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Polar bear (Ursus maritimus) foraging ecology in spring

  • Author / Creator
    Pilfold, Nicholas W
  • Polar bears (Ursus maritimus) enter a period of intensified feeding in the spring, which allows for the accumulation of energy stores critical to surviving the open water season. Study on polar bear predation has been limited by sample size and spatial extent, and hypotheses on the demographic composition of seal kills and the spatial distribution of polar bears and seals were incongruent. In this thesis, I used a long-term dataset (1985-2011) of seals killed by polar bears (n = 650) and predation attempts at ringed seal (Pusa hispida) subnivean lairs (n = 1396) in the Beaufort Sea, Canada, to link the habitats polar bears use and the seals that polar bears kill during hyperphagia. Using DNA and field observations, I determined that polar bears primarily killed ringed seals, but that bearded seals (Erignathus barbatus) contributed a significant portion of kill biomass. An increase in seal kill frequency was observed temporally over the spring, associated with the onset of ringed seal whelping. The influence of ringed seal whelping was also observable at inter-annual scales, with total kill frequency positively correlated to years of high ringed seal natality, while adults were killed in higher proportion in years when natality was low. Employing locations of seal kills and attempted hunts at ringed seal subnivean lairs, I examined the habitats in which polar bears hunt and ringed seals whelp. Polar bears selected for active areas of sea ice near the floe edge when hunting seals. Ringed seal whelping areas were located over a range of habitats, and the distribution was correlated with natality. In years of low natality pup kills were observed primarily in shorefast ice close to land, but during years of high natality the distribution widened, and pup kills were observed farther from land and more frequently near active ice areas. Results suggest that during periods of high natality, the habitats in which ringed seals whelp overlaps with areas preferred by polar bears for hunting. The spatial overlap between polar bears and whelping ringed seals likely influences a change in the age-class proportions of kills, as polar bears respond to the availability of vulnerable pups. Finally, I explored the assumptions of common analytical modelling approaches in ecology. I established that including biologically relevant measures, such as the size of kills, provided significant improvement to the models in both fit and interpretation. Measuring only the occurrence of an ecological event, whether temporally or spatially, was found to be insufficient when validated against independent data. The empirical analyses within this dissertation suggest that strong assumptions of ecological models may not always hold. Collecting biologically relevant data in the field, beyond simply recording events, can test model assumptions and validate results, increasing model portability and the relevance of the findings.

  • Subjects / Keywords
  • Graduation date
    2015-06
  • Type of Item
    Thesis
  • Degree
    Doctor of Philosophy
  • DOI
    https://doi.org/10.7939/R38W9Q
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
    English
  • Institution
    University of Alberta
  • Degree level
    Doctoral
  • Department
    • Department of Biological Sciences
  • Specialization
    • Ecology
  • Supervisor / co-supervisor and their department(s)
    • Derocher, Andrew E (Biological Sciences)
  • Examining committee members and their departments
    • Trites, Andrew (University of British Columbia)
    • Stirling, Ian (Biological Sciences)
    • Boyce, Mark (Biological Sciences)
    • Bayne, Erin (Biological Sciences)