Demographic sensitivity and persistence of the threatened white- and orange-bellied frogs of Western Australia

Anurans have been the subject of numerous experimental and monitoring studies, yet their autecology under natural conditions remains poorly understood. Previous work has focussed on the pre-metamorphic life stages, with data suitable for estimating demographic parameters for all life stages collected in few species. This deficiency has almost certainly confounded current views of amphibian autecology and understanding of which mechanisms of decline represent the greatest threats to the persistence of amphibian species. We used a stage-structured metapopulation model, parameterised with comprehensive field data, to explore the sensitivity of two species of myobatrachid frogs from the southwest of Australia, Geocrinia alba and G. vitellina, to changes in demographic parameters at all life stages. The simulation modelling indicated that the population dynamics of both species were consistently most sensitive to changes in juvenile survival, then to fecundity, and third to both adult survival and standard deviation of survival to about equal extent. In practical terms, this indicates that management interventions which attempt to mitigate reductions in juvenile survival are likely to be most successful in arresting anuran metapopulation declines.