Brown bears better adapted to warming Arctic, scientists say

What’s for supper? This polar bear would probably prefer a tasty seal pup— because the skulls and teeth of polar bears are specially adapted to this easy-to-eat food. (PHOTO BY JANE GEORGE)

The polar bear is the only living bear that eats only a diet of meat, having evolved to Arctic conditions less than a million years ago from the I’ll-eat-anything brown bear.

So, now there’s increasing attention from researchers on what polar bears will eat when their supply of seal pups decreases along with the sea ice.

If Arctic warming continues, one recent study predicts polar bears may turn to snow goose eggs to fill their bellies.

Another study, published Nov. 5 on an on-line research journal called Plos one, says polar bears may be at a disadvantage precisely because they adapted to this diet of seals.

The polar bear evolved smaller molars and a low, slender skull which allow it to “efficiently process” seal flesh and blubber.

But if polar bears can’t find enough of their favorite foods, they may suffer from competition with northward moving brown bear populations for resources that they are “ill-equipped” to use, say the authors of a paper that looks at the consequences of rapid evolution in polar bears.

Their research shows an “extremely rapid evolution” of brown bears into polar bears which produced a skull which is less suited to processing tough, hard-to chew diets with lots of vegetation.

Although the heads and muscle-power of two species are similar, tests reveal the polar bear’s skull is a “weaker, less work-efficient structure,” and does not appear well suited to large amounts of chewing, the study’s authors say.

Compared with other bears, polar bears have low flat skulls with high-sitting eyes, which likely developed as an advantage so they could thrust their heads into breathing holes or pupping dens. Because polar bears feed almost exclusively on young ringed and bearded seals, they don’t need as large skulls as in as lions or wolves that regularly eat prey larger than themselves, the study says.

And they also lack the well-developed “blade-like” teeth because polar bears feed almost exclusively on blubber and flesh. These, unlike bone, require little or no chewing or tearing prior to swallowing, the study notes.

Brown bears eat animals when available, but they also eat large amounts of plants in the summer, including grasses which require a lot of work before they can be swallowed.

So, increased competition from brown bears expanding their range northward is likely to present “a significant challenge” to polar bears, the study concludes, pointing to areas where Arctic foxes overlap with red foxes, which end up controlling prime feeding and denning areas.

Brown bears may have the upper hand as the Arctic warms, and the polar bear, which the study calls one of the most striking examples of rapid evolution, “may be lost as quickly as it appeared.”