Study foresees a rapid and widespread extinction of species

Monday, March 7, 2011; 7:31 PM

About the looming extinction of most animal species: The news isn't all bad.

Earth's creatures are on the brink of a sixth mass extinction, comparable to the one that wiped out the dinosaurs. That's the conclusion of a new study, which calculates that three-quarters of today's animal species could vanish within 300 years.

"This is really gloom-and-doom stuff," says the study's lead author, paleobiologist Anthony Barnosky of the University of California at Berkeley. "But the good news is, we haven't come so far down the road that it's inevitable."

Species naturally come and go over long periods of time. But what sets a mass extinction apart is that three-quarters of all species vanish quickly. Earth has already endured five such events, including one that wiped out dinosaurs and many other creatures 65 million years ago. Conservationists have warned for years that the world is in the midst of a sixth, human-caused extinction, with species from frogs to birds to tigers threatened by climate change, disease, loss of habitat and competition for resources with nonnative species.

But how does this feared new extinction compare with the other five?

Barnosky and colleagues took on this question by looking to the past. First, they calculated the rate at which mammals, which are well represented in the fossil record, died off in the past 65 million years, finding an average extinction rate of fewer than two species per million years. But in the past 500 years, at least 80 of 5,570 species of mammals have gone extinct, according to biologists' conservative estimates. This extinction rate is actually higher than those documented for past mass extinctions, says Barnosky.

This means that Earth is at the beginning of a mass extinction that will play out over hundreds or thousands of years, his team concluded in their paper, which was published online last week by the journal Nature.

The picture gets even grimmer when all mammals currently endangered or threatened are added to the count. If those all disappear within a century, 75 percent of all mammal species will be gone 334 years from now, says Barnosky. "Look outside of your window. Imagine taking away three-quarters of the living things you see, and ask yourself if you want to live in that world."

The team extended the same methods of analysis to amphibians, reptiles, birds, plants, mollusks and other forms of life and found similar patterns.

The silver lining in this dark cloud is that if humans work quickly to protect endangered and threatened species and their habitats now, the mass extinction can be prevented or at least delayed by thousands of years, says Barnosky.

- Ann Gibbons

This article was produced by ScienceNOW, the online daily news services of Science magazine, and can be read at news.sciencemag.org.


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