[ad_1]
Illustration of how smaller mammals will have to evolve and diversify over the next 3 to 5 million years to compensate for the loss of large mammals. Credit: Matt Davis, University of Aarhus
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 3 to 5 million years to get well.
Over the 450 million years, the environment has changed so much that five upheavals have taken place, resulting in the disappearance of the majority of plant and animal species on the planet. 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 5 to 7 million years to restore biodiversity to its level before the evolution of modern humans, and 3 to 5 million years to reach current levels of biodiversity, according to the published analysis. recently in 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.
The Litopterns, like that Macrauchenia patachonica discovered by Charles Darwin, constituted a strange group of South American prehistoric mammals that were not related to any living species today. They evolved evolutionarily from other mammals more than 65 million years ago. When they died out at the end of the ice age, the mammal Tree of Life lost one of its deepest branches. Credit: Robert Bruce Horsfall [Public domain], via Wikimedia Commons
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) constituted 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 evolutionary tree of the Earth. "says paleontologist Matt Davis of Aarhus University, who led the study. And he adds:
"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?
The Indri secret (indri indri) of Madagascar is the largest living lemur. It is also critically endangered and very distinct from the point of view of evolution without close kinship, a combination that makes it a most precarious branch of the evolutionary tree of mammals. In the event that the indri disappears, we will lose 19 million years of the unique evolutionary history of the mammal of life. Credit: University of Aarhus
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 3 to 5 million years for mammals to diversify enough 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 threatened with being eliminated very quickly, "says Professor Jens-Christian Svenning of Aarhus University, who runs a large megafauna research program, which 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.
As Matt Davis puts it: "It is much easier to save biodiversity now than to make it evolve later."
Explore further:
For the first time, scientists put extinct mammals on the map
More information:
Matt Davis et al., "It will take millions of years for mammalian diversity to recover from the current biodiversity crisis" PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1804906115
Source link
