Predation by Miocene Gastropods of the Chesapeake Group: Stereotyped and Predictable

Abstract

Extant shell-drilling naticid gastropods are highly selective predators, choosing prey in accord with a model based on relative cost:benefit ratios (Kitchell et al., 1981). However, prey are not evaluated based on individual experiences; drilling instead follows stereotyped rules that are not modified by training. Stereotyped behavior of extant naticids includes selectivity of drillhole site on the prey shell and prey size. Such stereotypy may have developed over geologic time. This study determines whether predation by Miocene naticid gastropods of the Chesapeake Group was stereotyped and predictable by the Kitchell et al. (1981) model. Predation by Chesapeake Group naticids was highly selective with respect to prey size and drillhole site. This stereotypy increased the probability of successful predation by the naticids. Prey taxa showing the greatest selectivity of site and size also displayed the greatest rates of successful predation. Corbula exhibited the least size and site specificity and was preyed upon least successfully. Corbula is also the taxon for which predation was not readily predictable by the Kitchell et al. (1981) naticid prey preference model. The poor predictability of predation on Corbula is attributed to the presence of a conchiolin layer within the shell that may act as a deterrent to predation. Predation on four other prey genera was predictable by the model; naticids chose prey with the lowest cost:benefit ratios. Stereotypy of predation thus appears to have been well developed in the Miocene.