Effects of habitat complexity, prey type, and abundance on intraguild predation between larval odonates

Intraguild predation is an important interaction in which predators feed on a shared prey as well as on each other. It occurs frequently between larval odonates in freshwater lentic communities, and understanding the factors influencing this interaction remains an important objective. An experiment carried out in mesocosms and utilizing a factorial design investigated the strength of intraguild interactions between the dragonfly, Sympetrum vicinum, and the damselfly, Enallagma civile, under two levels each of habitat complexity (high or low), prey abundance (high or low) and prey type (amphipods or blackworms). Effects of treatments on size, mortality and emergence of larval odonates were evaluated. Shared prey abundance had little impact on intraguild interactions, affecting only the mass of the intraguild prey E. civile. Habitat complexity affected the size of E. civile damselflies, as length and wet mass were significantly greater in low complexity mesocosms. Prey type seemed to be the most important factor in the experiment, influencing all response variables measured. When shared prey consisted of larger, more active blackworms, intraguild predation decreased, and E. civile damselflies experienced lower mortality, achieved greater length and mass, and had greater emergence success. Results of this study suggest that prey type and habitat complexity can be more important than prey abundance in mediating intraguild predation.