Study: World on verge of sixth great extinction

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Years ago, scientists found golden lion tamarins, once thought to be extinct, and bred them in captivity. Tamarins are still endangered in the wild because of threats to their habitats, according to the International Union for Conservation of Nature Red List of Threatened Species. (Stuart Pimm, Duke University/Associated Press)

Frances Sprouls

SETH BORENSTEIN
Associated Press

Years ago, scientists found golden lion tamarins, once thought to be extinct, and bred them in captivity. Tamarins are still endangered in the wild because of threats to their habitats, according to the International Union for Conservation of Nature Red List of Threatened Species.  (Stuart Pimm, Duke University/Associated Press)
Years ago, scientists found golden lion tamarins, once thought to be extinct, and bred them in captivity. Tamarins are still endangered in the wild because of threats to their habitats, according to the International Union for Conservation of Nature Red List of Threatened Species. (Stuart Pimm, Duke University/Associated Press)

WASHINGTON — Species of plants and animals are becoming extinct at least 1,000 times faster than they did before humans arrived on the scene, and the world is on the brink of a sixth great extinction, a new study says.

The study looks at past and present rates of extinction and finds a lower rate in the past than scientists had thought. Species are now disappearing from Earth about 10 times faster than biologists had believed, said Stuart Pimm of Duke University, the study’s lead author and noted biologist.

“We are on the verge of the sixth extinction,” Pimm said from research at the Dry Tortugas, a small group of islands at the end of the Florida Keys. “Whether we avoid it or not will depend on our actions.”

The work, published by the journal “Science” on Thursday, was hailed as a landmark study by outside experts.

Pimm’s study focused on the rate, not the number, of species disappearing from Earth. It calculated a death rate of how many species out of 1 million become extinct each year.

In 1995, Pimm found that the pre-human rate of extinctions on Earth was about one. But taking into account new research, Pimm and his colleagues refined that background rate to about 0.1.

Now, that death rate is about 100 to 1,000, Pimm said.

Numerous factors are combining to make species disappear much faster than before, said Pimm and co-author Clinton Jenkins of the Institute of Ecological Research in Brazil. But the No. 1 issue is habitat loss. Species are finding no place to live as humans build up and alter more places.

Other factors are invasive species crowding out native species, climate change affecting where species can survive and overfishing, Pimm said.

The buffy-tufted-ear marmoset is a good example, Jenkins said. Its habitat has shrunk because of development in Brazil, and a competing marmoset has taken over where it lives. Now, it is on the international vulnerable list.

The oceanic whitetip shark used to be one of the most abundant predators on Earth, and they have been hunted so much they are now rarely seen, said Dalhousie University marine biologist Boris Worm, who wasn’t part of the study but praised it. “If we don’t do anything, this will go the way of the dinosaurs.”

A vast majority of the world’s life has been snuffed out five times, in what have been called mass extinctions, often associated with giant meteor strikes. About 66 million years ago, one such extinction killed off the dinosaurs and three out of four species on Earth. The largest mass extinction was the Great Dying, which snuffed out about 90 percent of the world’s species about 252 million years ago.

Pimm and Jenkins said there is hope. Both said the use of smartphones and applications such as iNaturalist will help ordinary people and biologists find species in trouble. They said once biologists know where endangered species are, they can try to save habitats and use captive breeding and other techniques to save the species.

One success story is the golden lion tamarin. Decades ago, the tiny primates were thought to be extinct because of habitat loss, but they were then found in remote parts of Brazil, bred in captivity and biologists helped set aside new forests for them to live in, Jenkins said.

“Now there are more tamarins than there are places to put them,” he said.

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