Predators override rainfall effects on tropical food webs

Using an experiment with an invertebrate food web module from tank bromeliads, we manipulated the presence of an odonate predator under scenarios of 10-fold decreased, ambient, and 3-fold increased precipitation and measured responses of prey and their basal resource. Predators reduced prey abundance while precipitation did not. Both precipitation and predators, either singly or interactively, affected the elemental composition of prey.

Predators increased C:N ratios of detritivorous beetles under high precipitation, but reduced the C:N ratio of the basal resource. Precipitation reduced the N content of filter feeding mosquitoes. The observed changes in chemical composition may reflect physiological or developmental responses to stress imposed by both predators and drought.

This study demonstrates that the impact of predators and precipitation can vary substantially across a food web, including additive and synergistic effects, and numerical and phenotypic responses.