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Breeding dispersal, male mating tactics, and population dynamics of arctic ground squirrels Gillis, Elizabeth A.

Abstract

Arctic ground squirrels are the northernmost hibernating mammal and they live in an extremely harsh and unpredictable environment with a short growing season. This environment has the potential to exert strong selection pressure on life-history traits and behaviour. I studied arctic ground squirrels living at high elevation in alpine tundra in Southwest Yukon in order to answer 5 main questions: (1) How do changes in elevation and associated habitat affect demography of arctic ground squirrels? (2) What is the fate of adult males that disappear at very high rates from local populations? (3) What factors are correlated with an individual's probability of death and dispersal?, (4) What factors are correlated with a male's reproductive tactic and success?, and (5) Why do adult males disperse? Female arctic ground squirrels living at high elevation in the alpine had higher reproductive output and survival during the active season, but lower survival over winter, than their counterparts living at lower elevation in the boreal forest. A demographic model indicated that the forest was sink habitat (λ < 1) but that the alpine habitat maintained a ground squirrel population in the absence of immigration (λ ≥ 1). Adult males had two peak periods of disappearance during the active season - late in the mating season, caused by mortality, and around the time of juvenile emergence, caused by dispersal. Age was an important predictor of both mating season and winter survival, with older (≥ 2 years old) males having a lower survival rate than yearlings. Age may also have played a key role in the mating and dispersal tactics of adult males. Older males invested more energy into reproduction than yearlings, and the reasons why yearlings and older males disperse differed. Older males may have dispersed to avoid mating with their daughters, to increase their access to mates, or to increase their access to unrelated mates, but yearlings appeared to disperse for other reasons. I combined the results of my study and previous studies in a conceptual model relating mating tactics, natal and breeding dispersal, and survival in male arctic ground squirrels. This model provides testable hypotheses about casual relationships among variables.

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