Variation in resource acquisition in a food-caching mammal, the North American red squirrel (Tamiasciurus hudsonicus)
Date
2023-09-25
Authors
Journal Title
Journal ISSN
Volume Title
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ORCID
0000-0001-7954-0613
Type
Thesis
Degree Level
Doctoral
Abstract
Life history theory predicts that organisms will allocate their limited energy budgets towards growth, survival, and reproduction in such a way to maximize their fitness. As organisms use energy to fuel biological processes, they must also replenish their energy levels. Given the benefits of increased energetic resources such as enhanced survival and reproductive success, why there remains a high degree of variation observed in resource acquisition remains an important question in ecology and evolution. North American red squirrels (Tamiasciurus hudsonicus) in the southwest Yukon harvest and cache white spruce (Picea glauca) cones in conspicuous larders within exclusively defended individual territories, allowing individual resource acquisition to be quantified and linked to a single individual. The seasonal nature of cone availability, compounded with high interannual variability in cone crop size makes for a fluctuating resource environment for squirrels to manage through foraging and caching efforts. Previous work shows sex-specific selection acting on total cached resources accumulated in autumn, but it was unknown as to what caused variation in cache size. Using field, laboratory, and analytical tools, I investigated hypothesized behavioural, physiological, ecological, and evolutionary drivers of observed variation in resource acquisition. Despite evidence of selection acting on caching effort, I found little evidence that phenotypic variation is attributable to heritable genetic differences, leaving a large environmental component of caching success to explore. Contributing to this remaining variation were age, sex, local resource availability in the environment, days since the birth of the most recent litter (for females, specifically in years of high resource abundance), and how much food an individual has stored off-body prior to the caching season. Interestingly, neither body fat nor body mass were associated with variation in caching success, but correlations from long-term historic data revealed males with greater body mass gain between summer and autumn cached more cones. The research I present in this thesis demonstrates the roles that sex, age, environment, and interactions thereof can play in the acquisition (or not) of a key component of the life history equation: energy.
Description
Keywords
Tamiasciurus hudsonicus, North American red squirrel, ecology, evolution, energetics, life history, behaviour, reproduction, Picea glauca, white spruce, Yukon, boreal
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Biology
Program
Biology