Climate the culprit in megafauna's demise

The Age , Tuesday, May 07, 2013
Correspondent : Bridie Smith
Humans can rest easy. According to scientists, climate change caused Australia's megafauna to become extinct, rather than human activity such as hunting and burning vegetation.

A literature review by Australian and US scientists has concluded that there is no evidence humans are to blame for the disappearance of super-sized animals such as the Diprotodon, a short-faced wombat the size of a rhinoceros.

Lead author and zoologist Stephen Wroe, from the University of NSW, said most species of Australian megafauna, including a marsupial lion known as Thylacoleo carnifex, had disappeared by the time humans arrived 45,000 to 50,000 years ago.

Professor Wroe said at their peak there were about 90 megafauna species. But by the time people arrived, just eight to 14 species remained.

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''The evidence is suggesting that megafauna was on a downward trajectory even before humans arrived,'' he said.

He said there was no clear evidence that any more than 50 of the 90 megafauna species survived even beyond 130,000 years ago.

The effect of the cooling planet on such gigantic animals was dire as key resources required for survival, such as water, began changing drastically.

''As things got colder, more water was locked up in the ice sheets,'' he said, adding that up to 70 per cent of the continent was ''truly arid'' desert. The impact was felt throughout the food chain, from the carnivorous predators to the herbivores, such as the 200-kilogram-plus Diprotodon.

''The big predators go extinct before the big herbivores because once the density of large prey goes below a certain threshold they starve to death,'' he said.

''The tough guys on the block are actually the first to go.''

The study by researchers from the universities of NSW, Queensland, New England and Washington used a range of data, including Antarctic ice cores and central Australian ancient lake levels to generate a picture of the climate over time. This was then studied in conjunction with megafauna fossil records.

Published in the Proceedings of the National Academy of Sciences on Tuesday, the findings are likely to stir debate on the topic, which has raged for more than 150 years. And Professor Wroe said that despite the findings, he expected debate would continue. ''There is still a lot we need to know,'' he said. ''But climate was the primary driver of the extinction of megafauna.''

 
SOURCE : http://www.theage.com.au/national/climate-the-culprit-in-megafaunas-demise-20130506-2j3j2.html
 


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