Evol Ecol Res 13: 237-252 (2011) Full PDF if your library subscribes.
Facilitation between bovids and equids on an African savanna
Wilfred O. Odadi1,2,3, Meha Jain1,4, Sipke E. Van Wieren5, Herbert H.T. Prins5 and Daniel I. Rubenstein1,2
1Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, USA, 2Mpala Research Centre, Nanyuki, Kenya, 3African Wildlife Foundation, Nairobi, Kenya, 4Department of Ecology, Evolution and Environmental Biology, Columbia University, New York, USA and 5Resource Ecology Group, Wageningen University, Wageningen, Netherlands
Correspondence: W.O. Odadi, Mpala Research Centre, PO Box 555, Nanyuki, Kenya.
Background: Equids, especially zebras and donkeys, and cattle (bovids) share habitats in many savanna ecosystems in Africa. The issue of competition for food between these ungulate guilds remains largely unresolved. Resolving it will provide insights into how wild zebra are likely to interact with cattle on shared landscapes and suggest best practices for cattle owners who must decide whether to tolerate wild ungulates, some of which are severely threatened (e.g. Grevy’s zebra, Equus grevyi).
Aim: Determine whether an equid and a bovid compete in a semi-arid savanna in Kenya.
Organisms: Boran cattle (Bos indicus) and donkeys (Equus africanus asinus) – the latter as surrogates for zebras.
Methodology: Experiments to measure performance (weight gains), bite rates, diet quality (digestible organic matter and crude protein), and gastrointestinal worm burdens (parasite egg count per unit weight of faeces) of the two ungulate species when herded separately (single species) or together (mixed species). We used two stocking levels: low-density (one animal per 7 ha), a level typical of commercial ranchers; and high-density (one animal per 2 ha), a level typical of pastoral herders.
Principal findings: When herded together, both species gained more weight, had higher bite rates (especially at low stocking density), and selected diets with a more favourable balance between digestible organic matter and crude protein, than when herded separately. In addition, parasite egg output in faeces of donkeys was reduced by 14–35% following shared foraging with cattle.
Conclusion: Cattle (a ruminant) and donkeys (hindgut fermenters, closely related to zebras) showed no evidence of competion with each other. Rather, our results show a facilitative, rather than a competitive, interaction between them.
Keywords: bite rate, bovids, cattle, competition, crude protein, digestible organic matter, donkeys, equids, facilitation, gastrointestinal parasites, grazing strategies, grazing succession, mutualism, weight gain, zebras.
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