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Large species generally occur at lower population densities than small species but, being larger, use more energy per individual. The balance between population density and energy use per individual determines how evenly community resources are shared by species of different size. Analyses of large data sets, covering a wide range of body sizes, have found that population metabolism (the product of population density and energy use per individual) scales either neutrally (Damuth 1981, 1987) or negatively (Peters 1983) with body mass. However, different scaling relationships may occur in certain communities within specific biogeographic regions. Brown and Maurer (1986) found that population metabolism scales positively with body mass among North American land birds, granivorous desert rodents, marine fishes, and perennial desert plants. A comprehensive study of the relationships between mammalian population density and body mass (Peters and Raelson 1984) indicates that population metabolism scales positively with body mass among "smaller tropical" herbivores (cxM026), "larger tropical" herbivores (cx M045), and "larger tropical" carnivores-omnivores (cxM028) but not among North American species (herbivores, cxM0 09; carnivores-omnivores, xMm-0.39) We present results confirming that among African savanna herbivores, population metabolism scales positively with body mass. That is, larger species use a disproportionately larger share of local resources. We also present a hypothesis to explain this, on the basis of patterns of habitat use. We analyzed census data for mammalian herbivores (-4 kg) from 11 African national parks or wildlife reserves within the savanna biome. Areas varied from 75 km2 to 19,500 km2. Population metabolism was calculated as the product of mean population density, mean individual body mass, and mass-specific metabolic rate (assumed to scale as M-0.25; Kleiber 1961). The combined data from these parks show that population metabolism increases significantly with body mass (table 1). However, a tendency to undercount smaller species could have influenced this result. Hence, we also examined ungulate populations estimated for the Umfolozi Game Reserve in South Africa, where aerial census data were corrected with intensive ground-based counts. A similar relationship between population metabolism and body mass was found. Finally, we considered the highest local densities reported from specific studies in areas favored by each species. Our analysis (table 1) shows that, among large herbivorous species in African savanna ecosystems, population metabolism increases approximately in relation to M045s. This relationship is confirmed by Damuth's (1987) data, in which population metabo-

Body Size, Population Metabolism, and Habitat Specialization Among Large African Herbivores