Feeding mechanics of a trophic generalist and a specialist shark species: A comparison of diet, behavior and function

Ecomorphological studies investigate the relationship between the morphology of an organism and the environment. For feeding, this can be accomplished by a multi-level analysis of the diet, behavior and morphological function of the organism to predict the role of an organism with a community. Partitioning of resources within a community can often be determined by the degree of plasticity or degree of specialization used in resource acquisition by the members. This research studies the feeding ecology, behavior and function of a trophic generalist, spiny dogfish Squalus acanthias, and a trophic specialist, smooth-hounds Mustelus canis, from Narragansett Bay, Rhode Island to investigate the interaction of these predators within the environment. A specialist is expected to feed on a subset of available prey while a generalist will feed on a range of prey. A specialist will use a stereotyped behavior and jaw muscle function for prey capture and processing, however a generalist will modulate function and behavior dependent on prey type. These hypotheses were tested in performance tests of prey selection, variation of feeding behaviors and asynchronous activation of the jaw muscles. In the absence of interspecifics, spiny dogfish and smooth-hounds foraged optimally by selecting the prey item with the highest energetic return. However, smooth-hounds did not select crabs, the preferred natural prey. Spiny dogfish modulated prey capture and processing behaviors by choosing the behavior that best corresponds to prey type, as expected of a generalist. Smooth-hounds used stereotyped ram capture and stereotyped crush processing, indicative of a specialist. Spiny dogfish varied jaw muscle function between synchronous pairwise activation during capture to asynchronous activation during prey processing. In contrast, smooth-hounds used a stereotyped synchronous activation pattern. Based on these comprehensive analyses, spiny dogfish are generalist predators that exhibit behavioral and functional flexibility to feed on a variety of prey. Although smooth-hounds did not show the same dietary specialization they do in the wild, the stereotyped behavior and jaw muscle function indicates these sharks are specialist predators. In a natural environment, in the presence of other species, smooth-hounds are constrained to feed on a specialized resource using morphological, behavioral and functional specializations