Herbivory can change the structure and spatial heterogeneity of vegetation. We ask whether all species of grazers in a savanna ecosystem can have this effect or whether megaherbivores (>1000 kg) have a ‘special’ role that cannot be replicated by other species of grazers. We performed a replicated landscape scale experiment that examined the effects of White Rhino on the grass sward, on other species of grazing mammals and on the movement of fire through the landscape. White Rhino maintained short grass (‘lawn’) patches in mesic areas (∼750 mm pa) with increases in grass sward height when they were removed. Other species of grazers were unable to maintain short grass communities when White Rhino were removed. In semi-arid areas (∼600 mm pa) other, smaller grazers were able to maintain short grass communities in the absence of White Rhino and sward height did not increase. White Rhino removals affected fire by increasing fuel loads and fuel continuity. This resulted in larger, less patchy fires. We propose that the White Rhino acts as an influential ecosystem engineer, creating and maintaining short grass swards, which alter habitat for other grazers and change the fire regime. These results indicate the existence of context-dependent facilitation between White Rhino and other grazers in mesic, but not in semi-arid, savannas. Such top down effects on the ecosystem may have been much more widespread before the extinction of large grazers in the Pleistocene.
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We thank Ezemvelo KZN Wildlife for permission to conduct this research and the management and research staff of Hluhluwe iMfolozi game reserve in particular for their help during the Zululand Grass Project (ZLGP) of which this study was a part. Special thanks must go to ZLGP staff and students for their contributions to the project. We also thank Norman Owen-Smith, Claudius van de Vijver and Sally Archibald for their inputs and Lindsey Gillson and Carla Staver for their comments on an earlier version of this article. Andrew Illius provided very helpful comments on several aspects of the study. This study was prompted by a seminal suggestion by Rob Slotow to WJB. Satellite images were provided by the Satellite Applications Centre, CSIR, Pretoria. The ZLGP was funded by both the Mellon foundation and the National Research Foundation of South Africa.
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Waldram, M.S., Bond, W.J. & Stock, W.D. Ecological Engineering by a Mega-Grazer: White Rhino Impacts on a South African Savanna. Ecosystems 11, 101–112 (2008). https://doi.org/10.1007/s10021-007-9109-9