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

Abstract

Phenological 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.

Asymmetric density‐dependent competition and predation between larval salamanders

“…We began checking each tank for metamorphosing animals in early May 2019, which corresponded to the timing of metamorphosis in previous experiments (Anderson et al., 2017, 2020; Anderson & Semlitsch, 2014). We removed individuals that had reabsorbed their gills, and recorded their mass (g) and date of metamorphosis.…”

Limited population and community effects of hatching asynchrony in a pond‐breeding salamander

“…Even within a given taxonomic grouping, not all species will be equally affected by phenological shifts. For example, life history traits and survival of some amphibians are clearly affected by changes in phenology (Boone et al, 2002;Carter & Rudolf, 2019;Rasmussen & Rudolf, 2015), whereas in other amphibians this relationship is more ambiguous (Alford, 1989;Anderson et al, 2017Anderson et al, , 2020. Therefore, further investigation into when and how species interactions will be disrupted by phenological change and whether such shifts in interactions cascade across multiple trophic levels are clearly needed.…”

“…Amphibians have well‐documented changes in phenology, especially for metrics like the first or median date of breeding activity (Blaustein et al, 2001; Lunghi, 2018; Todd et al, 2011). Other measures of phenology are less well understood, though several recent experiments have begun to unravel how factors like the degree of hatching synchrony affect amphibian dynamics (Anderson et al, 2020; Carter & Rudolf, 2019; Rasmussen & Rudolf, 2015, 2016). There is also a substantial body of literature on how the timing of breeding and/or hatching impacts species interactions through intra‐ and interspecific priority effects (Boone et al, 2002; Lawler & Morin, 1993; Murillo‐Rincón et al, 2017; Rudolf, 2022; Wilbur & Alford, 1985).…”