A community is a grouping of different organisms living together in a particular environment, whose interactions give that community its structure. The advantages of group living are many, and include earlier detection of predators (Sect. 7.1.3), but there may be a disadvantage in arid regions where food and other resources are especially scarce. Groups tend to confuse predators, dilute their effects on the population, and help individual animals from becoming victims (Bertram 1975). Social behaviour in African ungulates has been reviewed by Leuthold (1977) and social organization has been discussed by Delany and Happold (1979). Fluctuations often occur in the sizes of the groups and territories of desert mammals, especially carnivores, which show widespread and extensive flexibility in their social organization (Kruuk and Macdonald 1985; Mills 1990).