PRINCES AND PAUPERS: EFFECTS OF ANNUAL AND EARLY-LIFE RESOURCE VARIABILITY ON DEMOGRAPHY IN POPULATIONS OF COMMON GARTER SNAKES, THAMNOPHIS SIRTALIS

Resource availability, acquisition, and assimilation drive trade-offs and shape life-history strategies within individuals and across populations. With limited dispersal ability and notable life-history variation, garter snakes provide unique model systems for understanding population responses to variable environments. We investigated the relationship between demographic parameters and the environment for montane populations of Common Garter Snakes (Thamnophis sirtalis) using a 16-year mark-recapture data set. We quantified patterns in survival, reproduction, and growth and how they vary between sexes, among populations, and in response to annual variability in resource conditions. We found that reproductive output increased in years when prey availability was greater. In contrast, survival varied among populations and between males and females but not with respect to annual differences in environmental conditions. We found an interaction between early-life resource conditions and sensitivity to resource availability in later life. Growth was accelerated in years of higher prey availability for individuals that experienced poor prey conditions in their first year of life. Overall, our findings reveal spatiotemporal variation in growth and reproduction that are consistent with fluctuations in local resources and are complemented by trait plasticity in populations of a sympatric garter snake. Our results provide important insights regarding demography of ectothermic vertebrates with indeterminate growth and elucidate influences of annual variation in prey abundance on survival, reproduction, and growth and effects of early-life conditions. Importantly, our results suggest that efforts to predict how populations will respond to fluctuating environments should incorporate early-life environment to account for context-dependent variation in demographic processes.