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An integrative approach to specialization: relationships among feeding morphology, mechanics, behaviour, performance and diet in two syntopic snakes


A. Mori, Department of Zoology, Graduate School of Science, Kyoto University, Sakyo Kyoto 606-8502, Japan. Tel: +81 0 75 753 4075; Fax:+81 0 75 753 4075


Theoretically, dietary specialists should be morphologically, behaviourally and physiologically specialized to feed efficiently on a subset of the available prey. Yet, relatively few studies have actually tested each of these links in specialist predators, especially in terrestrial vertebrates. We address this issue here by comparing the relationships among feeding morphology, mechanics, swallowing duration and realized diet for a dietary generalist versus a specialist snake when feeding on seasonally abundant frog prey in syntopy. Previous work has shown that the dietary generalist (Elaphe quadrivirgata) consumes both frogs and hard-bodied prey such as lizards and snakes, whereas the specialist (Rhabdophis tigrinus) feeds primarily on bulky frogs. We thus predicted that the generalist should have a higher bite force to better manipulate hard-bodied prey, and the specialist should have a larger gape to better handle bulky frogs. Second, we predicted that the increased gape in the specialist should lead to shorter swallowing times and to larger consumed frog sizes in nature. As predicted, the specialist had relatively larger gapes and the generalist had relatively higher potential bite forces, and the specialist swallowed frogs faster than the generalist. Furthermore, field data showed that adult females of the specialist consumed significantly larger frogs than the generalist in syntopy. Overall, this study shows that dietary specialization is tightly linked to phenotypic specialization in a terrestrial vertebrate predator.