"Long before it's in the papers"
June 13, 2012

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Causes of mammoth extinction resonate in modern realities, scientists say

June 13, 2012
Courtesy of University of California - Los Angeles
and World Science staff

Al­though hu­mans and woolly mam­moths co-existed for thou­sands of years, the shag­gy gi­ants dis­ap­peared 4,000 to 10,000 years ago—and sci­en­tists could­n’t ex­plain un­til re­cently quite why.

But new re­search sug­gests the last of the shag­gy beasts suc­cumbed to a com­bina­t­ion of cli­mate warm­ing, en­croach­ing hu­mans and hab­i­tat change—the same threats fac­ing many spe­cies to­day.

New re­search sug­gests the wool­ly mam­moths suc­cumbed to a com­bina­t­ion of cli­mate warm­ing, en­croach­ing hu­mans and hab­i­tat change—the same threats fac­ing many spe­cies to­day. (Im­age cour­tesy Berke­ley Nat'l Lab)
“The an­swer to why woolly mam­moths died off sounds a lot like what we ex­pect with fu­ture cli­mate warm­ing,” said one of the re­search­ers, Glen Mac­Don­ald, di­rec­tor of Uni­vers­ity of Cal­i­for­nia Los An­ge­les’ In­sti­tute of the En­vi­ron­ment and Sus­tain­abil­ity. The find­ings were pub­lished in a pa­per June 12 in the jour­nal Na­ture Com­mu­nica­t­ions.

By cre­at­ing what they called the most com­plete maps to date of all the changes hap­pen­ing thou­sands of years ago, the re­search­ers made a case that the ex­tinc­tion co­in­cid­ed with an ar­ray of creep­ing mis­for­tunes.

When the last ice age ended about 15,000 years ago, woolly mam­moths, mem­bers of the el­e­phant fam­i­ly, 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.

But 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.

The sce­nario laid out by Mac­Donald and col­leagues is as fol­lows. Though hu­mans had hunt­ed the 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. Af­ter a harsh, 1,500-year cold snap called the Young­er Dry­as about 13,000 years ago, the cli­mate be­gan to get even warm­er. This 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. Marshy peat­lands de­vel­oped, forc­ing the mam­moths to strug­gle through tough and nu­tri­tionally poor ter­rain. Forests be­came more abun­dant, squeez­ing mam­moths out of their form­er ter­ri­to­ry.

“Hunt­ing ex­pand­ed at the same time that the hab­i­tat be­came less amenable,” Mac­Don­ald said. Most of the woolly mam­moths died about 10,000 years ago, with fi­nal small popula­t­ions, liv­ing on is­lands, lin­ger­ing un­til about 4,000 years ago.

Many pre­vi­ous the­o­ries on the ex­tinc­tion tended to blame only one thing: hunt­ing, cli­mate changes, dis­ease or even a 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, a meth­od to de­ter­mine fos­sil ages, the re­search­ers traced the chang­ing loca­t­ions of peat­lands, forests, plant spe­cies, mam­moth popula­t­ions and hu­man set­tle­ments, and cross-referenced this in­forma­t­ion with cli­mate-change da­ta.

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Although humans and woolly mammoths co-existed for thousands of years, the shaggy giants disappeared 4,000 to 10,000 years ago—and scientists couldn’t explain until recently quite why. But new research suggests the last of the shaggy beasts succumbed to a combination of climate warming, encroaching humans and habitat change—the same threats facing many species today. “The answer to why woolly mammoths died off sounds a lot like what we expect with future climate warming,” said one of the researchers, Glen MacDonald, director of University of California Los Angeles’ Institute of the Environment and Sustainability. The findings were published in a paper June 12 in the journal Nature Communications. By creating what they called the most complete maps to date of all the changes happening thousands of years ago, the researchers made a case that the extinction coincided with an array of creeping misfortunes. When the last ice age ended about 15,000 years ago, woolly mammoths, members of the elephant family, 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. But 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 the Flintstonian behemoths 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. Marshy peatlands developed, forcing the mammoths to struggle through difficult and nutritionally poor terrain. Forests became more abundant, squeezing mammoths out of their former territory. “Hunting expanded at the same time that the habitat became less amenable,” MacDonald said. Most of the woolly mammoths died about 10,000 years ago, with final small populations, living on islands, lingering until about 4,000 years ago. Many previous theories on the extinction tended to blame only one thing: hunting, climate changes, disease or even a 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, a method to determine fossil ages, the researchers traced the changing locations of peatlands, forests, plant species, mammoth populations and human settlements, and cross-referenced this information with climate-change data.