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Scientists: Species Extinction Rates Are Greatly Overestimated

A scuba diver swims in this handout photo from the journal Science (file photo)
A scuba diver swims in this handout photo from the journal Science (file photo)
Jessica Berman

A team of scientists claims that a widely-used formula for calculating whether certain plant and animal species are becoming extinct is deeply flawed, and might overestimate extinction possibilities by as much as 160 percent. The researchers say that while their finding suggests a less rapid rate of global extinctions, serious threats remain to the survival of many plant and animal species.

Back in the early 1980s, environmental biologists predicted that as many as half of the world’s species of plants and animals would be lost by the year 2000.

That did not turn out to be the case, according to a team of Canadian and American researchers. They say a new analysis of a mathematical formula widely used to calculate extinction rates shows the world’s flora and fauna may have a little more time.

While it’s true that the Earth is losing plant and animal species at a rate that’s faster than at any time since the last major mass extinction 65 million years ago, a tropical forest ecologist at the University of California Los Angeles, Stephen Hubbell, said the situation is not as dire as everyone thinks.

Hubbell said the fundamental formula used by ecologists for the last quarter-century to calculate extinction rates is fundamentally flawed.

“So what this shows is that many of us, many scientists, can be led away from the right answer by thinking of the problem in the wrong way," he said. "And so, once the problem was formulated in the right way, then the answer was relatively straightforward.”

Hubbell and co-researcher Fangliang He at the University of Alberta in Canada say they disproved the conventional extinction formula, called a “species area relationship,” using data from the Center for Tropical Forest Science, a global network of forest research plots maintained by the Smithsonian Institution in Washington.

The plots, located throughout Asia, Africa, South America and Central America, contain more than four million individually catalogued trees representing 8,500 species. Researchers say if the trees go extinct, so will animals that depend on them for survival.

To determine whether a species is headed for extinction, scientists count the number of plants and animals encountered in areas of different sizes to come up with the species-area relationship. Then, they extrapolate backwards to predict how many species will be lost as their habitats shrink due to human encroachment and other forms of habitat destruction.  

Hubbell said there’s a problem with this counting strategy.

“It makes the assumption that if you lose the first individual [animal in a species] you encounter, that species is committed to extinction, and clearly that isn’t true," he said. "You have to lose them all.”

Hubbell said that to calculate extinction more accurately, scientists need to keep increasing the land area they sample rather than decreasing it. According to their mathematical formula, Hubbell said the problem of species extinctions is not as dire as is widely believed.

“This is welcome news in the sense that we have bought a little time for saving species," he said. "But it is unwelcome news in one sense, because we have to redo a lot of research that was done incorrectly as a result of the incorrect method.”

The researchers say they are 100 percent sure of the accuracy of their new extinction formula. But Hubbell said the disappearance of plant and animal species around the globe remains a serious problem, as humans continue to infringe upon rain forests, which experts believe are home to some three-quarters of the world’s species.

An article by scientists on their revised method for calculating species extinction rates is published in the journal Nature.

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