Dispersal among populations is expected to increase population persistence through the 'rescue effect' whereby immigrants reduce local extinction rates (Brown & Kodric-Brown 1977). Immigrants may reduce extinction rates directly by reproducing in the populations to which they disperse, and indirectly by boosting genetic diversity, which can reduce negative inbreeding effects on reproductive and survival rates (Tallmon et al. 2004). Because rescue effects may be important for the persistence of populations naturally connected by dispersal, the isolation of populations with high dispersal rates through habitat fragmentation is expected to increase extinction rates. On the other hand, if dispersal rates are low and populations are naturally isolated, then fragmentation is unlikely to isolate populations further and fragmentation will not increase extinction rates.
Despite recognition of the importance of dispersal in population dynamics, few studies have attempted to quantify dispersal in amphibians (Trenham et al. 2001; Lowe 2003). Amphibians are thought to have low dispersal rates (Blaustein et al. 1994), although this may not apply to all species (Alford & Richards 1999; Marsh & Trenham 2001). Advances in capture-recapture analysis and highly variable molecular genetic markers greatly improve the potential to understand dispersal patterns. In particular, multistate capture-recapture analysis allows statistically rigorous estimation of current movement rates among populations (Nichols & Kendall 1995). Moreover, microsatellite loci are sufficiently variable to uncover patterns of gene flow over small geographical scales in order to infer historic dispersal. In this study, we used capture-recapture analysis in combination with microsatellite analysis to investigate dispersal in the Columbia spotted frog (Rana luteiventris), a pond frog distributed throughout the northwestern United States, western Canada and southeastern Alaska.