The Influence of Naticid Predation on Evolutionary Strategies of Bivalve Prey: Conclusions from a Model

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Abstract
An age-structured two-species predator-prey model was developed to explore the possible role of selective predation by naticid gastropods in the evolution of the energy allocation of their bivalve prey. The model describes prey fitness in terms of the amount of energy available for reproduction over a lifetime and describes predator fitness in terms of the net energy intake rate of the adult predator. Both species are considered to be age- and size-structured. Predation is size-dependent, and the predator is assumed to select prey in a manner that maximizes its net energy intake. Two evolutionary traits of the prey are considered: the age-dependent allocation of energy between reproduction and growth (X1) and the allocation of energy between overall growth and extra growth in shell thickness (X2). The results of the models are described in terms of prey phenotypic fitness landscapes as functions of predation intensity. These landscapes consist of prey fitness plotted as a function of the parameters, X1 and X2, governing the energy allocation strategies. As predation intensity increases from zero to a high value, the initial single optimum for prey fitness changes to a landscape of three local optima, representing alternative strategy types.