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

Abstract

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 (Formula presented.) and the effective number of breeders (Formula presented.) of two breeding populations to (1) document changes in the number of breeding adults over the 9-year study duration, (2) determine whether (Formula presented.) and (Formula presented.) provide similar information about population size and trends and (3) compare alternative demographic and genetic approaches for estimating (Formula presented.). We found that genetic estimates of (Formula presented.), particularly if averaged across multiple estimation methods, closely tracked spatiotemporal variation in (Formula presented.). Demographic estimates of (Formula presented.) also closely tracked (Formula presented.) 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 (Formula presented.) to reliably inform management decisions. In these populations, (Formula presented.) 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 (Formula presented.) estimation methods in guiding recovery efforts of threatened and endangered species.