think of your favorites, the plants and animals you look for, the pleasure and even reassurance that seeing them brings. What if, the next time you went for that walk, you found that half of your favorites were missing; that still fewer were around the next time; and that, by the third trip, everything you treasured most had disappeared? It would be painfully sad, of course, but wouldn't it seem odd, as well? If all the squirrels, say, or house sparrows in the eastern United States were to suddenly disappear, the first questions on everyone's lips would be: What happened? Why are they gone?
Unfortunately, for biologists studying the Earth's biodiversity, discovering that a familiar organism is suddenly gone is an all-too-familiar experience. Sometimes the explanation is easy. The unmistakable marks of a chain saw on tree stumps provide obvious clues. But more often the answer is not so clear-cut.
By profession I am a herpetologist, a biologist specializing in reptiles and amphibians. In the late 1980s, my colleagues and I began reporting that in familiar amphibian haunts the numbers of flogs and salamanders were declining. By the mid-1990s we were hearing reports that species were going extinct in only a few years; the search for the answer to our question--why are they gone?--was becoming paramount.
Actually, our search became a quest for answers (plural!): the reality in the science, as in any good mystery, turned out to be complicated. In fact, the full story of the decline and extinction of amphibian species remains unknown. But the dimensions of the problem are easier to appreciate if the leading explanations are split into two major categories, the historical and the recent.
Historical explanations point to such causes as competition with exotic, introduced species, or predation by the same; to the harvesting of wild animals for food or pets; and to changes in patterns of land use. Those processes account for most of the damage to amphibian populations for much of the twentieth century, and even today. Although the details of how one of these pressures caused a species to disappear may elude biologists, historical stresses often leave clues--some as obvious as the mark of a chainsaw--from which an investigation can begin.
Of course, none of these...
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