COS 68-6 - Impacts of increasing phenological variability on salamander demography and pond community dynamics

Wednesday, August 14, 2019: 3:20 PM
L010/014, Kentucky International Convention Center
Thomas L. Anderson1, Brittany H. Ousterhout2, Kenzi M. Stemp1, Jacob Burkhart1, David Burton1 and Jon M. Davenport1, (1)Biology, Appalachian State University, Boone, NC, (2)National Great Rivers Research and Education Center, East Alton, IL
Background/Question/Methods

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, how changes in phenology beyond shifts to the first, mean or median date of an ontogenetic event are underexplored in their importance to population and community dynamics. We experimentally mimicked increasing variability in breeding phenology of two different species of predatory salamanders (Ambystoma annulatum and Ambystoma opacum) in pond food webs to assess each species impact on its own demographic traits and survival. We also tested whether variability in predatory salamander breeding would cascade to impact survival and diversity of lower trophic levels (intermediate salamander predators, anuran tadpoles, zooplankton and periphyton). We used outdoor mesocosms that simulated pond communities, set up across two years for each of our predator species (2017-2018 = A. annulatum; 2018-2019 = A. opacum). We monitored survival, size at metamorphosis, and timing of metamorphosis of each predator and all amphibian prey. We also estimated biomass of zooplankton and periphyton, and Shannon diversity of amphibian prey.

Results/Conclusions

We found that differences in winter severity between years mediated the outcomes of our two experiments, with A. annulatum being subject to more extreme winter conditions. For A. annulatum, we found that only variability in body size at metamorphosis 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, co-varying 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. For A. opacum, which experienced less severe winter conditions, larval body size variability was affected by our phenology manipulation, with size structure significantly increasing with greater breeding variability. We anticipate such effects will translate to greater rates of cannibalism, reducing predation pressure on amphibian and zooplankton prey and a trophic cascade at lower trophic levels.