Terrestrial movement, dispersal and adult survival of marbled salamanders (<i>Ambystoma opacum</i>): Implications for metapopulation dynamics and conservation
Habitat loss and fragmentation are among the most serious threats facing amphibian populations globally. Given the prevalence of these threats, it is essential that conservation planners understand the spatial scales at which amphibian populations operate and minimize local and regional extinction risks. We conducted a landscape-level investigation of population processes in marbled salamanders (Ambystoma opacum) distributed among 14 seasonal ponds in western Massachusetts. Using capture-recapture methods, we monitored breeding populations from 1998 to 2005 to evaluate terrestrial movement distances (Chapter 1), develop methodology for identifying individuals (Chapter 2), quantify dispersal probabilities and distances (Chapter 3), and evaluate survival and breeding probabilities in adults and the degree to which they are correlated among breeding populations (Chapter 4).
In six field seasons, we recorded over 6,000 captures of adult marbled salamanders and 8,000 captures of newly emerging juveniles. Six of the 14 ponds supported relatively persistent breeding populations. Nearly 100% of adults and over 70% of juveniles moved to terrestrial habitats farther than 30 m from breeding ponds, and some juveniles moved greater than 1,200 m in their year of emergence. Both first-time and experienced breeders showed high fidelity to natal ponds; however, 9% and 3.6% of these individuals, respectively, dispersed to non-natal breeding sites. Adult survival probabilities did not vary substantially between sexes or among most breeding populations. Simulations estimated that approximately 50% of individuals that survive to breed once do not live to breed again, but approximately 25% will survive to breed 3 or more times.
Collectively, our results demonstrate that breeding populations of marbled salamanders are prone to significant variability over time, with much of this variability concentrated in the egg and larval life stages. Given relatively limited life spans and frequent reproductive failures, many breeding populations may be vulnerable to local extinctions over the course of several decades; however, occasional dispersal among populations may offset both genetic and demographic factors contributing to local extinction risks. Marbled salamanders in Massachusetts may be best described by a dynamic “source-sink” metapopulation model, suggesting that conservation strategies must extend beyond breeding wetlands to maintain adult survival and metapopulation processes.