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Humans exterminate animal and plant species so quickly that the built-in defense mechanism of nature – evolution – can not keep up.
A research team led by Aarhus has calculated that if current conservation efforts are not improved, many mammal species will disappear over the next five decades and that nature will need three to five million years to come. to recover.
Five upheavals have taken place over the course of 450 million years, when the environment of our planet has changed so much that the majority of plant and animal species on Earth have disappeared. After each mass extinction, evolution gradually filled the gaps with new species.
The sixth mass extinction is happening now, but this time the extinctions are not caused by natural disasters; they are the work of humans. A team of researchers from Aarhus University and the University of Gothenburg calculated that the extinctions were evolving too fast for the evolution to continue.
If mammals diversify normally, they will need another five to seven million years to restore biodiversity to its level before the evolution of modern humans, and three to five million years to reach current levels of biodiversity, according to the published analysis. recently in the prestigious scientific journal, PNAS.
Some species are more distinct than others
The researchers used their extensive mammal database, which includes not only species that still exist, but also hundreds of species that lived in the recent past and disappeared after the spread of Homo sapiens across the world. This allowed the researchers to study the full impact of our species on other mammals.
However, not all species have the same meaning. Some extinct animals, such as the Australian lion Thylacoleo, similar to a leopard, or the strange Macrauchenia of South America (imagine a llama with an elephant trunk) were distinct evolutionary lineages and n & rsquo; Had only a few close relatives. When these animals disappeared, they took with them whole branches of the evolutionary tree of life. We have not only lost these species, we have also lost the unique ecological functions and millions of years of evolutionary history that they represented.
"Large mammals, or megafauna, such as giant sloths and saber-toothed tigers, which had died out about 10,000 years ago, were extremely evolutionary.As they had few close relatives, their extinctions have resulted in the cutting of entire branches of the Earth's evolving tree., "said Matt Davis, paleontologist at Aarhus University, who led the study. "There are hundreds of species of shrews, which allows them to resist a few extinctions.There were only four species of saber-tooth tigers, all of which have disappeared."
Long wait for rhinoceros replacement
Regenerating 2.5 billion years of evolutionary history is already quite difficult, but today 's mammals are also facing increasing extinction rates .
Critically endangered species such as the black rhinoceros are likely to disappear within the next 50 years. Asian elephants, one of only two surviving species of a once very powerful order, including mammoths and mastodons, have less than a 33% chance of surviving this century.
The researchers incorporated these expected extinctions into their calculations of the history of lost evolution and posed the question: can existing mammals naturally regenerate this lost biodiversity?
Using powerful computers, advanced evolutionary simulations and comprehensive data on the evolutionary relationships and size of extant and extinct mammals, researchers were able to quantify how long evolution would be lost with past extinctions and potential futures, as well as recovery time.
The researchers have developed an optimistic scenario for the future, in which humans have stopped destroying their habitats and eradicating species, thus reducing extinction rates at low background levels observed in the fossils. However, despite this overly optimistic scenario, it will take mammals between three and five million years to diversify sufficiently to regenerate the branches of the evolutionary tree that they should lose over the next 50 years. . It will take more than 5 million years to regenerate what has been lost from giant species of the ice age.
Prioritize conservation work
"Even if we once lived in a world of giants: giant beavers, armadillos and giants, giant deer, etc., we are now living in a world increasingly poor in wild mammals.The few remaining giants, such as rhinos and Elephants are at risk of disappearing very quickly, "said Jens-Christian Svenning of Aarhus University, who runs a large megafauna research program that includes the study.
The research team, however, has not only bad news. Their data and methods could be used to quickly identify endangered, evolutionarily different species, so that we can prioritize conservation efforts and focus on ways to avoid extinctions. the most serious ones.
"It's a lot easier to save biodiversity now than to change it later," said Davis.
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