Competition and compensation among cattle, zebras, and elephants in a semi-arid savanna in Laikipia, Kenya

Competition and compatibility between livestock and wildlife in Africa has been a point of considerable speculation, with implications for conservation. However, controlled replicated experiments are lacking. Here we report on the results of a long-term exclosure experiment in Laikipia, Kenya, in which different guilds of large mammalian herbivores have been independently manipulated since 1995. In plots from which cattle were excluded, the density of zebra dung in 2000 was on average 46% greater than in control plots. This was due to differential zebra use, and not to differential rates of dung removal (by dung beetles or other factors). Vegetation data indicate that cattle fully compensate for the absence of wildlife; all plots accessible to cattle had similarly low grass cover. However, wildlife do not fully compensate for the absence of cattle; plots with only wildlife had more grass cover than plots accessible to cattle. Zebra dung density was strongly correlated with total grass cover, suggesting that zebras are effectively tracking resource abundance. There is also evidence of pair-wise competition between cattle and elephants, and between elephants and zebras. The strong competition between cattle and zebras appears to be mitigated by the presence of elephants. A significant cattle x elephant interaction on the abundance of zebra dung indicates that elephants reduce the negative effects of cattle on zebras. In the presence of cattle, elephants facilitate the abundance of zebra, apparently by suppressing resource extraction (bite rates) by cattle. The precise mechanism for this indirect facilitation is not clear, but it may be related to the demonstrated reduction in forb cover associated with elephant presence.