Resource partitioning along multiple niche dimensions in differently sized African savanna grazers

Authors


E. J. Kleynhans, Centre for Ecological and Evolutionary Studies, Univ. of Groningen, Kerklaan 30, NL–9751 NN Haren, the Netherlands. E-mail: kleynhan@zoology.ubc.ca

Abstract

Resource partitioning among mammalian savanna herbivores is thought to be predominantly driven by differences in body size. In general, large herbivore species utilize abundant low quality forage while small herbivores focus on scarcer high quality food items. However, in a natural system other factors such as digestive strategy, season and the presence of megaherbivores (body size > 1000 kg) are likely to complicate allometric predictions. Non-ruminants are probably better able to cope with abundant low quality food than ruminants of the same size causing a non-ruminant to act ‘larger’ than allometrically predicted. Also, the effect of alternating seasons with high and low food availability on diet choice and hence the competitive interactions between co-occurring herbivores is still poorly understood. Lastly, how megaherbivores deviate from allometric predictions (based on smaller species) is still not well quantified.

In this study we examine resource partitioning among three ruminant and three non-ruminant grazers: impala, wildebeest, buffalo, warthog, zebra and white rhinoceros (megaherbivore) in the savanna of Hluhluwe iMfolozi Park, South Africa. We analysed habitat and diet overlap, specifically grass species (something not commonly investigated) and grass height eaten, in both the wet and the dry seasons. We found that habitat utilization differences among the species were generally small and did not vary between seasons. Diets within feeding patches overlapped during the wet season but highly diverged during the dry season. Body mass differences among species explained their dry season resource partitioning for all species except for comparisons with the megaherbivore (white rhino), while differences in digestive strategy were not related to niche overlap in either season. We conclude that savanna herbivores in this system coexist mostly through body size-driven resource partitioning in the dry-season, with the exception of the white rhino (megaherbivore).

Ancillary