Impacts of phenological variability in a predatory larval salamander on pond food webs

Abstract

AbstractPhenological shifts are expected to affect species interactions, in part by influencing which size classes, life stages or species occur simultaneously in a community. Yet, changes in phenology beyond shifts to the first, mean or median date of an ontogenetic event are underexplored in their importance to community dynamics. Using outdoor mesocosms, we experimentally mimicked increasing variability in breeding phenology of a top predatory salamander in pond food webs (Ambystoma annulatum) to assess its impacts on its own demographic traits and survival. We also tested whether variability in predator breeding would cascade to impact survival and diversity of lower trophic levels (intermediate salamander predators, anuran tadpoles, zooplankton and periphyton). We found that only variability in body size at metamorphosis of A. annulatum was impacted by phenological manipulations, with size variability being greater at higher levels of phenological variability. Because size at metamorphosis is often correlated with adult fitness, covarying variability in body size and phenology may lead to altered population dynamics. We also found that the density and size of A. annulatum were better predictors of overall survival and diversity of amphibian prey compared to phenological variability. We speculate that overwintering mortality of A. annulatum due to pond freezing modulated the impacts of phenological variability, such that changes in demographic traits and cascading effects throughout the food web were mollified.