Non-additive predation in littoral habitats: Influences of habitat complexity

The combined effects of predators on prey in structurally complex habitats may not always be described by additive models. Changes in habitat complexity can affect the rates of consumption by individual predators as well as alter the interactive, combined effects of predators with contrasting foraging styles. We examined the combined consumption of a common prey by two predators across a gradient of three habitat complexities. In microcosm experiments, consumption of larval mayfly prey (Cloeon cognatum) by juvenile bluegill sunfish (Lepomis macrochirus) and libellulid dragonfly larvae (Erythemis simplicicollis) exceeded additivity at low habitat complexity, but were additive at higher levels of complexity. Prey capture by odonates was unaffected by fish presence during both day and night. At low stem density, fish capture more mayfly larvae than expected in the presence of dragonflies than in their absence, while consumption by dragonflies is unchanged in the presence of fish. Both the behavioral attributes of predators and prey as well as structural complexity of their habitat affect encounter rates, and thus their net interaction.