Contrasting demographic trends and asymmetric migration rates in a spatially structured amphibian population.

Abstract

Natural populations often persist at the landscape scale as metapopulations, with breeding units (subpopulations) experiencing temporal extinction and recolonization events. Important parameters to forecast population viability in these systems include the ratio of the effective number of breeders (Nb ) to the total number of adults (Na ) and migration rates among subpopulations. Here, we present the results of a 10-year integrative monitoring program of a metapopulation of the Iberian green frog (Pelophylax perezi) in central Spain. We characterized population dynamics at two main breeding ponds (Gravera and Laguna) using capture-mark-recapture data to estimate Na in each breeding season, and multilocus genotypes to estimate the effective population size (Ne ), Nb , individual breeding success, and migration rates. Both ponds experienced population decline after a dry season, with Gravera subsequently recovering and Laguna suffering a bottleneck associated with genetic impoverishment. In this subpopulation, average allelic richness and private alleles decreased from 2010 (10.87 and 1.67, respectively) to 2018 (8.0 and 0.20). The Nb /Na ratio in Laguna in 2018 was twice as high (0.95) than in Gravera (0.41) or in pre-bottleneck Laguna (0.50), suggesting plasticity or genetic compensation through increased individual breeding success. Migration rates were asymmetric between ponds, with a stronger contribution from Gravera to Laguna (29.9% vs. 16.2% in the opposite direction) that may result in a rescue effect. This study emphasizes the importance of integrative demographic approaches for the monitoring of natural populations based on a better understanding of their spatio-temporal dynamics, which provides valuable information for conservation actions.