Why Predation Rate Should Not be Proportional to Predator Density

In most mathemetical models of population dynamics in ecological communities, the death rate of prey species is a linearly increasing function of the density of their predator(s). If antipredator behavior is incorporated into such models it becomes very unlikely that prey death rate is a linear function of predator density. In addition, it is possible for the prey death rate to decrease, rather than increase, as a function of the population density of its predator. Decreasing predation rates may be common when the prey organism is attempting to accumulate resources for growth or reproduction. Decreasing predation rates are less likely when the prey organism is attempting to minimize mortality. These results are earlier ones on indirect effects generated by optimal foraging (Abrams 1984, 1991a, b) suggest that higher order ineractions shoyld be extremely common in natural communities.