Foraging in a heterogeneous environment: intake and diet choice

Resource heterogeneity and its effects on consumers are crucial in the dynamics of landscapes with large herbivores. Although all elements necessary for a general quantitative theory of resource heterogeneity and foraging behaviour across spatial scales are available, such a theory has not been put forth yet. We need to learn what scales, what resources and what types of heterogeneity are relevant to conserve and manage landscapes with large herbivores. More specifically, what scales, variables and heterogeneity are important in determining intake and diet selection by large herbivores? Large herbivores interact with their resources through a series of nested processes such as ingestion, searching, digestion and resting, which define relevant scales. Empirical relationships between animal performance and average resource abundance are scale-specific. Extrapolations should be based on explicit models to change scale, and will benefit by using concepts and techniques from geostatistics. Heterogeneity and average herbage mass are frequently related, so that measured effects on intake cannot be unequivocally attributed to total herbage mass. Resource heterogeneity can affect intake and behaviour through nonlinearity of responses to local conditions, selectivity and changes of local functional response due to global conditions. In general, coarser resolution of heterogeneity allows a greater selectivity. These points are illustrated with examples from the literature and reinterpretation of published and unpublished data.