Social organization in ungulates: revisiting Jarman's hypotheses

Ungulates (antelopes, deer and relatives) have some of the most diverse social systems among mammals. To understand the evolution of ungulate social organisation, Jarman (1974) proposed an ecological scenario of how distribution of resources, habitat and feeding style may have influenced social organisation. Although Jarman’s scenario makes intuitive sense and remain a textbook example of social evolution, it has not been scrutinised using modern phylogenetic comparative methods. Here we use 230 ungulate species from 10 families to test Jarman’s hypotheses using phylogenetic analyses. Consistently with Jarman’s proposition, both habitat and feeding style predict group size, since grazing ungulates typically live in open habitats and form large herds. Group size, in turn, has a knock-on effect on mating systems and sexual size dimorphism, since ungulates that live in large herds exhibit polygamy and extensive sexual size dimorphism. Phylogenetic confirmatory path analyses suggest that ev...