Effective to census population size ratios in two Near Threatened Mediterranean amphibians: Pleurodeles waltl and Pelobates cultripes

Abstract

Efforts to mitigate amphibian declines are hindered by a lack of information about basic aspects of their biology and demography. The effective to census population size ratio (Ne/Nc) is one of the most important parameters for the management of wildlife populations because it combines information on population abundance and genetic diversity and helps predict population viability in the long term. Few studies have calculated this ratio in amphibians, which sometimes show low ratios, associated with a higher extinction risk. Here we integrate field-based (capture-mark-recapture studies, egg string counts) and molecular approaches (estimation of the effective number of breeders (Nb) and the effective population size (Ne) based on genotypes from larval cohorts and candidate parents) to produce the first estimates of the Ne/Nc and Nb/Nc ratios in two amphibians, the Iberian ribbed newt Pleurodeles waltl and the western spadefoot Pelobates cultripes. Additionally, we investigate sex-biased dispersal in both species based on direct (field observations) and indirect (genetic) evidence. Both species showed similar ratios, slightly lower in Pleurodeles (0.21–0.24) than in Pelobates (0.25–0.30). Observed displacement rates were low in both species (P. waltl = 0.51%; P. cultripes = 1.23%). We found no evidence for sex-biased dispersal in P. cultripes, but both direct and indirect evidences suggest a tendency for female-biased dispersal in P. waltl. We discuss differences in the genetic estimates of Ne and Nb provided by three inference methods and the implications of our findings for the management of these species, characteristic of Mediterranean wetlands in the Iberian Peninsula and listed as Near Threatened.