Comparing estimates of census and effective population size in an endangered amphibian

The field of conservation has seen a shift in focus from monitoring trends in census population size to trends in `effective' population size. Numerous genetic methods exist for estimating effective population size, resulting in uncertainty among conservation practitioners as to which methods are most appropriate when conducting population assessments or evaluating recovery efforts. Demographic approaches offer a promising avenue to provide a link between census and effective population size using life-history information, but rarely do studies have all three sources of data (genetic, demographic, life history) necessary to perform an explicit evaluation of their performance. Using data from a long-term study of reticulated flatwoods salamanders (Ambystoma bishopi) in western Florida, USA, we assessed the magnitude of temporal variation in census population sizes oNTHORN and the effective number of breeders Nbo THORN of two breeding populations to (1) document changes in the number of breeding adults over the 9-year study duration, (2) determine whether N and Nb provide similar information about population size and trends and (3) compare alternative demographic and genetic approaches for estimating Nb. We found that genetic estimates of bN b, particularly if averaged across multiple estimation methods, closely tracked spatiotemporal variation in N. Demographic estimates of Nb also closely tracked N but were sensitive to the assumed variance in reproductive success. In the absence of genetic information, detailed knowledge of mating systems and the environmental factors that skew reproductive contributions appear necessary for demographic Nb to reliably inform management decisions. In these populations, bN b appears too small (<40 individuals) to confer long-term genetic resilience, highlighting the importance of restoring landscape connectivity and indicating that caution must be taken when sourcing animals for reintroduction efforts. More generally, our study reveals insights into the utility of alternative Nb estimation methods in guiding recovery efforts of threatened and endangered species.

Automated summary

The focus of conservation has shifted from monitoring census population size to effective population size. There are various genetic methods available for estimating effective population size, causing uncertainty among conservation practitioners. This study used data from a long-term study of reticulated flatwoods salamanders in Florida, USA, to assess temporal variation in census population size and effective number of breeders. The study found that genetic estimates of the effective number of breeders closely corresponded to spatiotemporal variation in population size. Demographic estimates were also close, but sensitive to assumptions about reproductive success variance. The study highlights the importance of genetic resilience and landscape connectivity in conservation efforts.