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Species extinction rates may be lower than thought, study finds


A polar bear walks on the frozen tundra on the edge of Hudson Bay outside Churchill, Manitoba, Canada. Polar bears return every year to Churchill, the polar bear capital of the world, where they remain hunting for seals on the icepack until the spring thaw.


Paul J. Richards

A controversial study suggests that current extinction rate projections of animal and plant species may be overestimating the role of habitat loss. But researchers said that species extinction still remains a “real and growing" threat.

Current methods of estimating extinction rates are flawed, using the wrong kind of data, and fail to take into account the full complexity of what influences species loss, researchers found.

The study, published in the journal Nature, said that present figures overestimated rates by up to 160 percent, and called for more accurate calculations. Animals and plants are dying out about 2.5 times more slowly than previously thought, according to the study’s authors, Stephen Hubbell from the University of California Los Angeles and Fangliang He from Sun Yat-sen University in Guangzhou, China, who is currently on sabbatical from Canada's University of Alberta.

The study notes that several predictions, including one that predicted half of all species would be gone by the year 2000, "have not been observed."

"The most widely used indirect method is to estimate extinction rates by reversing the species-area accumulation curve, extrapolating backwards to smaller areas to calculate expected species loss," the researchers wrote. "Estimates based on this method are almost always much higher than actually observed."

"The area that must be added to find individual of a species is, in general, much smaller than the area that must be removed to eliminate the last individual of a species," the professors observed. "Therefore, on average, it takes a much greater loss of area to cause the extinction of a species."

But Hubbell and He also wrote that habitat loss was still the main threat to biodiversity, and that the study must not "lead to complacency about extinction (as a result of) habitat loss," which was a "real and growing concern,” the BBC reports.

The study has been criticized by some prominent ecologists, who expressed concerns about the paper’s sweeping conclusions, The New York Times reports.

Stuart Pimm, a conservation biologist at Duke University in Durham, North Carolina, called the study "total nonsense" and told Postmedia News that Hubbell and He have misrepresented his work on species loss in North America's eastern forest.

Jean Christophe Vie, species program deputy director for the International Union for Conservation of Nature — which publishes the authoritative Red List of Threatened Species — said that while it is important to “get the science right,” he was concerned about how the study could be interpreted.

"I am quite worried about how this report could be used by people who are reluctant to take environmental issues seriously," he told the BBC.