Diet overlap between grevy's zebra (equus grevyi) and selected livestock in Southern Samburu Kenya

Abstract

Population of Grevy's zebra has declined drastically in the last four decadesCurrently, the population in the wild is estimated to be less than 3,000 and International Union for Conservation of Nature (IUCN) has thus listed it as endangered species. Among the main causes of the decline are; hunting, competition with grazing animals, habitat destruction and human disturbance at critical water sources. Although several studies aimed at understanding and mitigating these threats have been carried out, the threats posed by forage competition with livestock have not been adequately addressed. The aim of the present study was therefore to evaluate the diet overlap between Grevy's zebra and livestock in southern Samburu. The study covering both the wet and dry seasons was carried out between April and December 2009 . To estimate forage availability, the composition, abundance and diversity of forage species were determined by quadrat technique while diets of both Grevy's zebra and livestock was determined by monitoring their grazing behavior. Dietary components of Grevy's zebra were further confirmed by carrying out micro- histological analysis of their fecal matter. Graminoids were the most abundant with a mean prominence value (PV) of 14.16 while browses came second with a mean PV of 8.35. Forbs mainly occurred in wet season and had a mean PV of 5.44. Graminoid species contributed the highest proportion of the Grevy's zebras diet (78%) followed by browse species (22%). Donkeys preferred browse species (88.9%) while sheep and cattle preferred grasses (55.8% and 74.9% respectively) to other categories of forage in dry mid and wet seasons. The proportions contributing to their diets changed seasonally. High diet overlap indices were recorded between Grevy's zebra and cattle (0.97) and Grevy's zebra and sheep (0.88). The diet overlap index between Grevy's zebra and the donkeys was comparatively lower (0.34). The seasonal overlap indices showed a decline through dry (0.76), mid 0.74) and wet (0.70) seasons implying that the competition for food is severe when its availability is limited. Higher prominence values for all forage categories in wet season confirms the abundance of forage in rainy season while proportions of forage categories making the diets of each of the animals studied confirms that; Grevy's and cattle are mainly grazers, sheep are intermediate feeders and donkeys are browsers. From the study findings, it can be concluded that a higher potential for inter-specific competition for food niche exists between Grevy' and cattle than between the former and sheep. Donkeys pose least potential for competaion, Formulation and implementation of policies that will facilitate range separation between cattle and Grevy's zebra and research on pasture improvement methods would be the right steps towards saving the threatened Grevy's zebra in the southern Samburu.