Brown bruins could displace polar bears, scientists say

Scientists are warning that polar bears, which evolved quickly to dine mainly on seals (left), could face formidable competition as brown bears expand northward with global warming.

The iconic white bruins exist almost entirely on a meat diet, while their omnivorous southern cousins will chow down on almost any animal flesh and gorge themselves on berries.

In fact, one recent study predicts that polar bears may be forced to eat the eggs of snow geese (right) to fill their bellies.

Another study, published Nov. 5 on an online research journal called PLoS One, says polar bears may be at a disadvantage precisely because they have adapted over the past million years to a diet of seals.

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

Another paper that examined the "extremely rapid evolution" of polar bears notes that their skulls are 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 large skulls like lions or wolves, which regularly eat prey larger than themselves, the study says.

And polar bears also lack the well-developed "blade-like" teeth because they 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 southern red foxes, which end up controlling prime feeding and denning areas.


Source:
The Province, "Brown bruins could displace polar bears, scientists say", accessed November 9, 2010