Role of forage, habitat and predation in the behavioural plasticity of a small African antelope

Summary Ecological influences on social organization can best be measured by comparing populations of a socially variable species living in different environments. We examined causes of variability in social behaviour in a socially plastic small antelope, the oribi, Ourebia ourebi Zimmermann, in Ghana, West Africa. In total, 161 individually identified oribi were observed at five sites along an ecological gradient through dry and rainy seasons. Behavioural observations and ecological data were used to test the relative influence of forage abundance and quality, habitat structure and predation pressure on female dispersion and male social behaviour. Of nine ecological variables that were quantified, forage abundance and quality accounted best for variation in female dispersion among and within study populations. Specifically, female oribi formed larger groups and had smaller ranges where dry season forage was relatively abundant and low in fibre. Male territorial behaviour differed among sites and was related to female home range size. Males were most active in territory maintenance where females had small home ranges, and males defended a female rather than a territory where females ranged widely. These results show that variation in social organization among oribi subpopulations in Ghana reflects female responses to the availability and quality of dry season food resources and male responses to the variable distribution and ranging behaviour of females.