Body size and measurement of species diversity in large grazing mammals

Species are by de¢nition di¡erent from each other. This fact favours ranking rather than additive indices. However, ecologists have measured species diversity in terms of species richness, orbycombining species richnesswith the relative abundance of species within an area. Both methods raise problems: species richness treats all species equally, while relative abundance is not a ¢xed property of species but varies widely temporally and spatially, and requires a massive sampling e¡ort. The functional aspect of species diversity measurement may be strengthened by incorporating di¡erences between species such as body size as a component of diversity. An index of diversity derived fromameasure of variation in body size among species is proposed for large grazing mammals.The proposed diversity index related positively to species abundance, indicating that the use of body size as a surrogate for diversity is adequate. Because the proposed index is based on presence or absence data, the expensive and time consuming counting of individuals per species in each sampling unit is not necessary.