"Bleak" is how conservationists are characterizing the future of the world's mammals. Today at its quadrennial congress in Barcelona, Spain, the International Union for Conservation of Nature (IUCN) released its long-awaited database detailing the status of all mammals known to humankind since the year 1500. The analysis estimates that at least one quarter of the 5487 species are threatened with extinction and that one half are declining in number.
The database, part of the IUCN Red List of Threatened Species, updates and expands a survey from 1996 and includes both land and marine species. Taking 5 years to compile, the effort involved more than 1700 researchers from 130 countries. They combed their literature and pooled their unpublished knowledge of ecology, taxonomy, distribution, population trends, threats, and conservation efforts. The species were then classified according to their extinction risk. "We wanted to make this one-stop shopping for scientists and policymakers," says IUCN and Conservation International mammalogist Jan Schipper, who coordinated the project.
For some species, data were quite detailed, down to individual breeding rates. But many others remain virtually unknown. "We don't really know as much as we thought we knew," Schipper says. Particularly sparse were data on some rodents and bats, several of which are known just from single museum specimens collected from remote regions. In all, 836 species were so poorly studied that it was impossible to tell what their conservation needs might be.
The good news is that well-funded conservation programs are succeeding. One example cited by Schipper is the recovery of the black-footed ferret in the United States. After ranchers destroyed its prey, prairie dogs, the ferret disappeared. But in the early 1980s, a small population was discovered in Wyoming and brought into captivity for breeding by the U.S. government. Over the past 20 years, the ferret has successfully been reintroduced in several U.S. states (Science, 12 May 2000, p. 985).
Also encouraging is the diversity of mammals, which is richer than previously thought. Taxonomists have described 349 newly discovered mammals since 1992, including an elephant shrew from Tanzania early this year. All told, there are 700 mammals in this survey that were not covered in 1996.
The bad news is that 188 species are critically endangered, and 29 of them, such as a freshwater dolphin from China called a baiji (Science, 22 December 2006, p. 1860), may already be extinct. Since 1996, the risk categories and mammal classification schemes have changed, making it difficult to directly compare 1996 data with the new information, says Schipper. The analysis identifies habitat loss and hunting as the biggest reasons behind the decline of land mammals; marine species face additional threats, including pollution and accidental death in fishing nets. Large mammals, particularly hoofed animals and primates in South and Southeast Asia, are the worst off, Schipper's team will report 10 October in Science. Marine mammals are most at risk in the North Pacific, the North Atlantic, and Southeast Asia.
All told, extinction looms large for 1139 out of the 4651 species for which there are good data. About half the species are declining in numbers, including one in five of those not at risk for extinction right now.
The new database "is the most valuable effort to date to summarize the state of conservation and threats to the world's mammal populations," says mammalogist Don Wilson of the Smithsonian National Museum of Natural History in Washington, D.C. "By detailing threats at the species level, it will now be possible for management agencies in every country in the world to prioritize their efforts to try to mitigate these threats."
There will likely be a payoff for basic research too, says mammalogist Gerardo Ceballos of the National Autonomous University of Mexico, who in 2005 compiled a similar database encompassing about 4500 mammals. These databases can reveal large-scale patterns of species distributions, Ceballos says, and their relationship to climate change and extinctions.