Background/Question/Methods Habitat complexity is often viewed as an important factor that can reduce the impact of predators on prey by providing refugia for prey.  Sit-and-wait predators, however, may perform better in complex environments that provide more perches or hiding places for the predator.  Although natural environments are composed of many structural elements (types of habitat complexity) few researchers have examined how multiple types of habitat complexity affect predator-prey interactions.  We conducted an experiment in artificial ponds to examine how different types of habitat complexity (amount of benthic leaf litter versus amount of emergent vegetation) influence the effect of a sit-and-wait top predator (larval dragonflies; Anax spp.) on fitness components of an intermediate predator (larval salamanders; Ambystoma opacum).  We expected that 1) increasing amounts of emergent vegetation will enhance the effect of Anax on A. opacum fitness components by increasing perch sites for Anax to hunt from, 2) increasing amounts of litter will reduce the effect of Anax on A. opacum fitness components by providing benthic refugia for A. opacum, and 3) the effect of emergent vegetation on the foraging success of Anax will be greatest in ponds with less leaf litter due to the fact that there is less refuge space.
Results/Conclusions We observed a trend in ponds with no Anax for A. opacum to have higher survivorship when there was a low amount of leaf litter present in the pond.  Anax reduced A. opacum survivorship but the extent of reduction depended on the amount and type of habitat complexity present.  Specifically, increasing amounts of emergent vegetation in ponds with low amounts of litter enhanced the negative effect of Anax on A. opacum survival.  Increasing amounts of emergent vegetation in ponds with a high abundance of leaf litter, however, caused non-linear changes in the effect of Anax on A. opacum.  Although a high abundance of emergent vegetation in ponds with a high abundance of litter enhanced the effect of Anax on A. opacum survival, a low abundance of emergent vegetation in ponds with a high abundance of litter reduced the effect of Anax on A. opacum survival.  Our study found that the amount of habitat complexity may have unexpected effects on intermediate predator performance in the absence of top predators.  Our results also demonstrate that different types of habitat complexity can alter predator-prey interactions in different ways – some forms of complexity benefit the predator while other forms benefit prey.