Functional response of optimally foraging herbivores

Abstract

We present a general functional response model for herbivores exploiting well defined food items such as ramets of trees, shrubs and many herbs. The basic assumption in our analysis is that the partial consumption of ramets is a patch exploitation process. This allows us to derive not only testable, but also biologically realistic, functional responses with respect to both ramet and biomass density available to the herbivore. It is essential to know both measures in order to properly examine plant-herbivore dynamics. In both cases the functional response is typically Type II (continuously decelerating). Because individual ramets are treated as patches, the functional response to a given total available biomass density is sensitive to both the number and size of ramets in the stand. This may have considerable effects on the plant-herbivore dynamics and on the growth form and life-history strategies of the plants under exploitation.