The ecology of ageing in wild societies: linking age structure and social behaviour

Abstract

The age of individuals has consequences not only for their fitness and behaviour but also for the functioning of the groups they form. Because social behaviour often changes with age, population age structure is expected to shape the social organization, the social environments individuals experience and the operation of social processes within populations. Although research has explored changes in individual social behaviour with age, particularly in controlled settings, there is limited understanding of how age structure governs sociality in wild populations. Here, we synthesize previous research into age-related effects on social processes in natural populations, and discuss the links between age structure, sociality and ecology, specifically focusing on how population age structure might influence social structure and functioning. We highlight the potential for using empirical data from natural populations in combination with social network approaches to uncover pathways linking individual social ageing, population age structure and societal functioning. We discuss the broader implications of these insights for understanding the social impacts of anthropogenic effects on animal population demography and for building a deeper understanding of societal ageing in general.This article is part of the discussion meeting issue 'Understanding age and society using natural populations'.

Keywords: age structure; ageing; senescence; social behaviour; social structure; sociality.

Figure 1.

A conceptual synthesis of how variation in demographic rates and properties, age structure and sociality might mutually affect one another.

Figure 2.

Social networks of hypothetical populations with different age structures following juvenile- or adult-biased removal, demonstrating the potential shifts in social structure as age structure is altered. The left column shows three initial social networks of 50 individuals with an equal (top), juvenile-biased (middle) and adult-biased (bottom) age distribution. Adults are shown in blue, subadults in green and juveniles in yellow. In these networks, we assume that the tendency to socialize decreases with age, i.e. juveniles are about six times more likely to socialize than adults. Underneath each social network, we present the network density (the number of existing connections divided by all possible connections), which gives a measure of how well individuals are connected. The central and right columns illustrate the hypothetical changes in network structure following juvenile-biased (central) or adult-biased (right) removal, i.e. under the juvenile-biased removal, juveniles had an 80% chance of being removed compared to adults and subadults (10% chance of removal each). In each case, 10 individuals were removed. Such effects of age distribution on social network structure should be assessed using empirical data from wild populations (see recent work [58,274]).

Figure 3.

Different mechanisms that could result in the same late-life changes in social selectivity with age. In each network, the focal individual is represented by the dark blue node.