Climate, habitat, humans 'in cahoots to kill mammoths'

Rising temperatures, changing vegetation and the spread of humans all contributed to the extinction of the woolly mammoth, according to a new study that said no single factor was to blame. The tusked mammal's demise was gradual, not sudden, said the authors, disputing earlier assertions that the giants were wiped out quickly -- either by disease, humans or a catastrophic weather event. "It wasn't just one thing that took them out everywhere all at once," author Glen MacDonald of the University of California's department of evolutionary biology told AFP. "With the mammoths, it was just a story of this almost continuous litany of challenges that they faced in terms of changing climate, huge changes in habitat and then the spread of humans and potentially human predation to new areas." The cause of the woolly beasts' disappearance has generated fierce debate among experts. Some hold that the giants that once strode across Eurasia and north America were hunted to extinction by humans, while others blame global warming for decimating a species adapted for colder climes. A colony of woolly mammoths is believed to have survived up to about 4,000 years ago on what is today Russia's Wrangel Island, north of Siberia in the Arctic Ocean. In a paper published Tuesday in Nature Communications, a team of researchers in the United States and Russia said their own analysis of radiocarbon-dated evidence has revealed a pattern of slow demise caused by several factors. "This is an extinction that took a long time. It extended over thousands of years," said MacDonald. The team asserts that woolly mammoths were abundant up to 45,000 to 30,000 years ago in continental Beringia, a land bridge that linked present-day Alaska and eastern Siberia before it was submerged by the sea thousands of years ago. In the last Ice Age, about 25,000 to 20,000 years ago, northern populations declined while those in the south increased, they said. "Coming out of that, though, you had smaller populations that were just beginning to grow -- and they were then faced with large habitat changes that made the south no longer an amenable area for them and started threatening their ability to utilise the north," said MacDonald. The problem lay in the spread of peat- and wetland areas which offered poor mammoth nutrition, he explained. The giants ate grasses and the soft shoots of woody plants like willows, and this food became increasingly scarce. "At the same time, for the first time in Alaska and North America they had human predators there as well," pointed out MacDonald. This type of coalescence of factors may be seen again in the near future, he warned. "If you look at the magnitude of changes we anticipate with climate change in this upcoming century and land use changes with human population growth and land cover changes, we are kind of subjecting species to a lot of the same pressures but we are compressing the timescale," said the scientist. "That is frightening in some ways."