The preferences of the deer mouse ( Peromyscus maniculatus (Wagner, 1845)), southern red-backed vole ( Myodes gapperi (Vigors, 1830)), heather vole ( Phenacomys intermedius Merriam, 1889), long-tailed vole ( Microtus longicaudus (Merriam, 1888)), and meadow vole ( Microtus pennsylvanicus (Ord, 1851)) for lodgepole pine ( Pinus contorta Dougl. ex Loud.), white spruce ( Picea glauca (Moench.) Voss), and subalpine fir ( Abies lasiocarpa (Hook.) Nutt.) seeds were investigated using cafeteria-style feeding experiments. Seed selection by P. maniculatus and M. gapperi in the field was also studied. Peromyscus maniculatus, M. gapperi, M. longicaudus, and M. pennsylvanicus showed a distinct preference for lodgepole pine seeds and avoidance of subalpine fir seeds, and consumed the different species of seeds in similar relative proportions. Phenacomys intermedius behaved very differently from the other rodent species in that it did not show a preference among seed species, and consumed very few seeds in total. Findings from the field seed selection trials were consistent with laboratory results. We suggest that postdispersal seed predation by small mammals could limit the recruitment success of lodgepole pine and white spruce, but would not be a major problem in the regeneration of subalpine fir stands. This could provide an advantage for subalpine fir over neighbouring competitive species.

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a b s t r a c tConifer seeds are a component of the diet of many rodents, but it is not known whether these seeds can be used as a major food source by rodents. Investigating this is critical to understanding how individual rodents utilize conifer seeds, and how their populations interact with seed production by coniferous trees. We examined the effects of conifer seed-diets on survival, body condition, food consumption, and gut morphology of deer mice (Peromyscus maniculatus) and southern red-backed voles (Myodes gapperi) in the laboratory. Experiments were conducted for 14 days using control food (laboratory rodent chow) and lodgepole pine (Pinus contorta), white spruce (Picea glauca), and subalpine fir (Abies lasiocarpa) seeds. The nutritional compositions of these seeds were also analyzed. Subalpine fir seeds contained the lowest crude protein content and highest fibre content relative to the other seeds. 60% of voles fed subalpine fir seeds were euthanized prior to the end of the experiment after losing greater than 25% of their initial body mass, whereas all mice survived to the end of the experiment in each group. Body masses of mice fed subalpine fir seeds were lower than those fed control food early in the experiment, but they compensated for this by increasing seed intake over the remainder of the experiment. They also retained more digesta in the caecum, which could increase digestion efficiency of the low-quality seeds. On the other hand, voles did not compensate for the low quality of subalpine fir seeds behaviourally (food intake) or morphologically (gut dimensions), and decreased in body mass dramatically. They also decreased in body mass in the longterm on white spruce seed-diets. It is likely that plant secondary metabolites played a major role in the deterioration of body condition of voles fed subalpine fir and white spruce seeds. These results indicate that conifer seeds are a sufficient food resource for mice, but cannot be used by primarily herbivorous voles as a major/sole food source.

Summary1. Pulsed resources have significant effects on population and community dynamics in terrestrial ecosystems. Mast seeding is an important resource pulse in deciduous forests; these boom and bust cycles of seed production generate strong lagged population responses by post-dispersal seed predators such as rodents, which then cascade through multiple trophic levels and regulate population dynamics of their predators and prey. However, similar interactions in another major pulsed system, coniferous forests, are inconsistent, and the effects of interannual variation in conifer seed production on many consumer populations are largely unknown. 2. We used large-scale manipulation and intensive monitoring to examine the population dynamics of deer mice (Peromyscus maniculatus) in relation to fall seed production by two northern conifers, white spruce (Picea glauca) and subalpine fir (Abies lasiocarpa). Previous studies have shown that spruce seeds are a preferred food source of mice, while fir seeds are generally avoided if other foods are available. Therefore, we expected that there would be a positive relationship between mouse demography and previous spruce seed production, but no effect of fir mast seeding. 3. Supplementation of a mouse population using spruce seeds indicated that increased fall spruce seed availability can enhance overwinter survival and population densities in the following spring, summer, and fall. However, long-term population monitoring indicated that mouse demography was not positively affected by spruce mast seeding, likely due to strong interspecific competition with the North American red squirrel (Tamiasciurus hudoniscus), a dominant pre-dispersal spruce seed predator. 4. Conversely, we observed an unexpected delayed effect of fir mast seeding, where increased fall fir seed production did not influence overwinter or spring mouse demography, but instead enhanced summer survival, body masses and pregnancy rates of overwintered adults. This led to increased summer population densities and may have been mediated by population responses of invertebrate post-dispersal seed predators to increased fir seed availability. 5. Our results indicate that rodent responses to resource pulses in coniferous forests are more complex than in deciduous environments and reveal previously unobserved direct and indirect consumer-resource dynamics that require further examination. This system is ideal for the large-scale, integrative ecosystem studies that ecologists are encouraged to pursue.

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