Bio Lec 3 Sup 1


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CURRENT SCIENCE, VOL. 82, NO. 11, 10 JUNE 2002 1325 The future of biological diversity in a crowded world* Robert M. May Scientific advances over the past century have led to improvements in most peoples’ lives, in both developed and developing worlds. But increasingly we recognize that many of these benefits have not been produced in a sustainable way, particularly as human populations continue to grow and the diversity and abundance of many other species diminishes. What happens to our world, and to us and the creatures we share the world with, in the future depends on the actions we take now. HOW well do we know the world of plants, animals and micro-organisms with which we share this planet? The answer, by any one of a variety of objective measures, must be: not very well. First, estimates of the number of species that have been named and recorded (a simple factual question, like how many books in the library catalogue?) range from 1.4 to 1.8 million. Second, estimates of the total number of species present on earth today range over more than an order-of-magnitude, from a low of around 3 million to a high of 30 million or possibly much more. And third, we have even less idea of the rates at which species may currently be going extinct, as a result of habitat destruction and other consequences of human population growth. In this brief overview, I outline my own best guess of the answers to these three questions. For the number of distinct species named and recorded, I emphasize the uncertainties caused by unresolved synonymies. For the likely total number of living species, I set out my reasons for leaning to the lower end of the range of published estimates. And for present and likely future extinctions, I sketch a relatively precise approach, based on compa- rative rates of extinction, which avoids some of the imprecisions inherent in dealing with the total number of species. I end by discussing estimates of the costs of effective action, and more generally why we should care. How many species are there? The systematic naming and recording of species began relatively recently, with Linneaus’ standard work which in 1758 recognized some 9000 species. Today the total number of living species named and recorded has been estimated at around 1.7 to 1.8 million. Amazingly, no centralized catalogue exists. There are synoptic and computerized catalogues for some better-known groups, most notably birds and mammals. But more than half (roughly 56%) of all named species are insects, and the majority of these are still on card catalogues in individual museums and other collections. By one estimate, around 40% of all named beetle species are known from only one site, and many from only one specimen. In short, the amount of taxonomic effort varies very widely from group to group, with roughly one-third of all taxonomists working on vertebrates, another third working on the ten times more numerous plant species, and the remaining third working on invertebrate animals, which outnumber vertebrate species by at least a factor of 100 (see Table 1).
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