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

  2009

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-wszm-8d62

• 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.