Abstract
BackgroundIn communal mammals the levels of social interaction among group members vary considerably. In recent years, biologists have realized that within-group interactions may affect survival of the group members. Several recent studies have demonstrated that the social integration of adult females is positively associated with infant survival, and female longevity is affected by the strength and stability of the individual social bonds. Our aim was to determine the social factors that influence adult longevity in social mammals.Methodology/Principal FindingsAs a model system, we studied the social rock hyrax (Procavia capensis), a plural breeder with low reproductive skew, whose groups are mainly composed of females. We applied network theory using 11 years of behavioral data to quantify the centrality of individuals within groups, and found adult longevity to be inversely correlated to the variance in centrality. In other words, animals in groups with more equal associations lived longer. Individual centrality was not correlated with longevity, implying that social tension may affect all group members and not only the weakest or less connected ones.Conclusions/SignificanceOur novel findings support previous studies emphasizing the adaptive value of social associations and the consequences of inequality among adults within social groups. However, contrary to previous studies, we suggest that it is not the number or strength of associations that an adult individual has (i.e. centrality) that is important, but the overall configuration of social relationships within the group (i.e. centrality SD) that is a key factor in influencing longevity.
Highlights
Group living occurs in many animal taxa, including invertebrates, fishes, birds and mammals [1], and is thought to offer protection against predators and to increase foraging efficiency, two factors which may have favored the evolutionary transition from solitary to group foraging [2]
We examined social network data for 34 group members of known age and who died as adults
We found that adult longevity was negatively associated with group size; defined as the mean group size in the years the specific individual belonged to the group
Summary
Group living occurs in many animal taxa, including invertebrates, fishes, birds and mammals [1], and is thought to offer protection against predators and to increase foraging efficiency, two factors which may have favored the evolutionary transition from solitary to group foraging [2]. Empirical studies of social mammals have shown that living in groups has significant consequences for reproductive success. [5]) and a non-linear relationship was demonstrated in other systems, with the largest and smallest groups showing the lowest reproductive success [6]. It has been suggested by Clutton-Brock et al [7] that the variation between group size and reproductive success is dependent on social system. Eviction of a specific individual may increase resources and survival of all other group members, and provide additional benefits to the dominant animals (e.g. reduce competition and increase fitness). Our aim was to determine the social factors that influence adult longevity in social mammals
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