Chipmunk body mass variations and life-histories in a pulsed resource ecosystem

Phenotypic plasticity is the most immediate mechanism of adaptative
response to environmental change. Studying plastic changes in response to
fluctuating environments provides insights into how such adjustments may
impact life-history traits. Here, we used a 14-year dataset of repeated
body mass measurements in male eastern chipmunks (Tamias striatus) to
assess the extent of plastic changes for this trait in a resource pulse
ecosystem. We first determined the magnitude of variation in body mass at
the population level in response to the drastic change in food resource
availability from American beech tree seeds (Fagus grandifolia). Males
that emerged in the spring from winter torpor following a non-mast year
had a lower body mass than males emerging after a mast year, but they
tended to recover this loss by mid-June. We found significant
among-individual variation in spring body mass plasticity (i.e.,
individual by environment interaction, I x E). We then investigated the
relationships between individual spring body mass plasticity, longevity
and lifetime reproductive success. Interestingly, heavier males lived
longer than lighter males, but more plastic males had a lower longevity
and lower lifetime reproductive success than less plastic males. The
report of such plastic response in a stochastic resource system provides
valuable insights into the interplay between the costs and benefits of
phenotypic plasticity as an adaptation to environmental fluctuations.