Estimating Effective Sizes of Canada’s Polar Bear Populations

• Main Author: Wainwright, Hayden
• Other Authors: Lougheed, Stephen, Biology
• Format: Thesis
• Language: English
• Published: 2022
• Subjects: Conservation Biology; Effective population size; Polar bear; Arctic; Hudson Bay; Hudson; Arctic Archipelago; Ursus maritimus
• Online Access: http://hdl.handle.net/1974/30062

Arctic climate continues to warm more rapidly than the rest of the planet, and species distributions are expected to change profoundly. As the Arctic’s apex predator, the polar bear (Ursus maritimus) is greatly impacted by many aspects of the changing Arctic environment. We do not have a clear understanding of polar bear population structure and estimates of important demographic parameters are out of date or lacking for many populations. Effective population size (Ne) is an important metric when addressing the persistence of a species and is proportional to the level of genetic diversity within a population. My study uses fecal, harvest tissue, and biopsy samples to explore estimators of Ne and to investigate the contemporary and historic trends in Ne for the Canadian Arctic populations of polar bears. My results suggest that the linkage disequilibrium method of estimating contemporary Ne is most appropriate for monitoring projects that uses non-invasively collected, or degraded samples as this method can produce precise estimates of Ne with only 322 SNPs. Contemporary estimates of Ne and corresponding ratios of effective to census size (Ne/Nc) for four previously defined genetic clusters are: Polar Basin (Ne=145, Ne/Nc=0.07), Arctic Archipelago (Ne=360, Ne/Nc=0.04), M’Clintock Channel (Ne=149, Ne/Nc=0.21), and the Hudson Bay Complex (Ne=307, Ne/Nc=0.07). Given recent evidence of migration between M’Clintock Channel and the Arctic Archipelago, I suggest that conservation efforts focus on the Hudson Bay Complex and Polar Basin regions due to their low connectivity with other clusters and their low effective sizes. My analysis of historic demographic trends suggests the four genetic cluster within the Canadian Arctic have independently experienced declines in effective size over the last 500 Ky, with only slight periods of recovery during times of global cooling. These results indicate current estimates of Ne likely represent a historic low in Ne and therefore an already reduce level of genetic diversity. Future studies should aim to better understand the dynamics between the Arctic Archipelago and M’Clintock Channel as the connectivity between these regions is likely to be vital for the long-term persistence of the polar bear. M.Sc.