Abstract
Dominance hierarchies are group-level properties that emerge from the aggression of individuals. Although individuals can gain critical benefits from their position in a hierarchy, we do not understand how real-world hierarchies form. Nor do we understand what signals and decision-rules individuals use to construct and maintain hierarchies in the absence of simple cues such as size or spatial location. A study of conflict in two groups of captive monk parakeets (Myiopsitta monachus) found that a transition to large-scale order in aggression occurred in newly-formed groups after one week, with individuals thereafter preferring to direct aggression more frequently against those nearby in rank. We consider two cognitive mechanisms underlying the emergence of this order: inference based on overall levels of aggression, or on subsets of the aggression network. Both mechanisms were predictive of individual decisions to aggress, but observed patterns were better explained by rank inference through subsets of the aggression network. Based on these results, we present a new theory, of a feedback loop between knowledge of rank and consequent behavior. This loop explains the transition to strategic aggression and the formation and persistence of dominance hierarchies in groups capable of both social memory and inference.
Highlights
Individuals from social species must interact with each other to reproduce, find food, and survive
We show that individuals can use localized patterns in the aggression network to learn the relative ranks of individuals, and that these signals of rank strongly correlate with individual decisions to aggress
We find no evidence that rank could be reliably determined based on simple underlying cues such as size or spatial proximity
Summary
Individuals from social species must interact with each other to reproduce, find food, and survive. Higher-level social structures such as hierarchies emerge when interacting individuals need to manage trade-offs in the costs and benefits of social associations [1, 2]. One of the most important is the dominance hierarchy, where group-wide “global” rankings are derived from local aggressive interactions, and form emergent social properties [3,4,5]. Individuals may fight to gain immediate access to contested resources, or they may aggress in order to gain rank, which provides these individuals with delayed rank-dependent benefits. Aggression that results in higher dominance rank often increases an individual’s access to foraging resources and reproductive opportunities Aggression that results in higher dominance rank often increases an individual’s access to foraging resources and reproductive opportunities (e.g., Ref. [6,7,8])
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