Sunday, October 1, 2023

“It is as serious as climate change, but less known”: the warning cry of scientists

With the rapid disappearance of many animal species, man is causing the loss of entire branches of the “tree of life”, according to a new study published on Monday, which warns of the danger of a sixth mass extinction.

The biodiversity crisis “is as serious as climate change,” but not as well known to the general public, laments Gerardo Ceballos, professor at the National Autonomous University of Mexico and co-author of this study published in the journal PNAS.

But there is “urgency”, because what is at stake is “the future of humanity”, he told AFP.

There are already numerous studies on the disappearance of species, but the specificity of this one is that it has analyzed the extinction of entire genera.

“I think this is the first time we’ve tried to evaluate the extinction rate at a higher level than the species,” Robert Cowie, a biologist at the University of Hawaii who was not involved in the study, told AFP. . “This demonstrates the loss of entire branches of the tree of life,” a representation of life first developed by Charles Darwin.

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The study shows that “we’re not just cutting off twigs, we’re using a chainsaw to get rid of the big branches,” added Anthony Barnosky, professor emeritus at the University of California, Berkeley.

73 extinct genera

The researchers relied in particular on the lists of extinct species from the International Union for Conservation of Nature (IUCN). They focused on vertebrate species (excluding fish), for which more data is available.

Of around 5,400 genera (comprising 34,600 species), they concluded that 73 of them had become extinct in the last 500 years, most in the last two centuries. First of all, birds, followed by mammals, amphibians and reptiles.

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To understand whether this rate is higher than normal, the researchers compared this result with the extinction rate estimated using very long-term trace fossils.

“Based on the extinction rate over the last few million years, you would expect two genera to go extinct, but we lost 73,” said Gerardo Ceballos. According to the study, the extinction of these 73 genera should have taken 18,000 years, not 500.

These estimates remain uncertain, many species are not even known and the fossil records are incomplete. But, according to the researcher, they are probably underestimated.

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The cause of these extinctions? Human activities, which destroy habitats for crops, infrastructure and other needs, but also overexploitation (overfishing, hunting, animal trafficking, etc.).

However, the loss of a genus can have consequences on the functioning of an entire ecosystem. With a possible “collapse of civilization” in the long term, argues Gerardo Ceballos.

“If you have a wall made of bricks, and each brick is one type, removing a brick is not going to cause the wall to collapse,” he compares. “But if you remove many more, then the wall falls. »

According to him, there is no doubt that this is the sixth mass extinction. However, it remains a matter of debate whether it has already begun, although all experts agree that the current rate of extinction is alarming.

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