Polar bear (Ursus maritimus) foraging, spatial, and energetics ecology in the changing Arctic

• Author / Creator

  Johnson, Amy

• Climate warming in the Arctic has resulted in rapid and extensive changes to sea ice dynamics and profound ecological impacts, including changes to the timing of life history events, community structure, and food web dynamics. Sea ice-dependent species such as polar bears (Ursus maritimus) are particularly vulnerable to Arctic warming and can be useful for monitoring changing ecosystem dynamics. In this dissertation, I examine multiple aspects of polar bear ecology at different spatiotemporal scales in two declining populations to assess the underlying factors affecting population dynamics.

  To examine foraging ecology, I analyzed stable isotopes in Western Hudson Bay (WH) polar bear hair samples (1993-1994, 2004-2016) to assess intra-population variation, temporal dynamics, and relationships to sea ice dynamics. Here, I showed that adult males had the broadest diets while adult females and subadults had smaller isotopic niches, potentially increasing their sensitivity to reduced prey availability. Population isotopic values varied over time in relation to the length of the open-water period, reflecting a dietary niche shift and/or changes to ecosystem baseline isotopic values in response to climate warming.

  Secondly, I examined patterns in the spatial ecology of Southern Beaufort Sea (SB) polar bears from 2007-2011. I found broad similarities in population habitat preferences for intermediate to high sea ice concentration and seasonal movements in response to sea ice phenology. I also documented variation within the population, such that adult females with cubs-of-the-year used lower quality habitat, likely to protect dependent young. Subadult males also used lower quality habitat, which may be a mechanism to reduce intra-specific competition and/or kleptoparasitism. Monitoring habitat use can identify vulnerable demographic groups and shifts in population distribution as polar bears experience declines in optimal sea ice habitat.

  Thirdly, I analyzed the movements of an individual bear that displayed exceptionally long-distance travel from the SB population to the Chukchi Sea population (2009-2011). I compared two methods for calculating home range size and provided evidence that the Brownian bridge movement model is less biased than minimum convex polygons. Such long-distance movements and long-distance swimming events may become more common as sea ice habitat declines. As polar bear populations are relatively discrete, these movements may have implications for gene flow and population boundaries in the changing Arctic.

  Lastly, I used a novel technique to estimate WH population energy density and storage energy from abundance, age/sex structure, and body condition measurements (1985-2018). Here, I showed that energy metrics for most demographic classes declined over time in relation to earlier sea ice breakup, most significantly for solitary adult females and yearlings, demonstrating their vulnerability to nutritional stress. Additionally, population energy values declined over time in relation to earlier sea ice breakup and longer lagged open-water periods, suggesting multi-year effects of sea ice decline on WH polar bear physiological condition. Overall, this thesis provides insights into the ecological mechanisms influencing polar bear population responses to climate warming, and highlights the utility of multiple monitoring techniques for understanding changing ecological dynamics.

• Subjects / Keywords

  • Foraging ecology
  • Climate change
  • Habitat selection
  • Polar bear
  • Stable isotopes
  • Resource selection functions
  • Arctic marine ecology
  • Home range
  • Energetics
  • Ursus maritimus

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-ksp0-7957

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.