Thursday, December 02, 2010

Pizzly bears vs. grolar bears. Oh my!

There's only room for one of us bears in this town--One of nature’s great environmental battles, between two of the fiercest predators on the planet, may be playing out in the arctic, and one of those predators, the polar bear, could be the loser. As sea ice melts, the bears, which rely on the ice for hunting habitats, are moving south. As the climate warms, the grizzly is moving north. They are inevitably going to meet and will compete for survival. According to researchers at UCLA, the polar bears are likely to lose. Or, maybe not.

The UCLA researchers took an unusual approach. They constructed three-dimensional computer models of the skulls of polar bears and grizzlies, and simulated the process of biting. They wanted to see how hard the two species bite and how thick are their skulls. According to Graham Slater, a post-doc in ecology and evolutionary biology and the lead researcher at UCLA in the article published in PLoS ONE, a publication of the Public Library of Science, the two species can bite equally hard, but the polar bear’s skull “is a much weaker structure.”

This is crucial, he says, because that makes the polar bear less adaptable to the more plant-rich diet they will find as they move away from the sea.

"Chewing a lot of vegetables takes quite a lot of force to grind up," Slater said. "Grizzly bears are well suited to eating these kinds of food, but the polar bear is not well suited for it. The grizzly has a much more efficient skull for eating these kinds of foods,” he said. He did not add that in any fight, the grizzly would have an advantage if it goes for the head. But is that scenario real? Few dispute that polar bears are in trouble. Of the 19 populations of polar bears, only one is growing. Five are in decline, three appear stable and there is insufficient data on seven, most of the latter in Russia. Not only are the bears having trouble hunting—their main dish is seal—but some are drowning as they try to move from one piece of ice to another. They are strong swimmers but distances are growing and more bears are being seen in the high seas, threatened by wind and waves, parts of the ocean they would normally avoid. Fewer bears survive each year and there is fear some colonies—or all of them—will become extinct.

There has been a move to put them on the endangered species list. Skeptics point out—correctly—that there is not an overwhelming amount of data upon which to draw conclusions. Scientists in the north, and the people who live with the bears have a somewhat different view of the animals than do people in say Washington or Los Angeles.

Grizzlies now have been spotted in Manitoba, where they have not been seen in years. Grizzlies have even been seen on the ice in the far north of Canada. The two species are meeting and there have been at least two reports of a hybrid bear (one parent a polar, the other a grizzly), and in one case, a second generation hybrid, meaning they can reproduce. That is a nightmare animal if ever there is one. (Will we call them “pizzly bears” or “grolar bears?” )  In fact, polar bears descended from brown bears, around 150,000 years ago. That date is important because about 44,000 years ago there was a warm period and the polar bears apparently adapted and survived.

People who are suspicious of the extinction warnings think that is a good reason to calm down about the fate of the beautiful animals. Can the bears adapt again? We will see, won't we.

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