Hierarchical resource selection by impala in a savanna environment



The factors that affect resource selection by a foraging herbivore can vary according to the resources or conditions associated with particular levels of organization in the environment, and to the scales over which the herbivore perceives and responds to those resources and conditions. To investigate the role of forage in this hierarchical process, we studied resource selection by a mixed-feeding large herbivore, the impala (Aepyceros melampus). We focussed on three spatial scales: plant species, feeding station and feeding patch. In paired sites where impala were and were not observed, we identified the plant species from which animals fed, the attributes of the plants, and the characteristics of the broader site. Across all three scales, plant species available as forage was central in determining resource selection by impala. At the species level, that effect was modified by the nutritional quality (greenness) and whether it was during a period of forage abundance or scarcity (season). At the feeding-station level, overall greenness and biomass of the station were important, but their effects were modified by the season. At the feeding-patch level, broader-scale factors such as the type of vegetation cover had an important influence on resource selection. The grass Panicum maximum was a preferred forage species and a key resource determining the locations of feeding impala. Our findings support the idea that selection by a foraging herbivore at fine scales (i.e. diet selection) can have consequences for broader-scale selection that result in observed patterns of habitat use and animal distribution.