Rumble in the Tundra: Polar Bears vs. Grizzlies

In a report that could have been created by the producers of Shark Week, evolutionary biologists have concluded that grizzly bears will outcompete polar bears as climate change pushes them together in rapidly shrinking habitat.  Published in the Public Library of Science, the study, entitled "Biomechanical Consequences of Rapid Evolution in the Polar Bear Lineage," examined the development of the jaws of polar bears and concluded that low-slender skulls and reduced surface area of their grinding molar teeth would make polar bear unable to thrive in habitat where they were forced into an omnivorous diet.  

The image below shows the difference between polar bear and brown bear biting capacities by mapping von Mises stresses.  The polar bear is shown on the left and the brown bear on the right. 


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Polar bears are the only fully carniverous bear, and the unique structure of their skull and teeth make them ill-prepared to start incorporating plants into their diet. This evolutionary disadvantage will give grizzlies the upper-hand as the two species move into habitats with limited food sources. The result will be an increasing speed of extinction for the polar bear subspecies.  

Grizzly bears are moving northward while polar bears are moving southward into Canada as their habitat disappears. Scientists estimate there are about 20,000-25,000 polar bears alive today.  Polar bears find most of their food on barren sea ice, in between the months of April and July.  During the rest of the year, when they are stranded on land, they fast for long periods of time, as long as four months at a time.  In the Southern range of polar bears, the sea ice has been melting earlier in the Spring and forming later in the Fall.  

The research is another sign of how the world is adapting to rapidly rising temperatures.
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Adam Werbach is the co-founder of sharing startup Yerdle, formerly the chief sustainability officer for Saatchi & Saatchi and the president of the Sierra Club. He is the author of Strategy for Sustainability: A Business ManifestoHe lives in San Francisco and Bolinas, California.

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