The (surprising) importance of males in a matrilineal society: behavioural insights from a topological knockout study

Social group structure often has consequences for individual fitness and ecological and evolutionary processes, but group structure is not fixed because of demographic processes: individuals die, disperse or are recruited into social groups. Thus, it is important to understand how demographic social roles and the loss of individuals with different roles modify group structure. We studied yellow-bellied marmots, Marmota flaviventer, and performed a series of statistical/topological knockouts on observed marmot social networks to investigate how the social roles of individuals from specific age–sex categories (adult/yearling, males/females) contribute to group social structure and to ask whether the loss of different roles has varying structural effects. We focused on five central aspects of overall social structure: density, the global clustering coefficient, reciprocity, global degree centrality and the coefficient of variation of strength. Somewhat surprisingly, given that marmots live in matrilines, our knockout results suggested that males played a key role in shaping networks: yearling males were a key cohesive element and adult males were central players in agonistic networks. Thus, social networks are dynamic and their structure is shaped in the interplay of demographic processes and individual social behaviour.