Ecological Engineering by a Mega-Grazer: White Rhino Impacts on a South African Savanna Matthew S. Waldram, 1, * William J. Bond, 1 and William D. Stock 1,2 1 Botany Department, University of Cape Town, Private Bag, Rondebosch, Cape Town 7701, Republic of South Africa; 2 Centre for Ecosystem Management, Edith Cowan University, 100 Joondalup Drive, Joondalup, Western Australia 6027, Australia ABSTRACT 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 ef- fects of White Rhino on the grass sward, on other species of grazing mammals and on the movement of fire through the landscape. White Rhino main- tained 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 re- sulted 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 be- tween 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. Key words: megaherbivores; White Rhino; sa- vanna; grazing; fire; facilitation; keystone species; ecosystem engineers; Pleistocene extinctions. INTRODUCTION Fire and mammal grazers both consume grass and both are important modifiers of ecosystems, espe- cially in savannas where these two agents are often acting together. In principle, grazers could have marked indirect effects on their habitat by altering the fire regime. If grasses are grazed short enough, grazers could create biologically induced barriers to the spread of fire potentially altering the size, spa- tial distribution and frequency of fires in a land- scape. Grazer species capable of altering fire regimes in this manner could be considered ‘eco- system engineers‘ (Jones and others 1994). Their addition or extirpation from a landscape might have significant non-trophic impacts on ecosystem structure, function and biodiversity. Owen-Smith (1988) coined the term megaher- bivores for very large herbivores with an adult bodyweight greater than 1000 kg. He noted that large body size renders them largely immune to (non-human) predation while their bulk feeding allows them to tolerate food of a lower quality than Received 24 March 2007; accepted 5 November 2007; published online 30 November 2007. *Corresponding author; e-mail: matt@mattwaldram.com Ecosystems (2008) 11: 101–112 DOI: 10.1007/s10021-007-9109-9 101