The adaptive value of sociality in mammalian groups

Abstract

According to behavioural ecology theory, sociality evolves when the net benefits of close association with conspecifics exceed the costs. The nature and relative magnitude of the benefits and costs of sociality are expected to vary across species and habitats. When sociality is favoured, animals may form groups that range from small pair-bonded units to huge aggregations. The size and composition of social groups have diverse effects on morphology and behaviour, ranging from the extent of sexual dimorphism to brain size, and the structure of social relationships. This general argument implies that sociality has fitness consequences for individuals. However, for most mammalian species, especially long-lived animals like primates, there are sizable gaps in the chain of evidence that links sociality and social bonds to fitness outcomes. These gaps reflect the difficulty of quantifying the cumulative effects of behavioural interactions on fitness and the lack of information about the nature of social relationships among individuals in most taxa. Here, I review what is known about the reproductive consequences of sociality for mammals.

Intraspecific variation in social organization by genetic variation, developmental plasticity, social flexibility or entirely extrinsic factors

“…While the occurrence of intraspecific variation in social organization has received significant attention and acknowledgement recently, the focus has been on the associated ecological factors [13,16,17]. Additionally, we need to understand the different proximate and evolutionary mechanisms that arise from these ecological factors.…”

“…Here, I focus on the social organization, i.e. the composition of groups, because this is the parameter most easily measured in field studies, and because it influences the mating system, the social structure and thus the social system [6,13].…”

Coping with the cold: predictors of survival in wild Barbary macaques, Macaca sylvanus

“…The strength of social bonds that an individual has with other group members is thought to affect individual fitness [2,3]. However, empirical evidence on the link between sociality and fitness is extremely scarce in the literature.…”

Explaining brain size variation: from social to cultural brain

“…Developed to explain variation order in relative brain size among mammalian orders and within primates, the hypothesis argues that large brains are adaptations for dealing with the complexities of social life. Several studies have documented the remarkably sophisticated understanding of the social world in primates [5], as well as some birds [6]. Although the originally used adjective 'Machiavellian' seemed to stress the competitive aspects of social life, the hypothesis equally applies to cooperative aspects, such as social learning, cooperation and coordination [7,8].…”