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The role of food limitation in the snowshoe hare (Lepus americanus) population cycle

  • Author / Creator
    Majchrzak, Yasmine N
  • Understanding the causes behind population cycles is a fundamental issue in ecology, and has been the focus of research for decades. One of the most prominent examples of cyclical species is the snowshoe hare (Lepus americanus), a primary prey species in the North American boreal forest that exhibits fluctuations in abundance over 8-10 year periods. The potential for food limitation to cause changes in hare abundance has been examined, through manipulative experiments where individuals are provided supplemental food. However, in previous studies food addition was administered on a large scale, which can be problematic due to increased immigration to the area by other hares causing a predator-pantry effect. Individual-based food addition is therefore an optimal method for investigating the role of food in the snowshoe hare cycle. My primary objective was to evaluate the effect of food limitation on snowshoe hare demography, and determine the potential mechanisms of how food acts by examining behaviour, body condition, and physiology. To accomplish this, I radio-collared hares in the Kluane Lake area of the Yukon, Canada during the increase, peak, and decline phases of the cycle and fed a subset of individuals throughout the winter from selective feeders. These feeders allow controlled access to only the specific pit-tagged individuals. Over the study, I found that food supplementation significantly improved survival, with the largest effect size occurring during the population increase phase. Fed individuals also gave birth to larger offspring and produced larger litters. The demographic effects between treatments were likely driven by differences in behaviour or body condition. Fed individuals foraged less per day and spent a larger proportion of the foraging time vigilant, while maintaining a larger body mass. They further had reduced movement rates, and selected for conifer habitat relative to controls. Surprisingly, food supplementation increased hare stress responses to a hormone challenge, but simultaneously increased their ability to buffer against this heightened response, through increased corticosteroid binding capacity. Food supplemented individuals had improved body condition, in terms of blood indices and lower over-winter mass loss. I also found that changes in the indicators of stress in snowshoe hares during this study did not echo those observed in previous cycles. In combination, this thesis provides evidence that food limitation contributes to the demographic changes observed across the cycle, particularly in the increase phase, which may be caused by changes in behaviour and body condition.

  • Subjects / Keywords
  • Graduation date
    Fall 2020
  • Type of Item
    Thesis
  • Degree
    Doctor of Philosophy
  • DOI
    https://doi.org/10.7939/r3-7v8d-3e75
  • 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.