Multiple prey effects: Agonistic behaviors between prey species enhances consumption by their shared predator

摘要

Multiple prey species may affect consumption by their shared predator in a non-additive fashion which cannot be predicted by summing pairwise predator-prey interactions within food webs. By manipulating prey species richness and identity in experimental mesocosms, we sought to explore the effects of interspecific prey interactions between pinfish Lagodon rhomboides and pigfish Orthopristis chrysoptera, and between blue crabs Callinectes sapidus and common mud crabs Panopeus herbstii on the consumption rates of a shared predator species, gulf toadfish Opsanus beta. We also determined the effects of these interactions on the survivorship of the prey species as mediated by the predator. In both fish and crab prey trials, interspecific interactions between multiple prey increased the overall consumption rate of O. beta, and in each case, one prey species was harmed (decreased survivorship) while the other prey species was not significantly affected by these interactions (all relative to single-prey treatments). In trials run with fish prey, behavioral observations revealed that L. rhomboides aggressively chased O. chrysoptera out of a seagrass refuge and into a surrounding sand matrix where O. beta foraged, thus increasing O. chrysoptera vulnerability to predation. In trials run with crab prey, C sapidus failed to reduce their activity in the presence of O. beta. In addition, P. herbstii displaced C. sapidus from the seagrass refuge in mixed prey treatments, and so these conspicuous behaviors primarily occurred in the unstructured sand habitat where C. sapidus were more vulnerable to predation. We conclude that multiple prey effects, including those involving risk-enhancing, agonistic interactions between prey, can be important determinants of predator-prey outcomes. This may be especially true when refuge space is limited.