| Summary: | Top predators play a crucial role in defining the structure and functioning of ecosystems. In the Arctic, polar bears (Ursus maritimus ) feed on marine mammal prey over vast geographic ranges and patterns in their foraging habits may reflect ecological variability over multiple temporal and spatial scales. In this study I used fatty acid (FA) signature analysis to generate detailed estimates of polar bear diets and to qualitatively examine the foraging patterns of several species of arctic marine mammals. Seasonal and sex differences in the lipid content of polar bear fat reflected the physiological demands of seasonal fasts and sex-specific differences in reproductive costs. The FA composition of the polar bear's primary prey, ringed seals (Phoca hispida), revealed spatial, temporal, and demographic differences in foraging that were consistent with the generalist feeding habits of ringed seals. FA signatures of ringed seals, harbour seals (P. vitulina), harp seals (Pagophilus groenlandica), hooded seals (Cystophora cristata), bearded seals ( Erignathus barbatus), beluga whales (Delphinapterus leucas ), narwhals (Monodon monoceros), and walruses ( Odobenus rosmarus) differed between and within species. FA data were consistent with taxonomic and ecological relationships between species and provided a foundation for a detailed examination of polar bear foraging. Using quantitative FA signature analysis (QFASA), I generated diet estimates for polar bears (n = 1902) in 10 Canadian subpopulations. In most areas, diets were dominated by ringed seals, but in the eastern Arctic, by harp seals. Polar bear foraging was most similar among neighboring population zones with similar prey assemblages, but also differed geographically within several regions. Large prey such as bearded seals and walruses were generally consumed most often by large male bears, while ringed seals and harbour seals were most important to females and juveniles. Polar bear diets differed interannually, especially in Western Hudson Bay and Davis Strait, apparently in response to bottom-up food web effects. Overall, this study suggests a complex relationship between sea ice conditions, prey population dynamics, and polar bear foraging. QFASA estimates of polar bear diets were consistent with known life-history patterns and these results establish an important baseline for detecting future changes in arctic marine ecosystems. Thesis (Ph.D.)--Dalhousie University (Canada), 2006.
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