Guiana dolphins form social modules in a large population with high ranging overlap and small demographic changes
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.
Animal social relationships are dynamic, usually reflecting group living trade-offs. Simultaneously, they are influenced by the opportunities individuals have to interact. Group membership—co-occurrence in the same space and time—is the most used proxy for describing animal social relationships. Therefore, if the spatiotemporal context is not accounted for, the resultant social structure can be misrepresented. Here, we explore the social patterns of Guiana dolphins explicitly accounting for space use and temporal demographic changes. We show the largest population of Guiana dolphins displays fission-fusion dynamics, while it is structured into four distinctive sets of individuals. By accounting for asocial processes, we suggest such social modules were unlikely to result from unequal opportunities to interact but rather involved social preferences among individuals. Our findings highlight the importance of separating asocial from social processes while studying animal societies.
KeywordsSotalia guianensis Social network Space use Social structure Population turnover
We thank the Instituto Boto Cinza and their volunteers for the logistical support and assistance in the fieldwork; the two anonymous reviewers for the insightful comments that helped us improved our work; and E. Zwamborn for proofreading the manuscript. This study was carried out as part of a M.Sc. thesis in the Graduate Program in Ecology at the Universidade Federal de Santa Catarina, Brazil.
Compliance with ethical standards
All procedures performed in studies involving animals were in accordance with the ethical standards of the institution or practice at which the studies were conducted.
LBC was supported by CAPES (Brazil) scholarship. MC was supported by doctoral scholarships from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq Brazil) and Killam Trusts (Canada); LF received funds from CAPES; and PCSL received funds from CNPq.
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
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