When to live alone and when to live in groups : ecological determinants of sociality in the African striped mouse (Rhabdomys pumilio, Sparrman, 1784)

One aim in animal behaviour is to explain why and when animals live in groups. The main approach hits been to compare closely related gregarious and solitary species. Here, I discuss data of a medium sized, diurnal muroid rodent, the striped rnouse, which demonstrates a high level of intraspecific variability of its social system. In the arid Succulent Karoo, the social structure of the striped mouse is best described as a territorial group living Solitary forager with communal breeding and helpers at the nest. Groups can consist of up to 30 adult mice, i.e. four breeding females, one breeding male and their adult offspring. In contrast, the striped mouse is solitary in the mesic grasslands of South Africa, with females inhabiting intrasexually exclusive territories and male territories overlapping those of several females. Association between the sexes is limited to mating, and offspring leave their mother's territory as juveniles. Home ranges in the grasslands are much larger than in the Succulent Karoo. I suggest that the main ecological reasons for these differences in social organization arc food abundance, the availability Of Suitable nesting sites, and the possibility of sun-basking. Whether these ecological differences acted as selection pressures in the past that caused genetic differences and finally speciation (as proposed by a recent study), or whether these ecological differences lead to behavioural differences via an ontogenetic pathway, remains a topic for further research.