APPARENT CANNIBALISM BY CHESAPEAKE GROUP NATICID GASTROPODS - A PREDICTABLE RESULT OF SELECTIVE PREDATION

Naticid gastropods of the Chesapeake Group of Maryland, like extant naticids, apparently were cannibalistic. This cannibalism did not result from the absence of bivalve prey or from the ineptitude of the predator, as some previous authors have suggested. Instead, predation on Chesapeake Group naticids was a predictable result of prey selection to maximize energy gain per foraging time. This study examines predation on Lunatia heros (530 specimens) and Polinices duplicatus (340 specimens) from the St. Marys Formation of the Chesapeake Group. Predation on naticids displayed the same characteristics as predation on bivalve prey, including selectivity of prey size and drillhole site. The two naticid species were differentially attacked, based on their relative cost-benefit ratios and escape sizes. Cannibalism is not anomalous; it is the expected result of selective predation, and is inhibited primarily by the high mobility of naticid prey.