Modelling Future Impacts of Climate Change and Harvest on the Reproductive Success of Female Polar Bears (Ursus maritimus)

  • Author / Creator
    Péter Kálmán Molnár
  • Climate change and human harvest are among the most significant threats to polar
    bear (Ursus maritimus) populations today. Climatic warming and resultant sea ice
    reductions affect polar bears because they depend on this substrate for most aspects of
    their life history, including access to seals, their main prey. Harvest is highly
    sex-selective, and males have been reduced significantly in most Canadian populations,
    leading to concerns that males might eventually be depleted to a point where many
    females become unable to mate (a so-called Allee effect). Few studies have attempted
    quantitative predictions of polar bear population dynamics under climate change, and all
    predictions are associated with large uncertainty. The conditions that would lead to an
    Allee effect are similarly unclear, but sex-selective harvest is ongoing. In this thesis I
    coupled mathematical models with empirical data to understand and anticipate effects of
    climate change and human harvest on the reproductive success of female polar bears. To
    predict conditions leading to an Allee effect, I developed a mechanistic model for the
    polar bear mating system. The model described observed mating dynamics well, predicts
    the proportion of mated females from population density and operational sex ratio, and
    specifically outlines conditions for an Allee effect. Female mating success was shown to
    be a nonlinear function of the operational sex ratio, implying sudden reproductive
    collapse if males are severely depleted. The threshold operational sex ratio for such an
    Allee effect depends on population density. To predict effects of climatic warming on
    female reproduction, I first developed a body composition model that estimates the
    amount of energy stored in the fat and protein reserves of a polar bear. Based on this
    model, I developed a dynamic energy budget model that predicts changes in energy stores
    of both fasting and feeding adults. Metabolic rates of adult polar bears were estimated
    using the energy budget model, and corresponded closely to theoretically expected and
    experimentally measured values. The models were then used to predict changes in litter
    size of pregnant females in western Hudson Bay as a result of predicted losses in sea ice
    and feeding opportunities, and consequent reductions in female storage energy. Severe
    declines in litter size can be expected under climatic warming, although the precise rates
    of change depend on current, to date unobserved, summer feeding rates. Behavioural
    adaptation towards terrestrial feeding is unlikely to significantly compensate for expected
    losses in storage energy and resultant reductions in litter size. The results of this thesis are
    a significant step towards a predictive framework for polar bear populations, and aid
    optimal population management and proactive direction of conservation efforts.

  • Graduation date
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • 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
  • Institution
    University of Alberta
  • Degree level
  • Specialization
    • Mathematical and Statistical Biology