Variable Breeding Strategies in a Fluctuating Environment: A Feeding Experiment in Eastern Chipmunks

Small mammals inhabiting pulsed-resource environments, such as forests with intermittent seed masting of trees, often adjust their allocation to reproduction with the drastic fluctuations in food availability. They could, for instance, plastically allocate capital resources to reproduction when food availability is low or adopt an income breeding strategy when food availability is high. We investigated how eastern chipmunks (<i>Tamias striatus</i>), a food-hoarding rodent strongly relying on the masting of beech trees (<i>Fagus grandifolia</i>), anticipate and respond to food pulses to reproduce. We supplemented a study site with sunflower seeds to buffer food availability for 2 years that were characterized by a non-mast and a beech mast. We monitored chipmunks exploitation of the feeders, body mass, and reproductive activity. We tested if food-supplemented females would reproduce in the absence of a beech mast. We compared those results with two control sites and 10 years of data on chipmunk reproduction. The probability of summer estrus significantly increased with the exploitation of feeders compared to the controls. Exploiting the feeders had a stronger effect than body mass on the probability of estrus. Still, beech masting had a broader effect on the probability of estrus across all sites than exploiting the feeders. Although most supplemented females showed oestrus during the non-mast year, as opposed to non-supplemented females, they did not fully reproduce despite their favorable body condition and the extensive hoard they accumulated. Those results suggest that summer reproduction in eastern chipmunks is not only financed by current food availability, revealing the complexity of plastic resource allocation in fluctuating environments.