Spatial and temporal variability in white spruce (Picea glauca) cone production: Individual and population responses of North American red squirrels (Tamiasciurus hudsonicus)

Habitat quality is largely heterogeneous over space and time, although common simplifying assumptions in ecological research include homogeneity of areas occupied by a population and equal resource availability among individuals. These assumptions are made due to difficulties in quantifying the food available to individuals and following the effects of food on individual performance under natural conditions. My objectives were to document temporal and spatial variability in food availability, and its effects on seed predator individual performance and population dynamics in a white spruce--red squirrel system near Kluane Lake, Yukon. This system was ideal for my study because white spruce is the only conifer present, their seeds are the primary food for red squirrels, red squirrel populations can be completely enumerated, and individuals maintain non-overlapping territories. Models including spring population density and fall cone abundance best-fit red squirrel population growth rates compared to models including a 1-year lag in food abundance, or each term alone. Cone abundance influenced the population growth rate of red squirrels more than red squirrel density. Within years, cone availability varied spatially. Synchrony in cone production patterns of individuals showed spatial variation, although most trees produced large seed crops during a mast year. Fall red squirrel territory size was influenced by the age-class of the owner (adult or juvenile), the number of offspring weaned during the year, and population density. The number of cones in a red squirrel territory was influenced by the owner's age-class and cone availability near the primary midden. Overwinter survival was most affected by territory size, rather than cone availability, suggesting alternative food may be important when cones are low. However, female reproductive success was related to cone availability in her territory. In low seed years, the highly skewed, unequal availability of food across territories suggests that spatial variation in food production, and consequently individual performance is important to short-term population persistence. Although assumptions of identical individuals have been long used in ecological research; here I have shown significant local variation in resource availability, and have provided insight into how important it may be in affecting individuals and populations in the wild.