Quantifying the influence of sociality on population structure in bottlenose dolphins

Abstract

Summary 1.The social structure of a population plays a key role in many aspects of its ecology and biology. It influences its genetic make-up, the way diseases spread through it and the way animals exploit their environment. However, the description of social structure in nonprimate animals is receiving little attention because of the difficulty in abstracting social structure from the description of association patterns between individuals. 2. Here we focus on recently developed analytical techniques that facilitate inference about social structure from association patterns. We apply them to the population of bottlenose dolphins residing along the Scottish east coast, to detect the presence of communities within this population and infer its social structure from the temporal variation in association patterns between individuals. 3. Using network analytical techniques, we show that the population is composed of two social units with restricted interactions. These two units seem to be related to known differences in the ranging pattern of individuals. By examining social structuring at different spatial scales, we confirm that the identification of these two units is the result of genuine social affiliation and is not an artefact of their spatial distribution. 4. We also show that the structure of this fission-fusion society relies principally on short-term casual acquaintances lasting a few days with a smaller proportion of associations lasting several years. These findings highlight how network analyses can be used to detect and understand the forces driving social organization of bottlenose dolphins and other social species.

Evidence for social role in a dolphin social network

“…They can help synchronising the activities of the school without advertising it to non-school members. There is no sign of complete segregation of social units in bottlenose dolphins (13,27,32). The social structure of the Doubtful Sound bottlenose dolphin population is such that a large proportion of individuals within schools (41%) spent a significant amount of time together, hence it would be advantageous to not only have a signal that would allow activity synchronisation but also would not allow this synchronisation to be advertised outside the school (24).…”

Disentangling social networks from spatiotemporal dynamics: the temporal structure of a dolphin society

“…These modules may correspond to different functional social units (e.g. Lusseau et al 2006;Guimarães et al 2007), a largescale level of complexity within the networked system (Newman 2011).…”

Individual Recognition

“…Photo-identification of natural markings is increasingly being used to collect data on individual animals for application to demographic studies (Thompson et al, 2000;Lusseau et al, 2006;Bradshaw et al, 2007). Although information obtained from photo-identification is highly valuable (Hammond, 1990;Blackmer et al, 2000), processing data in large catalogues can be labour-intensive and subject to human error (Kelly, 2001).…”

“…between islands or across the Mediterranean basin and how this impacts micro and macro population dynamics. The permanency of photographic data not only permits retrospective analyses as research objectives evolve, but also provides an opportunity to investigate other parameters that may also influence species conservation management and ecological risk assessments such as site fidelity, patterns of interaction, physical condition, health indicators and the impact of anthropogenic activity (Burger and Garber, 1995;Bennett et al, 1999;Pettis et al, 2004;Lusseau et al, 2006).…”

“…The ability to identify individuals within a population is often a starting point for ecological and conservation studies (Thompson et al, 2000;Sibly et al, 2005;Lusseau et al, 2006;Bradshaw et al, 2007;McMahon et al, 2007). Realistic estimates of population size and life history parameters are central to effective wildlife management, but are often difficult to measure in long-lived and elusive migratory marine vertebrates (Caughley, 1994).…”