Fidelity and dispersal in the pond-breeding amphibian, Ambystoma opacum: Implications for spatio-temporal population dynamics and conservation

The spatio-temporal dynamics of amphibian populations and the models that describe them are largely influenced by the frequency of dispersal among breeding sites; however, dispersal has rarely been addressed rigorously in empirical studies. In a 7-year landscape-level investigation, we monitored breeding populations of marbled salamanders (Ambystoma opacum) among 14 seasonal ponds in western Massachusetts, USA, to quantify dispersal probabilities and distances. Emerging juveniles (n = 11,168) received cohort marks and adults (n = 5560 capture events) were photographed for individual identification using computer-aided dorsal pattern analysis. We found that 91.0% of first-time breeders returned to natal ponds to breed and 96.4% of experienced breeders maintained breeding site fidelity through multiple seasons. These findings confirm a high level of philopatry in this species and the prominence of local factors in determining local population trends. However, the remaining survivors dispersed to other ponds, with several individuals exceeding distances of 1000 m. Though breeding populations were clearly subdivided, dispersal at these rates may offset effects of genetic drift and inbreeding depression by increasing effective population size (through the aggregation of breeding populations). Outward dispersal probabilities were higher at ponds with small breeding populations and inward dispersal was biased toward larger populations, suggesting that salamanders were cueing to the presence of other individuals and/or to unmeasured habitat characteristics. Our findings suggest that small and dynamic local populations may operate inter dependently in a metapopulation context. Effective conservation strategies targeting these and similarly structured amphibian populations must address landscape-level processes (e.g., dispersal) as well as local demographic factors.