Social cohesion and intra-population community structure in southern Australian bottlenose dolphins (Tursiops sp.)

Abstract

Defining intra-population community variation in group living mammals provides insights about the impact of environmental, social, and anthropogenic factors on population sub-structuring. Here, we use generalised affiliation indices (GAIs) and social network analysis to investigate social cohesion and intra-population community structure of southern Australian bottlenose dolphins (Tursiops sp.) inhabiting Adelaide’s metropolitan coast in South Australia. Information on the sex and site fidelity of photographically identified individuals was used to investigate the potential link between these parameters and preferred affiliations at the population level. Genetic data was also used to investigate genetic relatedness within and between sex and communities. Overall, dolphins showed non-random associations, with preferred associates prominent amongst females and resident individuals. Dolphins were clustered into two social communities that showed little spatial overlap and were associated with different habitats: a northern, shallow-water community (NSWC) and a southern, deep-water community (SDWC). As expected, preferred associations were more prevalent within than between communities, and analyses of genetic relatedness indicated that dolphins, particularly females, were on average more related within than between communities. Social network metrics varied between communities, with the temporal stability of associations for both communities characterised by rapid disassociations and casual acquaintances. We suggest that these two dolphin communities likely arose due to a combination of ecological and socio-genetic factors. This study enhances our understanding of factors shaping social groups in long-lived mammals and our ability to manage human activities that can impact upon their behaviour and social structure. Determining how and why individual animals interact and form groups is important for understanding the evolution of sociality and designing management strategies for wildlife conservation. We investigated association patterns and social community structure in southern Australian bottlenose dolphins in Gulf waters of South Australia. Within the study area, dolphins were divided into two separate communities associated with different habitat types. Within these two communities, dolphins formed groups with particular individuals and mostly related individuals amongst females. These findings enhance our understanding of the factors shaping mammalian groups and our ability to manage human activities that can impact upon their behaviour and social structure.