December 15, 2010

Interbreeding, Not Habitat Loss, Biggest Danger To Polar Bears

Polar bears may be able to survive the damage done to their native habitats due to greenhouse gas emissions, oil, and pollution, only to die out due to inter-species mating, scientists reported in two separate studies Wednesday.

The iconic Arctic bears, which were originally added to the threatened species list in 2008 because of the effect of global warming on the ice-covered environments they call home, could continue to survive and thrive if stricter limits are placed on the emissions that threaten their habitats, researchers from the U.S. Geological Survey and the University of Washington (UW) wrote in the December 16 issue of the journal Nature.

Projections made by the organization in 2007 were "based solely on the business-as-usual greenhouse gas scenario," Steven Amstrup, an emeritus researcher with the U.S. Geological Survey, said in a statement Wednesday.

Those statistics said that two-thirds of the world's 22,000 polar bears could be wiped out due to melting ice in the Arctic region, and while Amstrup said that it was "a pretty dire outlook," he added that it "didn't consider the possibility of greenhouse gas mitigation."

The new model cited in the Nature report was based on the work of UW Associate Professor of Atmospheric Sciences Cecilia Bitz, and according to a university press release, "indicates there is no 'tipping point' that would result in unstoppable loss of summer sea ice when greenhouse gas-driven warming rose above a certain threshold."

Bitz said that the findings provided "a very promising, hopeful message" but were also "an incentive for mitigating greenhouse emissions."

Similarly, climate models completed by Stephanie Pfirman, an environmental scientist at Columbia University's Lamont-Doherty Earth Observatory in New York, and colleagues showed that sea ice would continue to accumulate on the northern side of the Canadian Arctic Archipelago and Greenland.

However, the study--which was the subject of a December 15 article by Nature News writer Nicola Jones--points out that polar bears continue to face other threats, ranging "from oil spills and other pollution to extinction through cross-breeding between distinct animal populations."

According to Jones, the changes in habitat brought about by global climate change have brought polar bears into contact with grizzly bears, leading to cross-breeding and the formation of hybrids identified by AFP as 'pizzly' bears. The first of these 'pizzlies' was discovered by scientists in 2006, the French news agency reported, while another bear species with mixed DNA was discovered earlier this year.

The bears aren't the only species being affected, according to AFP. Whales from the Atlantic and Pacific have also come into contact with one another, leaking to the risk of intermingling. Furthermore, the media outlet quotes biologists writing in Nature as noting that "as more isolated populations and species come into contact, they will mate, hybrids will form, and rare species are likely to go extinct."

In light of those discoveries, Amstrup said that there is "still a fairly high probability" that polar bears in the various Arctic ecosystems "could disappear"¦ but with mitigation and aggressive management of hunting and other direct bear-human interactions, the probability of extinction would now be lower than the probability that polar bear numbers will simply be reduced."


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