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The Real Biodiversity Crisis

Phillip Levin, Donald Levin

Destined to Repeat

There is no reason to assume that basic evolutionary processes in the future will differ substantially from those in the past. So we would expect the total number of species ultimately to recover from the current mass extinction, even if people continue to meddle with the environment on a global scale. The alteration and fragmentation of existing habitats ensures that any future radiation of mammals, for instance, will not include large forms such as rhinoceroses, apes and big cats. But other species may do quite well.

Figure 2. Speciation and extinction rates vary widely . . .Click to Enlarge Image

Consider the differences in future prospects for primates and rodents. Primates have both high rates of speciation and high rates of extinction. Human activities will likely increase their rates of extinction but may well reduce their opportunities for speciation. In contrast, people may only marginally increase the rates of extinction for rodents, while perhaps promoting their speciation somewhat. The rate of speciation for rodents currently exceeds their rate of extinction by far. Thus, the future may bring a decline in primate variety and an increase in the kinds of rodents roaming about.

Such shifts could be even more dramatic at higher taxonomic levels. Groups with short generation times, small home ranges and great dispersal capabilities—many insects, for example—will clearly be at an evolutionary advantage in a world full of human disturbance and unstable, patchy habitats. (Interestingly, in the mass extinction at the end of the Cretaceous, there is no evidence of any major change in insect faunas.)

So people's activities today affect more than just the tally of species that may go extinct soon: Our actions will also influence the diversity of species that can evolve and persist for millions of years to come. Conservation efforts, therefore, should aim to do more than stem the near-term loss of species. Resources should be directed to ensuring that there will be a rebound in the diversity of plant and animal species, not just in their numbers.

How might one do that? One response to the current crisis is the preservation of biodiversity "hotspots," areas with exceptionally large numbers of endemic species. But a narrow focus on saving the greatest number of species possible risks losing important biological attributes. To minimize this problem, higher-level taxa, such as families, should be used in defining biodiversity hotspots and setting conservation priorities.

Consider, for example, tropical plants. Ghillean Prance at the Royal Botanical Gardens, Kew, has noted that Malesia—the tropical region running from peninsular Malaysia to Papua New Guinea and the Solomon Islands—contains fewer plant species but more plant families than the entire neotropics. Because the number of families probably provides a better measure of the diversity of characteristics and evolutionary potential than does the number of species, preserving the flora of Malesia should be of considerable concern to conservationists interested in maintaining a high degree of biodiversity over the long haul.

After the current spasm of extinction ends, the number of species may well return to past levels, but there will surely be fewer higher-level taxonomic groups than today. Such a wholesale shift in earth's biota will impoverish the planet for many millions of years to come. In our view, this is the real threat to biodiversity—not a decline in species per se, but a long-term erosion in the variety of biological characteristics and functions that grace the natural world.

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