Posted at 7:00 am.
We are in the middle of 6and extinction? This is a question posed in a 2008 review PNAS, herpetologist Vance Vredenburg of San Francisco State University. “I think we were among the first to use these words, especially in a scientific journal,” Vredenburg said today. Since then, evidence of the rapidity of current extinctions has continued to accumulate. But the issue remains unresolved. »
On the one hand, we have mass extinctions with the extinction of more than 75% of species in a few tens or hundreds of thousands of years, explains the frog specialist. On the other hand, we are seeing the extinction of 10% to 20% of species in a few centuries, that is, much faster. “We may take this rapidity as a sign of an inevitable process, but we have no evidence that the five mass extinctions had the same start. Personally, I would add that advances in synthetic biology and conservation programs are also game-changing. »
Mr. Vredenburg cites the increase in populations of several species of whales as well as the improvement in genetic diversity in American ferret populations due to biotechnology. “If we give up our efforts, we will have 6and extinction, says the California biologist. But we can probably avoid it. »
Climate change is for many a tipping point that will make 6and inexorable extinction. “We emit 100 times more CO2 than volcanoes,” notes Elizabeth Colbert, journalist New Yorker who published a book in 2014 6th extinctionPublished by Guy Saint-Jean.
Mme Colbert just posted a sequel, fish in the desert, published by Buchet-Chastel, which covers about ten technology programs to protect biodiversity and combat climate change. “We have taken control of the geology and the carbon cycle. The current human impact on biodiversity is only a glimpse of what is to come. »
Michael Hanna, New Zealand biologist who has just published a book. extinctions, Cambridge University Press, points out that with every one of the five mass extinctions the planet has known in 500 million years, the climate has been disrupted. “Greenhouse gas emissions need to be addressed for several reasons, but preventing a mass extinction is one of the most important. »
land and sea
So far, most extinctions have occurred on land, especially on islands with rare species that cannot migrate. However, traces of the remaining five mass extinctions have been found in marine sediments. Therefore, some biologists believe that we cannot talk about 6and extinction until there are signs of accelerated loss of marine biodiversity, said Douglas McCauley, a biologist at the University of California at Santa Barbara who specializes in the protection of large marine mammals.
“Others think that extinction on land is a canary in the mine and a harbinger of what is to come in the seas. Frankly, it’s too early to tell, but there are plenty of reasons to protect marine biodiversity. It is also certain that if the planet warms up a lot, the oceans will change dramatically and become more acidic, which will affect shellfish species. In 2016, McCauley published a study comparing the current marine extinction to five great extinctions. He showed that, unlike the five great extinctions, marine species currently affected are the largest.
Another part of the debate concerns invasive species, which are more abundant than ever due to species-promoting trade and climate change. These invasive species often cause the extinction of competing native species. But some biologists argue that in many cases they are better adapted to ecosystems and therefore make them stronger. And that in any case, problematic invasive species can be dealt with, as New Zealand does with rats.
“Yes, we can consider that there is a discussion about the level of global impact of invasive species on ecosystems, but this does not prevent us from worrying about it,” said Philippe Boucher, a biologist from the Sorbonne. He just published in a magazine Current biology indictment in favor of recognizing a real danger 6and extinction. “If I can make a comparison, linguists deplore the loss of marginal languages spoken by a few hundred people. So we have to fight the extinction of rare species. At the very least, according to Mr. Boucher, the genetics of as many species as possible should be documented, much like we do salvage archeology to document sites that would be destroyed by a dam or highway. “Biodiversity needs to be archived,” Boucher says.
Even if we don’t worry about 6and extinction, we should be alarmed by “defaunation”, a concept that describes the loss of a large number of individuals of a species. “We have seen a sharp decline in the median biological abundance of species,” explains Alexander Lis, a biologist at Manchester Metropolitan University who fights “extinction denial” in scientific forums.
“We have many animals on earth, but most of them are agricultural species. Insect populations, for example, are declining. We are not talking about the risk of extinction, but there is the problem of functional biodiversity. In order for a species to fulfill its role in ecosystems, a certain number of individuals is required. According to this concept, you can have a mass extinction without the complete extinction of several species, because “functional extinctions” will lead to the extinction of entire ecosystems.
History of extinctions
Michael Hanna, book author extinctionsdon’t like to talk about 6and extinction, even if he is convinced that we are heading for a mass extinction. “Yes, there have been five mass extinctions, but there have also been four other mass extinctions with more than half of the species gone, and a dozen other major extinctions. Each of these 19 extinctions changed the face of the Earth more than we have so far. I don’t think we can be satisfied with being 20and great extinction, not 6and mass extinction. »
For reference, five mass extinctions were identified in the 1970s and 1980s by American paleontologists David Raup and Jack Sepkosky. “They brought together all the available fossil data to show these five extinction rate peaks,” says Daniele Luigi Pinti, a biologist at the University of Quebec at Montreal (UQAM). “It was a huge undertaking at the time. »
Now the late Raup and Sepkoski have also put forward the idea that great extinctions occur every 26 million years, possibly due to an unknown solar cycle. “This extinction cycle has not really been demonstrated, but studies on this topic appear regularly, I just saw one pass,” says Mr. Pinty. The Montreal biologist notes that due to the lack of fossils, we don’t know when the mass extinction occurred until 500 million years ago. The idea that the species could go extinct was first proposed in 1796 by French anatomist Georges Cuvier about mammoths – at the time they were thought to have survived in the American West.
Mass extinctions over time
445 million years ago: Ordovician extinction; reason: significant fluctuations in sea level due to movements of the supercontinent Gondwana; 85% of species disappear.
370 million years ago: Devonian extinction; Cause: Sudden drop in oxygen levels in the oceans, possibly due to a supernova explosion or worsening volcanism; 83% of species disappear.
252 million years ago: Permian extinction; reason: increased greenhouse gas emissions due to volcanism or asteroids; 95% of species disappear.
201 million years ago: Triassic extinction; cause: asteroids and large sea level fluctuations due to movements of the Gondwana supercontinent; 80% of species disappear.
66 million years ago: Cretaceous extinction; cause: an asteroid that caused anomalous volcanism (this is the only mass extinction, the cause of which is almost determined); 76% of species disappear.
Source : extinctionsMichael Hanna, Cambridge University Press
- 50 million years
- The time it takes for enough new bird species to emerge to compensate for island species that have become extinct due to human colonization.
SOURCE : Current biology
- 100 to 1000 times faster
- Current extinction rate versus long-term extinction rate
SOURCE : extinctionsMichael Hanna, Cambridge University Press
- Percentage of species lost in five mass extinctions. The remaining extinctions are associated with fourteen other great extinctions and ordinary extinctions.
SOURCE : extinctionsMichael Hanna, Cambridge University Press