Passive defensive traits are not good predictors of predation for in faunal reef bivalves

Predation is a key biotic interaction that shapes ecological communities. Defensive morphological traits are thought to improve prey survivorship, and knowing which traits aid survivorship is critical to understanding predator-prey dynamics and their impact on community composition. Paleontological studies that use optimal foraging theory and single species experiments suggest that shell size and thickness are traits that affect the outcome of mollusk drilling predation. We analyzed the effectiveness of these morphological traits using a tropical molluscan assemblage from the One Tree Reef lagoon (southern Great Barrier Reef, Australia). Shell mass, shape, thickness, and predation frequency were measured in five bivalve species (n = 804) constituting 80% of the predators' diet. Multiple regression determined that shell mass, shell thickness, and the interaction between the two were important predictors of predation. Drilling was more likely in thinner and larger individuals. However, support for the model that included species identity was markedly stronger, indicating that the morphological traits measured are not general predictors of predation across the five prey species we studied. That is, trait-only models are inadequate for explaining predator-prey dynamics at the community level. Alternatively, active behavioral defenses related to infaunality (like burrowing) appear to be stronger drivers of morphology in this system. Care should be taken when extrapolating results from experiments to communities or large temporal scales, as species with similar traits may not necessarily elicit the same response from predators.