The rate of extinction of species of plants and animals in our time is quite high. This is noted by many scientists. In some regions of the Earth, biodiversity is greatly reduced, and the number of large animals decreases. Biologists have started talking about the sixth global extinction, which, incidentally, came not without the participation of man. Opponents of similar alarmism insist that it is definitely possible to talk about the catastrophe through the century-another.
“The fact that there is a high rate of extinction of species now on the planet is an indisputable fact, it is another matter to accurately assess the tempo and compare it with the mass extinctions of past eras,” said Alexander Markov, head of the Department of Biological Evolution of the Faculty of Biology of Moscow State University M.V. Lomonosov.
Paleontologists argue that some background extinction of species, as well as the emergence of new ones, takes place on the planet all the time. But now species disappear a thousand times faster than in calm prehistoric times. This conclusion was reached by the authors of the international research project “Millennium Ecosystem Assessment”, the results of which were published back in 2005. According to scientists, disappearance threatens 10-30% of species.
In 2009, Australian biologist Nigel E. Stork (Nigel E. Stork) analyzed the rate of extinction predicted by various researchers. The spread turned out, at first glance, impressive: every ten years the planet loses from tenths of a percent, for example among insects, to tens of percent of the total number of species.
“Even 1-2% is very much, it means losing every hundredth kind in ten years on the planet, and if 20-30%? Yes, it looks like a large mass extinction,” Markov commented on Stork’s work.
“Our results confirm that the current rate of extinction is higher than can be expected by studying the fossil record, which proves the need for effective conservation measures,” write the authors of the survey entitled “Has the Earth’s sixth mass extinction already arrived?” (Has the sixth mass extinction of species on Earth already come?), Published in 2011 in Nature. And although scientists answer this question negatively, but given the unique and extremely unfortunate combination of conditions, it is stipulated that the world is only a few generations from a global extinction comparable to those that happened millions of years ago.
Who will die first
“Extinction primarily affects the richest ecosystems-tropical forests, coral reefs.In Brazil and Africa, the areas of wet equatorial forests are actively shrinking, which is a severe blow to biodiversity.When cutting 10 square kilometers of forest in the Amazon, this leads to the destruction of dozens and hundreds of species of mollusks, plants, insects.If we want to preserve the species richness of the planet, the tropics can not be touched, “says Alexander Markov.
Coral polyps of the Great Barrier Reef perish from warming of water
Coral reefs in the oceans are the second most vulnerable ecosystem. It was strongly influenced by the increase in the average annual global air temperature. Because of the heating of the upper oceanic layer, photosynthetic algae living with polyps in symbiosis are dying. Because of this, coral reefs become discolored, and their richest community of inhabitants dies.
“This is a very frightening process, taking place in warm seas,” the scientist emphasizes.
Extinction of land and freshwater mollusks was devoted to a recent publication in the journal Nautilus biologists from France and the United States. According to their version, snails and different bivalves do not tolerate habitat destruction, alien species attacks and climate change. Harm them and collectors. Over the past five hundred years 1032 species of mollusks have died out or otherwise disappeared from nature.
There are more chances to disappear in large animals, believes Leonard Polishchuk, a leading researcher at the Department of General Ecology of the Faculty of Biology, Moscow State University. To this conclusion he came, studying the extinction of mammoth fauna in the Pleistocene. The fact is that large animals do not form numerous populations, in other words, elephants are smaller than mice. If the population of large animals decreases under the influence of some factors, then the genetic diversity of the species decreases, harmful mutations pile up, which push animals to extinction. A positive feedback is built up, when some factors reinforce others, and as a result the species disappears.
“There are cases when species recovered after a sharp decline in numbers, the most famous example being cheetahs, judging by their genes, they passed through a very narrow bottle neck five to ten thousand years ago, figuratively speaking, but there were only a few dozen of them. miraculously survived, all modern cheetahs are the descendants of those single animals, “Markov cites.
American botanist Peter Raven (Peter Raven) in a recent article “The Fate of the World’s Plants” (Fate of the Flora) admits that half of the flora species are threatened with extinction before the end of the century. And most of them will remain unknown to us.
But the Stork mentioned by us back in 2013 argued the opposite in a witty work entitled “Will we be able to count all species before they die?” Without sharing the hypothesis of the sixth mass extinction, the scientist and his co-authors listed factors that prevent us from really assessing the rate of biodiversity loss: these are species conservation efforts, man-made landscapes with many species, extinction debt, which lags behind their reasons, as well as the notorious human factor. After all, to the disappearance of 90% of the known species of birds and mammals in the past five hundred years, people have somehow put their hand.
Super efficient megadocine
“About 40,000 years ago, when people entered Australia, large animals began to die out there in large numbers, most likely, it is directly related to humans.” The Australian megafauna was not adapted to co-existence with such a super-efficient predator as man, “explains Alexander Markov.
A similar fate befell the megafauna of the Americas 11-12 thousand years ago, when it was first populated by people. They directly or indirectly destroyed mammoths, mastodons, giant armadillos, sloths, horses. The last years later, the Spaniards brought Europe from Europe, horrified by the indigenous people.
Man and climate have made an equal “contribution” to the extinction of the megafauna of the glacial period
Approximately at the same time, the megafauna in the tundra-stages of Eurasia considerably thinned. Mammoths, cave lions and bears, woolly rhinoceroses and ancient horses have died out. As scientists believe, several reasons contributed to the disappearance, including the interglacial offensive. And in addition, at that time, the well-organized ancient hunters with bows and spears settled out of the glacier. According to Markov, the role of man in the extinction of large animals of the late Paleolithic can be said to have been proved.
Climate and life
Climate change (regardless of the causes that cause it) is considered as one of the main factors of the current extinction of species. This connection was investigated by scientists from Russia and the United States, taking as a basis the mathematical model of the emergence of chaos in the population of organisms. They added positive feedback to the model when the climate affects the ecosystem and vice versa.
“There are enough resources and a good climate, and the species are dying out in large numbers.” It seems that there is no logic, but it turns out that positive feedback is working, “says Ivan Sudakov, co-author of the work, the Department of Physics at the University of Dayton in the United States.
In another article, published so far in Arxiv.org, the same authors showed that the population of organisms, having reached the maximum diversity, having many resources, may die out from a small fluctuation in the climate.
Are such models applicable to our time? This possibility is admitted by Daniel H. Rothman of MIT in a recent article “Thresholds of catastrophe in the Earth system.” He analyzes the saturation of the Earth’s atmosphere with carbon dioxide over the past 540 million years, trying to understand when and under what conditions the discord of key systems of the planet begins, leading to the extinction of species.
The earth has experienced five catastrophes, losing most of the inhabitants as a result of restructuring the atmosphere, volcanic activity, asteroid attack and a combination of a wide variety of circumstances. After each episode, the living world was restored millions of years. Will he survive the sixth?