Abstract
In group-living animals, such as primates, the average spatial group structure often reflects the dominance hierarchy, with central dominants and peripheral subordinates. This central-peripheral group structure can arise by self-organization as a result of subordinates fleeing from dominants after losing a fight. However, in real primates, subordinates often avoid interactions with potentially aggressive group members, thereby preventing aggression and subsequent fleeing. Using agent-based modeling, we investigated which spatial and encounter structures emerge when subordinates also avoid known potential aggressors at a distance as compared with the model which only included fleeing after losing a fight (fleeing model). A central-peripheral group structure emerged in most conditions. When avoidance was employed at small or intermediate distances, centrality of dominants emerged similar to the fleeing model, but in a more pronounced way. This result was also found when fleeing after a fight was made independent of dominance rank, i.e. occurred randomly. Employing avoidance at larger distances yielded more spread out groups. This provides a possible explanation of larger group spread in more aggressive species. With avoidance at very large distances, spatially and socially distinct subgroups emerged. We also investigated how encounters were distributed amongst group members. In the fleeing model all individuals encountered all group members equally often, whereas in the avoidance model encounters occurred mostly among similar-ranking individuals. Finally, we also identified a very general and simple mechanism causing a central-peripheral group structure: when individuals merely differed in velocity, faster individuals automatically ended up at the periphery. In summary, a central-peripheral group pattern can easily emerge from individual variation in different movement properties in general, such as fleeing, avoidance or velocity. Moreover, avoidance behavior also affects the encounter structure and can lead to subgroup formation.
Highlights
Understanding animal behavior within its social context remains a challenge, since individuals are situated in a complex social environment that consists of many interacting entities and is typically structured, both spatially and socially [1,2,3,4]
A particular socio-spatial structure often reported in primate studies is a central-peripheral group pattern, i.e. dominant individuals are at the center of the group and subordinates populate the periphery
By means of an agent-based model called DomWorld, Hemelrijk showed that aggressive dominance interactions and subsequent fleeing by the loser gives rise to a central-peripheral spatial structure [5]
Summary
Understanding animal behavior within its social context remains a challenge, since individuals are situated in a complex social environment that consists of many interacting entities and is typically structured, both spatially and socially [1,2,3,4]. A particular socio-spatial structure often reported in primate studies is a central-peripheral group pattern, i.e. dominant individuals are at the center of the group and subordinates populate the periphery (macaques: [7,8,9,10,11,12,13,14,15,16], capuchins: [17,18,19], baboons: [20,21,22]). By means of an agent-based model called DomWorld, Hemelrijk showed that aggressive dominance interactions and subsequent fleeing by the loser gives rise to a central-peripheral spatial structure [5] This spatial pattern emerged through self-organization, meaning that the model individuals had no preference for any spatial location whatsoever. Such a cognitively minimalistic proximate mechanism is likely to extend far beyond the primates
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