Multiple predator effects among larval stages of pond-breeding salamanders

Thomas L. Anderson, Biology, Southern Illinois University Edwardsville, Edwardsville, IL and Jon M. Davenport, Biology, Appalachian State University, Boone, NC

Background/Question/Methods
When multiple predators co-occur in a community, they can have either additive or non-additive impacts on prey survival. Non-additive impacts, or emergent multiple predator effects (MPEs), occur when foraging rates of combined predators cannot be predicted based on their individual foraging rates, resulting in either prey risk enhancement or reduction. We conducted several experiments to assess whether emergent MPEs occur between different species of larval salamanders, as well as how different factors (prey density and the occurrence of an additional top predator) may mediate emergent MPEs. Additionally, we experimentally tested how emergent MPEs affect the diversity of anuran prey assemblages. The prey density experiment examined emergent MPEs between larval ringed and marbled salamanders consuming Southern leopard frog tadpoles. The top predator experiment examined MPEs between larval spotted and small-mouth salamanders consuming hylid tadpoles, either in the presence or absence of visual/chemical stimuli from an aeshnid dragonfly larva. The test of MPEs on prey diversity again used larval ringed and marbled salamanders, using larvae of five amphibians as prey. We monitored survival of prey items, and assessed whether emergent MPEs occurred by comparing the observed survival against expected survival using the multiplicative risk model.
Results/Conclusions
Across all three experiments, we found that larval salamander had additive impacts on prey, rather than exhibit emergent MPEs. This occurred despite the different contexts under which we investigated MPEs, including prey density, the occurrence of an additional top predator, and when multiple prey occurred together. Furthermore, we found larval salamanders had additive impacts on prey diversity. Altogether these results suggest that emergent MPEs may not play a critical role in structuring predator-prey dynamics in this system, despite substantial a priori knowledge on larval aggression that would have suggested strong interference among predators.