Large herbivores and savanna heterogeneity

In taxonomic terms, the large herbivores (\u3e5 kg) of Kruger represent some 30 species drawn from three orders (Artiodactyla, Perissodactyla, Proboscidea) and seven families (Bovidae, Elephantidae, Equidae, Giraffidae, Hippopotamidae, Rhinocerotidae, Suidae). In functional terms there are two guilds: grazers (14 species), which feed mostly on monocots, and browsers (11 species), which feed mostly on dicots. An additional few switch back and forth between guilds (five species) depending on the quantity and quality of plant types available to them for food. A distinctive feature of each guild is that syntopic species tend to vary in body size (Owen-Smith 1985; McNaughton and Georgiadis 1986). For example, in any one part of Kruger during the dry season the browsing guild may include the world\u27s heaviest and tallest extant land animals (elephant [Loxodonta africana] and giraffe [Giraffa camelopardalis], respectively), together with a size-graded variety of others that would include some of the smallest ruminants (steenbok [Raphicerus campestris] and grysbok [R. melanotis]). Such an assemblage typically would represent a body mass range (in kilograms) spanning three orders of magnitude. Although this species richness is impressive in comparison with that of large herbivore assemblages in other biomes and on other continents, it is a typical (and indeed definitive) feature of the African savanna biome (Huntley 1982; Scholes and Walker 1993). Inevitably, questions about why so many large herbi-vore species evolved and how the extant ones coexist have formed a long-standing theme of inquiry in African savanna ecology (Lamprey 1963; Owen-Smith 1985; McNaughton and Georgiadis 1986; Vrba 1992). Here I extend that theme, drawing on research results from Kruger to explore how ungulate guild structure is influenced by savanna heterogeneity at multiple spatial and temporal scales