Introduction

The amount of food eaten by a population of large mammalian herbivores affects their survival, reproductive success and, in the case of domestic stock, their economic performance. But intake by the herbivores also represents offtake from the pasture. Herbivores, by harvesting plant material from the pasture, have a feedback effect on biomass, growth and species composition of the pasture. Hence the herbivore and its rangelands pasture form an interactive relationship.

This chapter summarises the available information linking food intake of the major mammalian herbivores of the Australian sheep rangelands with food availability and identifies the factors, other than food availability, that modify intake. It then discusses the major feedback effects of this offtake on the vegetation.

The relationship between the food intake of a herbivore and vegetation biomass is known as the functional response. It can take a number of theoretical forms (Noy-Meir, 1975) but is most commonly expressed as an asymptoting function, often as a monotonically increasing curve (e.g. Allden & Whittaker, 1970; Arnold, 1975). At low biomasses the food intake of the herbivore is depressed because of the difficulties in locating and harvesting food. At high biomasses the intake of the herbivore is satiated and hence intake is relatively constant over a wide range of biomasses.