William H. Romme

Landscape Heterogeneity and Ungulate Dynamics: What Spatial Scales are Important?

Ungulates make foraging choices at a variety of spatial scales, but the environmental parameters that are most important at various scales are not well known. Clearly, the spatial arrangement and density of vegetation influences the success of herbivores in finding food (Kareiva 1983 Risch et al. 1983 Stanton 1983 Cain 1985 Bell 1991). Theoretical studies suggest that organisms must operate at larger spatial scales (i.e., search a larger area) as resources become scarce and clumped across a landscape (O’Neill et al. 1988 Turner et al. 1993). In addition, the effectiveness of different foraging tactics may vary with the spatial distribution of resources (e.g.Cain 1985 Roese et al. 1991). However, understanding the responses of animals to spatial pattern at multiple scales is in its infancy (Kotliar and Wiens 1990 Kareiva 1990 Hyman et al. 1991 Ward and Saltz 1994) and remains a high priority for ecology (Lubchenco et al. 1991 Levin 1992). In this chapter, we synthesize results from three studies of winter foraging by ways that consumers create and respond to heterogeneity in the resources they use. Large, mobile herbivores discriminate among spatially variable food resources, thereby altering the structure of plant communities and the rates of ecosystem processes. Improving our knowledge of the responses of large herbivores to spatial heterogeneity can contribute to understanding the workings of many other ecological processes.