Social organization in ungulates: Revisiting Jarman's hypotheses

Area of Science:

• Evolutionary Biology
• Animal Behavior
• Mammalogy

Background:

• Ungulates exhibit diverse social systems, prompting ecological explanations for their evolution.
• Jarman's (1974) scenario links resource distribution, habitat, and feeding style to ungulate social organization.
• This scenario, while influential, lacked rigorous phylogenetic testing.

Purpose of the Study:

• To test Jarman's (1974) hypotheses on ungulate social evolution using modern phylogenetic comparative methods.
• To investigate the influence of habitat and feeding style on ungulate social organization and group size.
• To examine the downstream effects of group size on mating systems and sexual size dimorphism.

Main Methods:

• Phylogenetic comparative analyses were performed on data from 230 ungulate species across ten families.
• Path analyses were used to assess direct and indirect evolutionary relationships between ecological factors and social organization.
• Statistical models were employed to test hypotheses regarding habitat, feeding style, body size, group size, mating systems, and sexual dimorphism.

Main Results:

• Habitat and feeding style significantly predict ungulate group size, with grazers in open habitats forming larger herds.
• Larger group sizes are associated with polygamous mating systems and pronounced sexual size dimorphism.
• Phylogenetic analyses confirmed that evolutionary shifts in habitat, feeding style, and body size drive changes in social organization.

Conclusions:

• Jarman's (1974) ecological scenario for ungulate social evolution is largely supported by phylogenetic evidence.
• Ecological factors directly and indirectly shape ungulate social systems, including group size, mating strategies, and sexual dimorphism.
• Further research is warranted to explore the broader applicability of these findings to other mammal groups.