Modelling Future Impacts of Climate Change and Harvest on the Reproductive Success of Female Polar Bears (Ursus maritimus) 
Creators: Péter Kálmán Molnár
Publisher: name: University of Alberta Library
Year: 2009

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