A diffuse coalition of the unwilling: Group size effects on social structure in yellow-bellied marmots (Marmota flaviventris)

Background/Question/Methods

Demographic variation, such as changes in population size affect group living conditions, thus creating new opportunities for individuals to socially interact. To understand how this variation in the social environment affects social structure, we used social network analysis to analyse affiliative behaviors of non-pup, female, yellow-bellied marmots (Marmota flaviventris). We examined four social attributes (outdegree, indegree, closeness centrality, and betweenness centrality) to measure social plasticity in response to group size variation.

Results/Conclusions

We found that in response to increases in group size, individuals increased their outdegree and indegree, but at a slow rate (slope << 1), showing that marmots experience constraints on sociality. We also found that individuals decreased their closeness centrality rapidly, suggesting that females lose influence over other members of the group as group size increases. Most of our betweenness measures were zero, a finding that suggests that the marmots live in small, cohesive groups. For those individuals with a non-zero betweenness score, we found that betweenness centrality decreased slowly as group size increased, a finding that suggests that there are substantial constraints on marmots transmitting information to others in large groups. It also is consistent with the hypothesis that most marmots are isolated from others and thereby are protected, to some extent, from socially transmitted parasites or pathogens. Like group size effects studied in other domains, formally considering group size effects on social network traits may shed novel light on constraints on sociality.