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Forum: Stones Forum
Moderated by : Andy B , TimPrevett , coldrum , Klingon , MickM , TheCaptain , bat400 , davidmorgan , Runemage , SolarMegalith , sem
Respond to: What, or who, killed the last mammoths?
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bat400
Joined:
10-04-2006
Messages: 1349
from South Central Indiana, US
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|  New Message Posted!2012-07-01 23:25
Woolly mammoth extinction has lessons for modern climate change
Although humans and woolly mammoths co-existed for millennia, the shaggy giants disappeared from the globe between 4,000 and 10,000 years ago, and scientists couldn't explain until recently exactly how the Flinstonian behemoths went extinct.
In a paper published June 12 in the journal Nature Communications, UCLA researchers and colleagues reveal that not long after the last ice age, the last woolly mammoths succumbed to a lethal combination of climate warming, encroaching humans and habitat change — the same threats facing many species today.
"We were interested to know what happened to this species during the climate warming at the end of the last ice age because we were looking for insights into what might happen today due to human-induced climate change," said Glen MacDonald, director of UCLA's Institute of the Environment and Sustainability (IoES).
MacDonald, a professor of geography and of ecology and evolutionary biology, worked with UCLA IoES scientists Robert Wayne and Blaire Van Valkenburgh, UCLA geographer Konstantine Kremenetski, and researchers from UC Santa Cruz, the Russian Academy of Science and the University of Hawaii Manoa.
Their work shows that although hunting by people may have contributed to the demise of woolly mammoths, contact with humans isn't the only reason this furry branch of the Elephantidae family went extinct. By creating the most complete maps to date of all the changes happening thousands of years ago, the researchers showed that the extinction didn't line up with any single change but with the combination of several new pressures on woolly mammoths.
When the last ice age ended about 15,000 years ago, woolly mammoths were on the rise. Warming melted glaciers, but the still-chilly temperatures were downright comfy for such furry animals and kept plant life in just the right balance. It was good weather for growing mammoths' preferred foods, while still too cold for the development of thick forests to block their paths or for marshy peatlands to slow their stride.
But the research explains that the end was coming for the last of the woolly mammoths, who inhabited Beringia, a chilly region linked by the Bering Strait that included wide swaths of Alaska, the Yukon and Siberia. Though humans had hunted woolly mammoths in Siberia for millennia, it wasn't until the last ice age that people crossed the Bering Strait and began hunting them in Alaska and the Yukon for the first time. After a harsh, 1,500-year cold snap called the Younger Dryas about 13,000 years ago, the climate began to get even warmer. The rising temperatures led to a decline in woolly mammoths' favored foods, like grasses and willows, and encouraged the growth of low-nutrient conifers and potentially toxic birch.
"It's not just the climate change that killed them off," MacDonald said. "It's the habitat change and human pressure. Hunting expanded at the same time that the habitat became less amenable."
Many previous theories about the mammoths' extinction tended to blame only one thing: hunting, climate changes, disease or even an ice-melting, climate-changing meteor, MacDonald said. The new research marks the first time scientists mapped out and dated so many different aspects of the era at once. Using radiocarbon dating of fossils, the researchers were able to trace the changing locations of peatlands, forests, plant species, mammoth populations and human settlements over time, and they cross-referenced this information with climate-change data.
The research used 1,323 mammoth radiocarbon dates, 658 peatland dates, 447 tree dates, and 576 dates from Paleolithic archaeological sites. Scientists from IoES and other UCLA departments obtained samples and worked on radiocarbon dating of the peatlands and the forests, and they created a database uniting information on hundreds of previously dated mammoth samples, developing the final map from thousands of dates and latitude and longitude records.
"We are, in a sense, time-traveling with our maps to look at the mammoths," he said.
Thanks to coldrum for the link. For more, see http://phys.org/news/2012-06-climate-habitat-humans-cahoots-mammoths.html.
Woolly mammoth extinction has lessons for modern climate change
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bat400
Joined:
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from South Central Indiana, US
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| New Message Posted!2010-04-20 04:46
Submitted by coldrum ---
The last known population of woolly mammoths, roaming a remote Arctic island long after humans invented writing, were wiped out quickly, reports a study released Wednesday.
The culprit might have been disease, humans or a catastrophic weather event, but was almost certainly not climate change, suggests the study, published in the Proceedings of the Royal Society B.
Exactly why a majority of the huge tuskers that once strode in large herds across Eurasia and north America died out toward the end of the last ice age has generated fiery debate.
Some experts hold that mammoths were hunted to extinction beginning some 10,000 years ago by the species that was to become the planet's dominant predator -- humans.
Others argue that climate change was more to blame, leaving a species adapted for frigid climes ill-equipped to cope with a warming world.
It has long been known that a colony of woolly mammoths survived up until about four thousand years ago on what is today Russia's Wrangel Island, north of Siberia in the Arctic Ocean.
Radiocarbon dating shows that at least a few hardy individuals were still hanging on as late as 1700 B.C.
To better understand their demise, researchers led by Anders Angerbjorn of Stockholm University analysed bits of mitochondrial DNA -- genetic material inherited through females -- extracted from bone and tusk.
They reasoned that signs of dwindling genetic diversity would mean that too much inbreeding among a small population could have partially caused the animals to die out.
"It could be that the island was simply too small to support a long-term viable mammoth population," the authors speculated.
About 7,600 square kilometres (2,900 square miles) in area, Wrangel Island is a bit smaller than Corsica or Puerto Rico.
Once connected to the mainland by an ice bridge, Wrangel was gradually cut off by water 12,000 to 9,000 years ago.
A loss of genetic variation could also have resulted from the shift in climate as Earth entered the so-called interglacial period, a boon for many animals, but not for the giant tuskers, the study said.
To their surprise, however, the researchers found that genetic diversity remained stable, and even increased slightly, right up to the bitter end.
"This suggests that the final extinction was caused by a relatively sudden, rather than gradual, change in the mammoths' environment," the study said.
Humans appear to have arrived on the island about 100 years after the huge mammals had vanished, according to archeological data.
This would exculpate homo sapiens from killing off the last mammoths, though it is possible humans arrived earlier but left no trace.
The fate of mammoths on Wrangel Island, they caution, is not necessarily a microcosm for the species as a whole because islands exert unique evolutionary pressures on animal species.
One theory is that expanding forests in Europe and parts of Asia robbed the grass-eating mammoths of their preferred habitat, gradually starving them to death.
For more, including genetic testing for changing diversity, see http://news.yahoo.com/s/afp/20100331/ts_afp/sciencearchaeologymammothgenetics
[ This message was edited by: bat400 on 2010-04-20 04:47 ]
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