Individual and ecological heterogeneity promote complex communication in social vertebrate group decisions

Abstract

To receive the benefits of social living, individuals must make effective group decisions that enable them to achieve behavioural coordination and maintain cohesion. However, heterogeneity in the physical and social environments surrounding group decision-making contexts can increase the level of difficulty social organisms face in making decisions. Groups that live in variable physical environments (high ecological heterogeneity) can experience barriers to information transfer and increased levels of ecological uncertainty. In addition, in groups with large phenotypic variation (high individual heterogeneity), individuals can have substantial conflicts of interest regarding the timing and nature of activities, making it difficult for them to coordinate their behaviours or reach a consensus. In such cases, active communication can increase individuals' abilities to achieve coordination, such as by facilitating the transfer and aggregation of information about the environment or individual behavioural preferences. Here, we review the role of communication in vertebrate group decision-making and its relationship to heterogeneity in the ecological and social environment surrounding group decision-making contexts. We propose that complex communication has evolved to facilitate decision-making in specific socio-ecological contexts, and we provide a framework for studying this topic and testing related hypotheses as part of future research in this area. This article is part of the theme issue 'The power of sound: unravelling how acoustic communication shapes group dynamics'.

Keywords: communication; complexity; group decision-making; heterogeneity.

Figure 1.

(a) Ecological heterogeneity is defined broadly as the spatial variation in land cover and vegetation (habitat) [9,10], the temporal variation of resources and climate (environment) [–13] and species diversity [14,15]. For example, while grasslands (pictured in a(i), licensed under CC BY-SA) have complex height structures (within individual patches of grassland) and there is variability between the patches (i.e. different species), we consider grassland to have low ecological heterogeneity from the perspective of a grazing ungulate herd. In contrast, a tropical rainforest (pictured in a(ii), licensed under CC BY-SA) has high spatial variability in vegetation (canopy height, land cover) and greater temporal uncertainty in resources, and these non-uniformities create opportunities for higher biodiversity. (b) Individual heterogeneity, defined as differences in phenotype, interest or social interactions/roles. For example, primate troops (baboons, pictured in b(ii), licensed under CC BY) have high phenotypic variation (e.g. different ages, sexes and female reproductive states) [16] and these differences cause conflicts of interest [17,18], heterogeneous interaction networks and specific social roles (e.g. dominance ranks, leader–follower dynamics) [19,20], resulting in high individual heterogeneity. Ungulate herds (goats, pictured in b(i), licensed under CC BY) represent social systems with lower individual heterogeneity because while sexual dimorphism can result in conflicts of interest [21,22], phenotypic variation tends to be lower [23], and so individuals have more shared interests, more homogeneous interaction networks and weaker social hierarchies. (c) Group decision-making requires that individuals use social information and reach a consensus on the timing and nature of their activities [–26]. In cases where individual heterogeneity and ecological heterogeneity are positively correlated (green: both low, purple: both high) [27], we expect that this synergy should select for different decision-making mechanisms with regard to how groups convey (y-axis) and integrate (x-axis) information when reaching consensus. We propose that simple copying of inadvertent cues (e.g. neighbour motion) can underlie group decisions in contexts associated with low heterogeneity (e.g. goat travel directions) [28], while complex signals and integration mechanisms (e.g. vocalizations and quorums) can underlie the negotiation of group outcomes in high heterogeneity contexts (e.g. African wild dog decisions to begin hunting) [29]. In cases where individual heterogeneity and ecological heterogeneity are not positively correlated (e.g. when individual heterogeneity is high but ecological heterogeneity is low), we expect to find group decision-making mechanisms of intermediate complexity.