Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada.
Integr Comp Biol. 2004 Apr;44(2):163-76. doi: 10.1093/icb/44.2.163.
Polar bears (Ursus maritimus) live throughout the ice-covered waters of the circumpolar Arctic, particularly in near shore annual ice over the continental shelf where biological productivity is highest. However, to a large degree under scenarios predicted by climate change models, these preferred sea ice habitats will be substantially altered. Spatial and temporal sea ice changes will lead to shifts in trophic interactions involving polar bears through reduced availability and abundance of their main prey: seals. In the short term, climatic warming may improve bear and seal habitats in higher latitudes over continental shelves if currently thick multiyear ice is replaced by annual ice with more leads, making it more suitable for seals. A cascade of impacts beginning with reduced sea ice will be manifested in reduced adipose stores leading to lowered reproductive rates because females will have less fat to invest in cubs during the winter fast. Non-pregnant bears may have to fast on land or offshore on the remaining multiyear ice through progressively longer periods of open water while they await freeze-up and a return to hunting seals. As sea ice thins, and becomes more fractured and labile, it is likely to move more in response to winds and currents so that polar bears will need to walk or swim more and thus use greater amounts of energy to maintain contact with the remaining preferred habitats. The effects of climate change are likely to show large geographic, temporal and even individual differences and be highly variable, making it difficult to develop adequate monitoring and research programs. All ursids show behavioural plasticity but given the rapid pace of ecological change in the Arctic, the long generation time, and the highly specialised nature of polar bears, it is unlikely that polar bears will survive as a species if the sea ice disappears completely as has been predicted by some.
北极熊（Ursus maritimus）生活在环极北极的冰覆盖水域中，特别是在大陆架上的近岸年度冰区，那里的生物生产力最高。然而，在很大程度上，根据气候变化模型预测的情况，这些首选的海冰栖息地将发生重大变化。空间和时间上的海冰变化将通过减少其主要猎物海豹的可用性和数量，导致涉及北极熊的营养相互作用发生转变。在短期内，如果目前厚厚的多年冰被具有更多冰隙的年度冰所取代，气候变暖可能会改善大陆架上高纬度地区的熊和海豹栖息地，因为这更适合海豹生存。从减少海冰开始的一系列影响将表现为脂肪储存减少，导致繁殖率降低，因为雌性在冬季禁食期间将减少投资于幼崽的脂肪。没有怀孕的熊可能不得不通过越来越长的无冰期在陆地上或剩余的多年冰上禁食，同时等待重新冻结和返回捕猎海豹。随着海冰变薄，变得更加破碎和不稳定，它可能会更多地响应风和水流移动，因此北极熊需要走或游泳更多，从而消耗更多的能量来保持与剩余的首选栖息地的联系。气候变化的影响可能表现出很大的地理、时间甚至个体差异，并且非常多变，这使得很难制定出足够的监测和研究计划。所有的熊科动物都表现出行为可塑性，但考虑到北极地区生态变化的快速步伐、较长的世代时间以及北极熊高度专业化的性质，如果像一些预测那样，海冰完全消失，北极熊作为一个物种生存的可能性很小。
