Predators, facilitators, or both? Re-evaluating an apparent predator–prey relationship

Abstract

Predators and prey are occasionally observed to comingle in close proximity on coral reefs. Both lethal and non-lethal (i.e. behavioral) effects of predators on prey are well documented. However, observations of apparent predator-prey interactions between the piscivorous twinspot snapper Lutjanus bohar and the herbivorous surgeonfish Acanthurus triostegus suggest that the nature of their association may be context-dependent. The context-dependent nature of some species interactions is well-known, and in some cases a single species has been shown to act as both preda- tor and facilitator to its prey. We present incidental in situ observations suggesting that, in the context of voraciously grazing schools of A. triostegus, this species pair may also engage in a facultative mutualistic relationship. Specifically, we propose that within this context, both species may indirectly derive a benefit through changes in the behavior and/or density of territorial damselfishes driven by both L. bohar and A. triostegus. We provide prescriptions for rigorously testing this hypothesis and suggest that re-evaluation of this, and possibly other, ostensibly exclusive predator-prey pairs in marine systems may reveal unexpected relationships. Given the relative lack of examples of such interactions involving the same predator acting as both facilitator and predator from marine versus terrestrial systems, coupled with this preliminary evidence, we propose that this topic is ripe for exploration.