Wednesday, April 2, 2008

Humans were final cause of woolly mammoth extinction

The woolly mammoth was driven to extinction by our ancestors, after the giant creatures had been pushed to the brink by climate change, marking a milestone in the destructive effects of mankind on the Earth's ecosystems.

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  • Woolly mammoths first appeared in Eurasia around 300,000 years ago. They died out around 5,000 years ago, long after the end of the last Ice Age.

    Mammoth found in Siberia, 1903: Humans, not climate change, were the final factor in causing woolly mammoth extinction

    These magnificent creatures, who had bigger brains than us, would have crossed the paths of our ancestors many times but scientists have been unsure whether climate change or human hunting caused their demise, because it is difficult to untangle these two potential causes of extinction, as climate change led to increased human hunting.

    Work by Dr David Nogués-Bravo of the Museo Nacional Ciencias Naturales, Madrid, and colleagues has ended the debate, by using mathematical modelling to disentangle the factors, showing that human hunting was the final straw.

    A study by the team, published in PLoS Biology, uses climate models and fossil distribution to establish that the woolly mammoth went extinct primarily because of loss of habitat due to changes in temperature, but concludes that human hunting delivered the "coup de grace," as Dr Nogués-Bravo puts it.

    To come to this conclusion the team predicted climate and species distribution at different times in mammoth history - 126,000, 42,000, 30,000, 21,000, and 6,000 years ago - considering temperature and rainfall simulations alongside the age and locations of fossils.

    This reveals that the mammoth suffered a catastrophic loss of habitat, with the species 6,000 years ago relegated to ten per cent of the habitat available to it 42,000 years ago (when the glaciers covered the greatest extent).

    But the final nail in the mammoth's coffin was that the mammoth also came into contact with modern humans. The team estimates that, even using an optimistic estimate of mammoth numbers 6000 years ago, humans would only have had to kill one mammoth each every three years to push the species to extinction. Using pessimistic figures, that falls to just one mammoth per human every 200 years.

    Disentangling the effects of climate and hunting has been tricky because when the climate in mammoth territory became too warm for the furry beast, it allowed humans - who couldn't easily handle the chilly, mammoth-friendly temperatures - to move into the area.

    Therefore, the mammoth faced the heat and pressure from hunting in the same places at approximately the same times, making it difficult to test the importance of the two factors independently.

    It had also been argued that, as the mammoth had survived many temperature fluctuations previous to those that coincided with its demise, it was only human hunting that was a substantially different condition that could have caused the extinction of the species.

    But the new study by Dr Nogués-Bravo shows that, in the case of the mammoth, it was the climate that forced the species to the point of extinction, and it was mankind that gave the woolly beast the last shove into oblivion and the history books.

    Original here

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