Structuring herbivore communities: the role of habitat and diet

This chapter tries to address the question “Why are there so many species?” with a focus on the diversity of herbivore species. We review several mechanisms of resource specialisation between herbivore species that allow coexistence, ranging from diet specialisation, habitat selection to spatial heterogeneity in resources. We use the ungulate community in Kruger National Park to illustrate approaches in niche differentiation. The habitat overlap of the ungulate species is analysed, continued with the overlap in diet and the spatial heterogeneity in resources. This focus on the constraints on species' exclusive resources is a useful tool for understanding how competitive interactions structure communities and limit species diversity. In explaining community structure of mobile animals, we argue that the existence of exclusive resources governed by spatial heterogeneity plays an important role. Tradeoffs between food availability and quality, food availability and predation risk, or food and abiotic conditions (different habitat types) may constrain competitive interactions among mobile animals and allow the existence of exclusive resources. We propose that body mass of the animals considered is crucial here as animals with different body mass use different resources and perceive spatial heterogeneity in resources differently. A functional explanation of the role of body mass in the structuring of communities is still lacking while the study of how much dissimilarity is minimally needed to permit coexistence between strongly overlapping species is still in its infancy. Nevertheless, a theoretical framework is emerging from which testable hypotheses can be generated.