Relationship between mandibular morphology and predator efficiency in omnivorous and carnivorous carabid beetles

Mandubular morphology can constrain an organism’s ability to exploit available food resources. As a consequence, mouthpart morphology may provide a causal link between morphology and the ecological role of an organism in the community.  Specifically for a predator, mandibular morphology might dictate capture success and handling time of prey and thus govern its impact on trophic dynamics.  Strict omnivory requires mandibular adaptations that enable feeding on both plant and animal resources.  Moreover, the mandibular adaptations characteristic of omnivores may constrain their efficiency as predators, and thus affect their ability to suppress prey populations and promote trophic cascades. We examined differences in mandible morphology, capture success, and prey handling time between three omnivorous (seed and prey feeding) and three carnivorous (prey feeding) carabid beetle species. Two prey (caterpillar) species that differed in behavior (active versus sessile) and risk of predation were used to evaluate predator capture success and performance.  Omnivorous and carnivorous predators had distinct and consistent differences in mandible morphology.  The longer cutting edge and sharper tip of carnivore mandibles enhanced capture success and led to rapid prey mortality. These features were of particular benefit when capturing active prey. The lower capture efficiency of omnivores resulted in reduced weight gain per unit handling time. Results demonstrate that differences in capture efficiency and success between these two predator guilds is related to the functional morphology of their mandibles. With their greater capture success and killing efficiency, carnivores are better able to suppress prey populations and promote trophic cascades.