Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, California, United States of America.
PLoS One. 2010 Nov 5;5(11):e13870. doi: 10.1371/journal.pone.0013870.
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.
北极熊是唯一一种完全以肉食为食的熊科动物。尽管有大量有案可稽的颅面结构适应海豹肉和鲸脂的饮食，但分子和古生物学数据表明，这种形态独特的物种在不到一百万年的时间里，从杂食性的棕熊进化而来。为了更好地了解这种饮食特化的进化，我们使用系统发育测试来估计北极熊形态特化的速度。然后，我们使用有限元分析（FEA）比较了北极熊头骨的进食性能极限与亲缘关系和地理上相近的棕熊的进食性能极限。结果表明，北极熊谱系中半水生适应和饮食特化的极其快速进化产生了一种颅骨形态，其强度弱于棕熊，不太适合处理坚韧的杂食或草食性食物。我们的研究结果表明，当前气候趋势的持续发展不仅会通过消灭北极熊的主要食物来源来影响它们，还会通过与向北推进的、广泛分布的棕熊种群竞争资源，使它们无法利用这些资源，从而对北极熊产生影响。
