Do changes in berry crops drive population fluctuations in small rodents in the southwestern Yukon?

Small mammals in boreal forest ecosystems fluctuate dramatically in abundance and 1 possible mechanism to explain these changes is the bottom-up hypothesis of variation in food supplies. Here we ask if variation in berry crops produced by 6 major species of dwarf shrubs and herbs, epigeous mushroom crops. and white spruce seeds allow us to predict changes in the abundance of the red-backed vole (Myodes [ = Clethrionomys] the deer mouse (Peromyseus maniculatus), and field voles (Microtus oeconomus and M pennsylvanicus combined) over 13 years (1997-2009) in the Kluane Lake region of the southwestern Yukon, Canada M rutilus is the dominant rodent in these forests. comprising 64% of the catch. Overwinter survival is a key demographic variable in all these rodents, and the winter food supply principally berries produced the previous summer may be I key to overwinter survival We predicted that berry, mushroom, and tree seed crops in year / would produce changes in rodent density in year t + I. We could explain statistically 78-98% of the variation in May and August abundance of all 3 rodent species with indices of berry crops and mushrooms in the previous summer For M rutilus the critical predictor was berry crops of Empetrum nigrum For P maniculatus, the critical species were Arctostaphylos uva-urst, A rubara, and mushrooms. Spruce seed crops were not significantly correlated with rodent densities or changes in density A large fraction of the variation in rodent numbers in this ecosystem is explained by a simple bottom-up model of population limitation. DOI 10 1644/09-MAMM-A-005.1