Social Networks in Wild Asses: Comparing Patterns and Processes among Populations

Asiatic wild asses inhabit some of the most arid environments in the world. All live in fissionfusion societies, but demography varies and the deserts in which they live often differ in subtle ways. Characterizing details of social structure of wild ass populations has been a challenge and has made it difficult to determine causes and consequences of any differences that might exist. We use network theory to compare the social structures of two populations of Asiatic asses/onagers inhabiting the Negev desert, Israel and khur of the Little Rann of Kuch, India and show that populations differ in important structural ways that represent adaptive responses to variations in ecological demographic and phenotypic circumstances. Our analyses show that onagers inhabiting more variable environments then khur also live in larger, more cohesive groups than khur. Presumably networks with this structure facilitate the spread of information and foster cooperation. We also show that demography matters since social fragmentation increases as populations grow. Increases in the number of components in populations, reductions in the number of associates and diminished cliquishness within components, appear to be adaptive responses to integrating increasing numbers of individuals into social networks. We also find some support for the idea that social connectedness varies with phenotype. In our larger populations, non-lactating females who are most challenged in finding sparse feeding sites, are more selective than lactating females in their choice of strong associates. Presumably networks with this structure enhance foraging success by increasing information flow among like-minded individuals. As our study demonstrates, network analysis facilitates testing predictions about the cause of social structure and its impact on transmission processes.