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How long does it take species to go extinct? Longer than previously thought.

Habitat destruction drives species extinct more slowly than previously thought, according to a new model described in this week's Nature. 'We have bought a little time for saving species,' says scientist.

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Once they had a new mathematical approach in hand, they used old and new methods to calculate extinction rates for eight well-studied small forest plots in China, Taiwan, Panama, Ecuador, Malaysia, Cameroon, as well as two far broader regions in the US that are home to some 279 species of perching birds. The new, more-nuanced approach gave significantly lower extinction rates from lost habitat than the old.

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"This is a really cool analysis," says Peter Kareva, chief scientist for the Nature Conservancy in Arlington, Va. For an ecologist, the distinction He and Hubbell draw between the old and proposed new approaches "is kind of obvious. I wonder how this has been overlooked" for so long, he says.

Others are touch more cautious.

Hubbell has long been known in the field for "developing an intellectual framework that allows people to test ecological and conservation ideas," says Richard Primack, a conservation biologist at Boston University.

This new approach to estimating extinction rates "is taking ideas that were generally out there and providing a rigorous model which hundreds of people will start testing over the next few years," he says.

No more 'magic number'?

Another team has looked at the extinction question from a different perspective. Their research, accepted for publication in the journal Trends in Ecology and Evolution, suggests that using a single, universal "minimum viable" population number – to gauge which endangered plants or animals to try to save – is seriously flawed.

It fails to account for important changes such as climate, loss of habitat, or encroachment by invasive species, or whether the population is growing or decling – all of which can play key roles in a species' survival.

Dr. Beissinger and colleagues felt the use of a "magic number" for identifying a viable minimum population of organisms "was a bit of an oversimplification," he says.

Among other problems, the single benchmark can lead policymakers to declare a species saved when it may be anything but, he adds.

Some conservation specialists have used the approach as a tool for triage. "Should we continue to try to save the California condor, when there are 20 rare Hawaiian plants we could probably save with the same budget?" Beissinger asks rhetorically.

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