Scale Effects of Vegetation on Forager Movement and Seed Harvesting by Ants

The responses of animals to patch structure at different spatial scales influence how processes such as foraging and species interactions vary with spatial scale or translate across levels of organization. We investigated how seed harvesting by the western harvester ant (Pogonomyrmex occidentalis) was affected by vegetation structure in a shortgrass steppe ecosystem at levels of organization ranging from individual ants to populations and at spatial scales from 0.1 m 2 to 15 ha. In the first of two experiments, we used a hierarchical experimental design to assess the magnitude and variation in seed harvesting (1) among ant colonies in three pastures differing in livestock grazing intensity, (2) among colonies within pastures, and (3) among plant cover types within colonies