EFFECT OF THE PREDATOR-AVOIDANCE BEHAVIOR OF THE SEA-URCHIN, CENTROSTEPHANUS-CORONATUS, ON THE BREADTH OF ITS DIET

The sea urchin, Centrostephanus coronatus, exhibits a relatively broad diet. Evidence presented in this paper suggests that evolution of dietary breadth is favored by two mechanisms. First, individual urchins occur in habitat types that support somewhat different foods. Urchins consume principally the most preferred food where it is common but are forced to eat other food types where it is rare. Second, overgrazing by individual urchins reduces the local abundance of the most preferred food, thereby forcing them to add less preferred items to their diet. Previous work indicates that the escape behavior of Centrostephanus from its fish predator, Pimelometopon pulchrum, results in different individuals being exposed to different foods and in reduction of the size of urchin grazing ranges to the point that overgrazing occurs. Hence, by the two mechanisms discussed in this paper, the presence of the fish predator favors the broad diet of its sea urchin prey. © 1979 Springer-Verlag.