Spatially autocorrelated demography and interpond dispersal in the salamander Ambystoma californiense

The regional dynamics of pond-breeding amphibians are often discussed in the context of metapopulations, under the assumption that individual ponds support distinct subpopulations. We used a combination of indirect and direct methods to assess the spatial population structure of California tiger salamanders (Ambystoma californiense) relative to two basic requirements of metapopulation models: (1) that patches support somewhat independent populations linked by dispersal, and (2) that interpatch dispersal probabilities decline as distance increases. Over three consecutive field seasons we captured, marked, and released adult California tiger salamanders at 10 breeding ponds. We observed interpond dispersal by these experienced breeders, and also by first-time breeders marked as newly metamorphosed juveniles at one pond. Spatial autocorrelation of pond-specific demographic parameters suggests that these ponds meet both of these requirements of metapopulation theory. Direct observations of interpond movement by marked individuals support the conclusions of the autocorrelation analyses but reveal relatively high probabilities of interpond movement by both first-time and experienced breeders. We conclude that the subpopulations utilizing these ponds are too closely linked by dispersal for classical extinction-colonization metapopulation dynamics to apply. High probabilities of dispersal are predicted to constantly supply less isolated ponds in this system with dispersers such that local extinctions will be rare. Based on population genetic theory, the high probability of interpond movement is also predicted to prevent significant genetic divergence among ponds over large areas.