Guiana dolphins form social modules in a large population with high ranging overlap and small demographic changes

Abstract

The number and strength of social relationships are generally the products of group living trade-offs. However, they can be at least partially influenced by asocial factors such as the spatiotemporal opportunities for individuals to interact. We explored the social patterns of the largest population of Guiana dolphins—from dyadic interactions to the large-scale structure of their social network—considering their use of space and demographic changes during 6 years. We found that their society displays fission-fusion dynamics, characterized mainly by brief associations among individuals, and is weakly structured into four social modules. Spatial use and temporal demographic changes had minor effects on the patterns of associations among individuals. This suggests that the social modules unlikely represented spatiotemporal aggregations of individuals due to resource availability but rather involved social preferences among individuals. We show that Guiana dolphins can form social modules even in a large population with high ranging overlap and few demographic changes over time, although these social boundaries are blurred by the dynamic nature of the social relationships. Our findings illustrate and support the recent claims for the need of taking asocial processes in account when studying social structure of any animal species.