The Developmental Response of Predators to Changes in Prey Density

If a predator eats more prey at higher prey densities, grows more as a consequence, and then kills more prey because of its larger size, this produces a developmental response to prey density. In its functional response a predator sea shore snail caused a decreasing percentage mortality as prey (barnacle) density increased (type 2 response). This causes instability in prey numbers. However, when account was taken of the developmental response in a hypothetical pseudosnail, the prey mortality caused over a year by a single—predator as a function of prey density, was different from that expected on the basis of the functional response alone. There is a tendency for the mortality to be a fairly constant percentage of prey density over a rather large range of prey densities. This results in the reduction of the destabilizing effect. Problems of integrating these responses with the numerical response and of generalizing the results are discussed.