Death by a thousand cuts rather than some decisive ecological blow cost Alaska its fabulous woolly mammoths, according to new research published online this week in Nature Communications.
Those 10-foot-tall, hairy elephants that roamed the Beringian Steppes from Europe across Asia into North America slowly died out in response to climate change, shifting habitat and the spread of human populations, wrote geographer Glen MacDonald at the University of California Los Angeles and seven co-authors.
After thriving for almost 250,000 years in a world dominated by ice and wind-swept plains, the mammoths saw their world transform into a place with wetter ground, different plants and increasing numbers of ruthless hunters with weapons. By about 4,000 years ago, only remnant populations remained on Wrangel and St. Paul islands. They soon disappeared, too.
MacDonald and his team detail several reasons:
- Quick expansion of unpalatable birch shrub lands across the former steppe as the continental glaciers peeled back;
- Vast tracts of dry ground squishing into wet tundra with extensive bogs and peat wallows;
- The spread of spruce taiga and forest into the fringes.
The inexorable migration of humans into eastern Siberia and North America exerted even more pressure on the population by eliminating refuges from being hunted.
"Not one, but several factors would have made the present interglacial particularly challenging for woolly mammoths in Beringia," the scientists wrote here. "The relative importance of these specific forces may never be wholly resolvable, and was likely regionally variable, but combined, they provided the lethal intersection of factors to drive the woolly mammoths to extinction in continental Beringia with (relic) populations hanging on for several millennia on isolated Arctic islands."
The article, unlike many scientific pieces, is accessible to the public and contains many interesting charts that illustrate how Alaska's ice age icon disappeared.
"There was no one event that ended the mammoths," MacDonald told the Christian Science Monitor in a Live Science article that walks through the findings in detail and provides lots of great background links. "It was really the coalescence of climate change and the habitat change that triggered (it) -- and also human predators on the landscape at the end."
Sorting out the causes of mammoth extinctions — along with the disappearance of a menagerie of 40 other large mammal species at the end of the Ice Age — has long been one of paleontology's most interesting controversies.
One theory was once etched into the imaginations of school children: a wave of spear-chucking humans marched across the 1,000-mile-wide Bering Land Bridge from Asia as glaciers retreated and hunted down critters like mammoths and ancient bison during their sweep across the continent. The opposing viewpoint argued that it had to be climate change — the meltback of continental glaciers that raised sea levels and transformed an arid steppe into the wet Taiga and tundra of the current Far North. (Another intriguing explanation blamed an asteroid, making the loss of ice-age mammals a sequel of sorts to the extinction of dinosaurs.)
But over the past decade or so, a growing body of research (See this Nature article) has drawn on radiocarbon dating and genetic analysis to create a much more nuanced explanation.
In this new study, MacDonald and his team analyzed and compared the dates of 1,323 woolly mammoth remains with 658 dates showing the initiation of peat (when steppe morphed into tundra), 447 dates of the onset of trees and other wood growth, and 576 dates from prehistoric sites used by humans.
"We reconstruct the detailed pattern of extinction in Beringia, the last redoubt of the mammoths, and examine these various extinction hypotheses by comparing spatially and temporally the changes in mammoth populations relative to environmental changes over the past (45,000 years)," they explained.
To get a sense of the complexity of their work, check out these maps showing how mammoths yielded before the spread of peat, trees and people over tens of thousands of years.
As the millennia passed, mammoth habitat lacking significant populations of people got pushed further to the north and west.
"The geographic pattern of Beringian mammoth extinction, seems to be one of the final populations existing on the northern periphery of a once more extensive range," the authors wrote. "This pattern is consistent with the open vegetation available on the fringes of the continents and perhaps less intense human hunting there. As sea-level rose … some of these northern mammoth populations were isolated on what became Wrangel Island and the Pribilof Islands."
Those very last island-bound mammoths may have died out partly because they were a small isolated populations that couldn't weather the vagaries of bad winters or disease, or due to hunting by newly arrived humans.
The world of the mammoth, Alaska's official state fossil, finally ended with no bang, but a whisper of exhaled breath on some remote Arctic highland overlooking the sea.
"That final extinction of the island populations signalled the conclusion of the long sunset of the woolly mammoths in Beringia after over 20,000 years of multiple environmental challenges related to changes in climate, habitat and human predation," the authors concluded.
Contact Doug O'Harra at doug(at)alaskadispatch.com