animals

No single cause for Ice Age extinctions

TEXAS A&M (US) —Neither climate change nor humans alone can account for the Ice Age mass extinctions, according to a new international study.

The extinctions caused the loss of a third of the large-bodied mammals (commonly called megafauna) such as the woolly rhinoceros and woolly mammoth in Eurasia and two thirds of the large mammals in North America. Scientists have for years debated the reasons behind the extinctions.

“Our findings put a final end to the single-cause theories of these extinctions,” says Eske Willserslev, professor of biology at the University of Copenhagen who, with his group from the Centre for GeoGenetics, led the study with researchers from 40 universities around the world.

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“Our data suggest care should be taken in making generalizations regarding past and present species extinctions; the relative impacts of climate change and human encroachment on species extinctions really depend on which species we’re looking at.”

Published in Nature, the study reports that climate alone caused extinctions of woolly rhinoceros and musk ox in Eurasia, but a combination of climate and humans played a part in the loss of bison in Siberia and wild horse. While the reindeer remain relatively unaffected by any of these factors, the causes of the extinction of the mammoth remain unresolved.

The study also reports that climate change has been intrinsically linked with major population size changes over the past 50,000 years, supporting the view that populations of many species will decline in the future owing to climate change and habitat loss. There was no clear pattern in the data distinguishing species that went extinct from species that survived.

“The fact that we couldn’t pinpoint what patterns characterize extinct species—despite the large and varying amount of data analyzed—suggests that it will be challenging for experts to predict how existing mammals will respond to future global climate change,” says Eline Lorenzen, a professor at the University of Copenhagen and lead author of the study. “Which species will go extinct and which will survive?”

“The bottom line is that we really don’t know why some of these ancient species became extinct,” adds Ted Goebel, professor of anthropology at Texas A&M University.

“Now we can better predict what might happen to animals in the future as climate change occurs. What happens to species when their ranges are significantly diminished, and why do some animals adapt successfully while others become extinct?  We now have a genetic roadmap to follow in our efforts to protect sensitive animal populations—especially in drastically impacted regions like the Arctic.”

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