Effective population size is strongly correlated with breeding pond size in the endangered California tiger salamander, Ambystoma californiense

Maintaining genetic diversity and population viability in endangered and threatened species is a primary concern of conservation biology. Genetic diversity depends on population connectivity and effective population size (N-e), both of which are often compromised in endangered taxa. While the importance of population connectivity and gene flow has been well studied, investigating effective population sizes in natural systems has received far less attention. However, N-e plays a prominent role in the maintenance of genetic diversity, the prevention of inbreeding depression, and in determining the probability of population persistence. In this study, we examined the relationship between breeding pond characteristics and N-e in the endangered California tiger salamander, Ambystoma californiense. We sampled 203 individuals from 10 breeding ponds on a local landscape, and used 11 polymorphic microsatellite loci to quantify genetic structure, gene flow, and effective population sizes. We also measured the areas of each pond using satellite imagery and classified ponds as either hydrologically-modified perennial ponds or naturally occurring vernal pools, the latter of which constitute the natural breeding habitat for A. californiense. We found no correlation between pond area and heterozygosity or allelic diversity, but we identified a strong positive relationship between breeding pond area and N-e, particularly for vernal pools. Our results provide some of the first empirical evidence that variation in breeding habitat can be associated with differences in N-e and suggest that a more complete understanding of the environmental features that influence N-e is an important component of conservation genetics and management.