Consequences of Size-Selective Harvesting as an Evolutionary Game

Abstract

We model the evolution of prey body size in response to size-selective harvesting by humans. The manager ( = humans) selects a harvest rate and a threshold size of harvest (below which no smaller prey are harvested) so as to maximize yield. In response to the manager's harvesting regime, the adult size of the prey evolves to an evolutionarily stable strategy (ESS). Over a wide range of parameter values, the prey's ESS is only influenced by the manager's harvest rate and is independent of the manager's threshold size of harvest. Increasing the harvest rate selects for smaller adult prey. We contrast the harvest regime of an ecologically enlightened manager (one who only considers the ecological consequences of harvesting on the prey stock) with that of an evolutionarily enlightened manager who considers the consequences of harvesting on the prey's ESS adult size. The ecologically enlightened manager maintains a higher harvest rate and consequently selects for smaller adults. The evolutionarily enlightened manager uses an evolutionarily stable optimal harvest strategy (ESOHS, sensu Law and Grey 1989) that sacrifices increased yield in ecological time to maintain a larger adult prey size and higher yield in evolutionary time.