The past decade has seen the resurgence of studies of niche differentiation in animal communities, owing largely to developments in stable isotope analysis. Using this approach, increasing emphasis has been placed on which organizational levels are most important for niche partitioning, with many studies supporting the concept of differentiation at the individual (intra-specific) level. Amongst large mammal herbivores, we do not expect high levels of between-individual niche partitioning, owing to a combination of nutritional and ecological constraints, but species’ niches are expected to shift i) between populations across habitats and ii) between species. We used, along with other metrics, variance components analysis to analyse isotopic niche variations in contemporary and historical assemblages of free-ranging herbivores across a variety of southern African savannas and grasslands. We tested whether a general pattern of isotopic niche differentiation existed, and at which level of organization.
Results/Conclusions
In virtually all contemporary assemblages, inter-specific differences in carbon isotope niches accounted for most of the variation in our data. Therefore, partitioning of niches across species emerges a general pattern, occurring even within trophic guilds, i.e. within browsers or grazers. In these assemblages, levels of inter-specific partitioning increased as a function of species richness. However, the opposite trend emerged in more speciose Pleistocene fossil assemblages: here, species’ had generally broad niches, and isotopic niche diversity between species was less evident. Most estimates suggest our study area was more productive during the Pleistocene than during the Holocene, which, therefore, supports the view that niche differentiation is only important for community assembly in resource-limited environments.