What is missing in amphibian decline research: Insights from ecological sensitivity analysis

Inventory, monitoring, and experimental studies have been the primary approaches for documenting and understanding the problem of amphibian declines. However, little attention has been given to placing human-caused perturbations affecting one or more life-history stages in the context of the overall population dynamics of particular species. We used two types of ecological sensitivity analysis to determine which vital rates have the strongest influence on the population dynamics of western toads (Bufo boreas), red-legged frogs (Rana aurora), and common frogs (Rana temporaria), pond-breeding amphibians that have declined in all or portions of their ranges. Our results suggest that post-metamorphic vital rates and highly variable vital rates both have a strong influence on the population dynamics of these species and therefore deserve more research and management attention. Ecological sensitivity analysis should be more widely applied to the issue of amphibian declines in order to identify the most plausible mechanisms of decline and prioritize which life-history stages should be the focus of research and management efforts. Future experimental studies of perturbations in one or more life-history stage should attempt to link the magnitude of the perturbation measured with the overall population-level consequences. Finally, current research, inventory, and monitoring efforts should be supplemented with demographic studies so that quantitative analyses can be applied to a wider range of species and life-history groups.