Polar Bears Unlikely to Survive in Warmer World, Biologists Say
ScienceDaily (Nov. 24, 2010) — Will polar bears survive in a warmer world? UCLA life scientists present new evidence that their numbers are likely to dwindle.
Climate change will force polar bears south, where they are unsuited for the diet. (Credit: Alan D. Wilson)
As polar bears lose habitat due to global warming, these biologists say, they will be forced southward in search of alternative sources of food, where they will increasingly come into competition with grizzly bears.
To test how this competition might unfold, the UCLA biologists constructed three-dimensional computer models of the skulls of polar bears and grizzly bears -- a subspecies of brown bears -- and simulated the process of biting. The models enabled them to compare the two species in terms of how hard they can bite and how strong their skulls are.
"What we found was striking," said Graham Slater, a National Science Foundation-funded UCLA postdoctoral scholar in ecology and evolutionary biology and lead author of the research. "The polar bear and brown bear can bite equally hard, but the polar bear's skull is a much weaker structure."
The implication is that polar bears are likely to lose out in competition for food to grizzlies as warmer temperatures bring them into the same environments, because grizzlies' stronger skulls are better suited to a plant-rich diet, said Slater and Blaire Van Valkenburgh, UCLA professor of ecology and evolutionary biology and senior author of the research.
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Biomechanical Consequences of Rapid Evolution in the Polar Bear Lineage
Graham J. Slater1*, Borja Figueirido2, Leeann Louis3, Paul Yang1, Blaire Van Valkenburgh1
1 Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, California, United States of America, 2 Departamento de Ecología y Geología, Área de Paleontología, Facultad de Ciencias, Universidad de Málaga, Campus Universitario de Teatinos, Málaga, Spain, 3Cornell University Museum of Vertebrates, Ithaca, New York, United States of America
Abstract
The polar bear is the only living ursid with a fully carnivorous diet. Despite a number of well-documented craniodental adaptations for a diet of seal flesh and blubber, molecular and paleontological data indicate that this morphologically distinct species evolved less than a million years ago from the omnivorous brown bear. To better understand the evolution of this dietary specialization, we used phylogenetic tests to estimate the rate of morphological specialization in polar bears. We then used finite element analysis (FEA) to compare the limits of feeding performance in the polar bear skull to that of the phylogenetically and geographically close brown bear. Results indicate that extremely rapid evolution of semi-aquatic adaptations and dietary specialization in the polar bear lineage produced a cranial morphology that is weaker than that of brown bears and less suited to processing tough omnivorous or herbivorous diets. Our results suggest that continuation of current climate trends could affect polar bears by not only eliminating their primary food source, but also through competition with northward advancing, generalized brown populations for resources that they are ill-equipped to utilize.
Citation: Slater GJ, Figueirido B, Louis L, Yang P, Van Valkenburgh B (2010) Biomechanical Consequences of Rapid Evolution in the Polar Bear Lineage. PLoS ONE 5(11): e13870. doi:10.1371/journal.pone.0013870
Editor: Andrew Allen Farke, Raymond M. Alf Museum of Paleontology, United States of America
Received: July 2, 2010; Accepted: October 18, 2010; Published: November 5, 2010
Copyright: © 2010 Slater et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: The work was funded by the National Science Foundation (http://www.nsf.gov/) NSF 0709792, 0517748; Ministerio de Cinencia E Innovacion (http://www.micinn.es/portal/site/MICINN/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
* E-mail: gslater@ucla.edu
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