Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Dr. John S. Millar


Conifer seeds are a component of the diet of many rodents, and post-dispersal seed predation by rodents is often implicated as a critical constraint on the regeneration of coniferous forests. However, little is known about the effects of conifer seed availability on individual rodents and their populations. The over-arching goal of this dissertation was to investigate the effects and implications of conifer seed production on the foraging and population dynamics of northern small mammals. The predominant conifer study species were white spruce (Picea glauca) and subalpine fir (Abies lasiocarpa), and the main rodents examined were the deer mouse (Peromyscus maniculatus) and southern red-backed vole (Myodes gapperi).

Nutritional analysis and laboratory experiments showed that spruce seeds are a high quality food source to rodents. Mice were able to maintain body condition on diets restricted to these seeds, and voles were able to use spruce seeds as a sole food source in the short-term. In the field, caching rates of spruce seeds varied with seed abundance, but rodents readily consumed these seeds within experimental patches regardless of abundance.

Conversely, fir seeds were avoided by rodents in experiments, as was expected based on their low nutritional value and high concentration of plant secondary compounds. Mice increased food intake and retention of digesta in the caecum to maintain body mass on diets restricted to fir seeds. However, voles did not compensate for this low quality seed-diet, and their body condition deteriorated rapidly. In the field, rodents disregarded fir seeds as a valuable resource for current or future use, even at exaggeratedly abundant seed densities.

Given these individual-level interactions, the rodent population responses to conifer mast seeding that I observed were unexpected. Summer mouse densities and breeding varied with previous fir seed production, although this may have been mediated by population responses of invertebrate post-dispersal seed predators to fir seed availability. In contrast, mouse demography was not affected by spruce mast seeding, but likely due to interspecific competition with the North American red squirrel (Tamiasciurus hudsonicus), a dominant pre-dispersal spruce seed predator. These results reveal direct and indirect consumer-resource pulse dynamics that require further examination.