Abstract
In many groups of animals the dominance hierarchy is linear. What mechanisms underlie this linearity of the dominance hierarchy is under debate. Linearity is often attributed to cognitively sophisticated processes, such as transitive inference and eavesdropping. An alternative explanation is that it develops via the winner-loser effect. This effect implies that after a fight has been decided the winner is more likely to win again, and the loser is more likely to lose again. Although it has been shown that dominance hierarchies may develop via the winner-loser effect, the degree of linearity of such hierarchies is unknown. The aim of the present study is to investigate whether a similar degree of linearity, like in real animals, may emerge as a consequence of the winner-loser effect and the socio-spatial structure of group members. For this purpose, we use the model DomWorld, in which agents group and compete and the outcome of conflicts is self-reinforcing. Here dominance hierarchies are shown to emerge. We analyse the dominance hierarchy, behavioural dynamics and network triad motifs in the model using analytical methods from a previous study on dominance in real hens. We show that when one parameter, representing the intensity of aggression, was set high in the model DomWorld, it reproduced many patterns of hierarchical development typical of groups of hens, such as its high linearity. When omitting from the model the winner-loser effect or spatial location of individuals, this resemblance decreased markedly. We conclude that the combination of the spatial structure and the winner-loser effect provide a plausible alternative for hierarchical linearity to processes that are cognitively more sophisticated. Further research should determine whether the winner-loser effect and spatial structure of group members also explains the characteristics of hierarchical development in other species with a different dominance style than hens.
Highlights
Dominance hierarchies are a near universal pattern of social order in group-living animals [1]
Most promotions in rank came from an agent attacking another that was lower in rank, which increased its dominance score until it surpassed that of an individual ranking above itself
As to the similarity in hierarchy development between groups in DomWorld and real hens [21], we showed that groups in DomWorld developed a highly linear and stable hierarchy with characteristics similar to those of hens (Table 3)
Summary
Dominance hierarchies are a near universal pattern of social order in group-living animals [1]. The prior attributes hypothesis proposes that attributes individuals possess prior to hierarchy formation, such as body size or correlated traits, directly determine their rank position in a linear hierarchy [7]. This theory is supported by empirical data on pair-wise dominance interactions [8], but has been rejected in some theoretical studies because for prior attributes to produce (near) linear hierarchies difficult mathematical conditions would be required, especially in larger groups [9,10,11]. Because the differences in attributes among individuals decrease with group size, Chase and Lindquist [11] argue it is unlikely that differences in prior attributes alone directly produce (near) linear hierarchies
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