Recent research investigating causes of global amphibian decline has shifted from focusing on a single factor and life-stage to examining multiple potential threats and their effects on populations at multiple life stages. Such demographic studies provide an opportunity to test for trends that associate habitat alterations with amphibian population dynamics. Habitat alterations can occur in either the terrestrial (eg., deforestation) or the aquatic (eg., agricultural run-off) habitat and will affect the amphibian vital rates therein. The population-level effect of these alterations, however, depends on the sensitivity of the population growth rate (λ) to changes in the vital rates in each habitat. We ask whether the sensitivity of different vital rates depends on the life history (longevity) of the population. If generalities exist, then the relative importance of threats attributed to amphibian decline can be predicted, partially, by knowledge of the organism’s life history. We compiled all amphibian population matrices from the literature to look for relationships between amphibian longevity and the elasticity of λ to perturbations in vital rates. For each species, we calculated two longevities: one estimated from the literature and one based on the matrix. We summed elasticity values for vital rates corresponding to either habitat type.
Results/Conclusions
We found that as the longevity (regardless of how calculated) of amphibians increased, population growth rate became less sensitive to changes in vital rates associated with the aquatic habitat (e.g., tadpole survivorship) and more sensitive to changes in vital rates associated with the terrestrial habitat (e.g., adult survivorship). We explored how realistic changes in vital rates caused by habitat alterations (based on published experiments and observations) affect λ of one typical long-lived and one short-lived amphibian population. In a typical short-lived amphibian, we show that realistic effects of habitat alterations on vital rates have large effects on λ when those alterations occur in the aquatic but not terrestrial habitat, and that the opposite is true for a typical long-lived amphibian. Our study indicates that knowledge of amphibian longevity can predict which habitat alterations will have the greatest affect on λ, and thus might be important agents of amphibian population decline.
