Journal
OIKOS
Volume 120, Issue 10, Pages 1469-1478Publisher
WILEY
DOI: 10.1111/j.1600-0706.2011.19277.x
Keywords
-
Categories
Funding
- Natural Sciences and Engineering Research Council (NSERC)
- Killam Trusts
- Polar Continental Shelf Project
- Canadian Wildlife Service
- Northern Scientific Training Program
- Dr. Patrick Lett Student Bursary Fund
- Government of Nunavut, Nunavut Wildlife Management Board
- Fisheries and Oceans Canada
- Churchill Northern Studies Centre
- Ontario Ministry of Natural Resources
- Nunavut Dept of Environment
- Makivik Corporation
- Ontario Parks
- Safari Club International (Ontario and Detroit Chapters)
- Les Brasseurs du Nord
- La Fondation de la Faune du Quebec
- La Societe de la faune et des parcs du Quebec
- OMNR's Climate Change Program [CC-03/04-010]
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The cumulative effect of individual-level foraging patterns may have important consequences for ecosystem functioning, population dynamics and conservation. Dietary specialization, whereby an individual exploits a subset of resources available to the rest of the population, can develop in response to environmental or intrinsic population factors. However, accurate assessment of individual diets may be difficult because analyses of recent food intake may misrepresent foraging variability within a heterogeneous environment. We used quantitative fatty acid signature analysis (QFASA) and a novel index of longitudinal dietary change to examine the individual foraging patterns of 64 polar bears Ursus maritimus successively sampled in Western and Southern Hudson Bay between 1994-2003. Estimated diets varied between and within age and sex classes, with adult male polar bears consuming significantly more bearded seal Erignathus barbatus than adult female or subadult bears, whose diets were dominated by ringed seal Pusa hispida. Among individual adult males, consumption of bearded seal accounted for 0-98% of the diet and bearded seal consumption was positively correlated with individual dietary specialization, as measured by proportional similarity (PSi) to the rest of the population. Most individual diets were consistent from year-to-year and were therefore not a product of short-term heterogeneity in prey distribution. However, a novel dietary change index indicated that adult male polar bears had the most temporally variable diets with 23% of adult males switching their diet from predominantly ringed seal to predominantly bearded seal or vice versa. We conclude that QFASA is well-suited to analyses of individual-level foraging because it reflects an animal's diet over the preceding weeks to months. The subpopulations of bears in this study were near the southern limit of their species range and have experienced negative individual-and population-level impacts related to sea ice loss and climate warming. The tightly constrained diets of some individuals, particularly adult females and subadults, may make them especially sensitive to future climate change.
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