Beitrag Mi 17. Feb 2021, 11:30

Climate Change Likely Drove The Extinction Of North America

Climate Change Likely Drove The Extinction Of North America’s Megafauna


A new study published in Nature Communications suggests that the extinction of North America's largest mammals was not driven by overhunting by rapidly expanding human populations following their entrance into the Americas. Instead, the findings, based on a new statistical modelling approach, suggest that populations of large mammals rapidly declined in response to climate change about 13,000 years ago.

Before around 10,000 years ago, North America was home to many large and exotic creatures, such as mammoths, gigantic ground-dwelling sloths, giant beavers, and huge armadillo-like creatures. But by around 10,000 years ago, most of North America's animals weighing over 44 kg, also known as megafauna, had disappeared.

The main cause of the extinction has been intensely debated for decades, with most researchers arguing that human overhunting, a global natural disaster, deadly pathogens or climate change was responsible. With a new statistical approach, researchers from the Max Planck Extreme Events Research Group in Jena found strong evidence that climate change was the main driver of extinction.

Since the 1960's, it has been hypothesized that, as human populations grew and expanded across the continents, the arrival of specialized "big-game" hunters in the Americas some 14,000 year ago rapidly drove many giant mammals to extinction. The large animals did not possess the appropriate anti-predator behaviors to deal with a novel, highly social, tool-wielding predator, which made them particularly easy to hunt. According to proponents of this "overkill hypothesis", humans took full advantage of the easy-to-hunt prey, devastating the animal populations and carelessly driving the giant creatures to extinction. But many scientists have argued that there is too little archaeological evidence to support the idea that megafauna hunting was persistent or widespread enough to cause extinctions. Instead, significant climatic and ecological changes may have been to blame.

Around the time of the extinctions (between 15,000 and 12,000 years ago), there were two major climatic changes. The first was a period of abrupt warming that began around 14,700 years ago, and the second was a cold snap around 12,900 years ago. During the Younger Dryas, the Northern Hemisphere returned to near-glacial conditions for about a thousand years. One or both of these important climate swings, and their ecological ramifications, have been implicated in the megafauna extinctions.

"A common approach has been to try to determine the timing of megafauna extinctions and to see how they align with human arrival in the Americas or some climatic event," says Mathew Stewart, co-lead author of the study. "However, extinction is a process—meaning that it unfolds over some span of time—and so to understand what caused the demise of North America's megafauna, it's crucial that we understand how their populations fluctuated in the lead up to extinction. Without those long-term patterns, all we can see are rough coincidences."

To test these conflicting hypotheses, the authors used a new statistical approach developed by W. Christopher Carleton, the study's other co-lead author, and published last year in the Journal of Quaternary Science.

Archaeologists and palaeontologists use the radiocarbon record as a proxy for past population sizes. The rationale being that the more animals and humans present in a landscape, the more datable artefacts and bones are left behind after they are gone, which is then reflected in the archaeological and fossil records. However, uncertainty associated with radiocarbon dates may suggest a false temporal correlation.

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