Variation in behaviour of native prey mediates the impact of an invasive species on plankton communities.

Trait variation in predator populations can influence the outcome of predator-prey dynamics, with consequences for trophic dynamics and ecosystem functioning. However, the influence of prey trait variation on the impacts of predators is not well understood, especially for introduced predators where variation in prey can shape invasion outcomes. In this study, we investigated if intra-specific differences in vertical position of Daphnia influenced the impacts of the invasive zooplankton predator, Bythotrephes cederströmii, on plankton communities. Our results show that vertical position of Daphnia influenced Bythotrephes predation on smaller cladoceran species and impacts on primary production. Larger reductions in small cladoceran density and greater algal biomass were observed in mesocosms with less spatial overlap between Daphnia and Bythotrephes. These results suggest that differences in vertical position of Daphnia can alter the type and magnitude of Bythotrephes impacts in invaded systems.