Opportunistic predator prefers habitat complexity that exposes prey while reducing cannibalism and intraguild encounters.

Structural features of habitat are known to affect the density of predators and prey, and it is generally accepted that complexity provides some protection from the environment and predators but may also reduce foraging success. A next step in understanding these interactions is to decouple the impacts of both spatial and trophic ingredients of complexity to explicitly explore the trade-offs between the habitat, its effects on foraging success, and the competition that ensues as predator densities increase. We quantified the accumulation of spiders and their prey in habitat islands with different habitat complexities created in the field using natural plants, plant debris and plastic plant mimics. Spiders were observed at higher densities in the complex habitat structure composed of both live plants and thatch. However, the numerically dominant predator in the system, the wolf spider Pardosa milvina, was observed at high densities in habitat islands containing plastic mimics of plants and thatch. In a laboratory experiment, we examined the interactive effects of conspecific density and habitat on the prey capture of P. milvina. Thatch, with or without vertical plant structure, reduced prey capture, but the plastic fiber did not. Pairwise interactions among spiders reduced prey capture, but this effect was moderated by thatch. Taken together, these experiments highlight the flexibility of one important predator in the food web, where multiple environmental cues intersect to explain the role of habitat complexity in determining generalist predator accumulation.