The five data chapters in my dissertation were conceived and prepared as separate research projects, each intended for independent publication and united by the common theme of investigating the interactions between conifer seeds and the nutritional and population ecology of small mammals. As such, there is some degree of repetition in parts of the introduction and methods sections. These have been kept to a minimum, but have been retained in order to allow each chapter to stand as an independent manuscript. Chapters 2 and 3 have been published, Chapter 4 is currently under review for
publication, and a combined version of Chapters 5 and 6 is in press.
In Chapter 2, I investigated the preferences of five species of small mammals (the deer mouse, red-backed vole, heather vole (Phenacomys intermedius), long-tailed vole (Microtus longicaudus), and meadow vole (Microtus pennsylvanicus) for white spruce, subalpine fir, and lodgepole pine seeds. Previous research has examined the diets of these rodents to varying degrees, but little is known about their granivorous food habits in relation to conifer seeds. Given that these conifers are common associates in western Canada, and that small mammals are major post-dispersal seed predators, determining their seed preferences has important implications for understanding how they partition resources in nature, as well as how differential seed predation may influence plant
regeneration and community dynamics. This study was conducted using cafeteria-style feeding experiments, both in the laboratory and in the field.
In Chapter 3, I examined the efficacy of white spruce, subalpine fir, and lodgepole pine seeds as major food resources to deer mice and red-backed voles. While it has been shown that conifer seeds are a component of the diet of many rodents, it is not known whether these seeds can be used as a major food source, depending on their nutritional value and PSC contents. Investigating this is critical to understanding whether, and how, different rodents can utilize large quantities of specific conifer seeds; this is one of the key mechanisms underlying their population interactions with seed production by
coniferous trees. I examined the nutritional quality of these seeds, as well as the effects of restricted seed-diets on the survival, body condition, food consumption patterns, and gut morphology of rodents in the laboratory.
In Chapter 4, I investigated the effects of conifer seed quality and abundance on the foraging behaviour of deer mice and red-backed voles. The decision to consume or cache seeds when they are encountered can be influenced by numerous factors such as their abundance, nutritional value, and PSC contents. While low quality conifer seeds are avoided by rodents in the laboratory when other food options are available, they may be preferentially cached in the field when abundant for future use during unpredictable times. I used artificial food patches in the field to experimentally examine the foraging behaviours of rodents in response to varying abundances of white spruce and subalpine fir seeds. I also used a standardized variant of giving-up densities to assess rodents’ perception of the quality of seeds in patches, as well as the lower threshold density at which they cease active foraging for each seed species. Further, these measures allowed
me to examine two key assumptions underlying the hypothesis that rodent populations respond to fall mast seeding by conifer trees: (1) the seeds are cached for use in the fall and winter; and (2) a sufficient quantity of seeds are released during a masting event to effectively enhance the food supply to the population.
In Chapter 5, I investigated the effects of variable conifer seed production on deer mouse populations. While the relationship between rodent populations and mast seeding is clear and well-documented in deciduous forests, there is little evidence in the literature of consistent effects of fall conifer masting on rodent populations. Based on my knowledge of interactions between conifer seeds and individual mice from Chapter 2-4, I
hypothesized that there would be a positive relationship between mouse populations and white spruce seed production, but no effect of subalpine fir masting. I tested this
hypothesis by examining the population, breeding, and body mass dynamics of a deer mouse population in relation to white spruce and subalpine fir seed production over a 10- year period.
Finally, in Chapter 6, I investigated the effects of natural food supplementation on deer mouse demography. Based on my knowledge of interactions between conifer seeds and deer mice, both at an individual- and population-level, from Chapters 2-5, I supplemented a long-term deer mouse population monitoring grid with an excess of white spruce seeds in order to test the hypothesis that increased seed availability to mice during the fall would lead to enhanced survival and breeding. This population was compared to a control population from a nearby long-term monitoring grid for several years prior to, and one year after, supplementation in order to determine the effect of increased fall spruce seed availability on the population, breeding, and body mass dynamics of deer mice.