Bystander effects and the structure of dominance hierarchies

Prior modeling work has found that pure winner and loser effects (i.e., cha nging the estimation of your own fighting ability as a function of direct p rior experience) can have important consequences for hierarchy formation. W ere these models are extended to incorporate "bystander effects." When byst ander effects are in operation, observers (i.e., bystanders) of aggressive interactions change their assessment of the protagonists' fighting abilitie s (depending on who wins and who loses). Computer simulations demonstrate t hat when bystander winner effects alone are at play, groups have a clear om ega (bottom-ranking individual), while the relative position of other group members remains difficult to determine. When only bystander loser effects are in operation, wins and losses are randomly distributed throughout a gro up (i.e., no discernible hierarchy). When pure and bystander winner effects are jointly in place, a Linear hierarchy, in which all positions (i.e., al pha to delta when N = 4) are clearly defined, emerges. Joint pure and bysta nder loser effects produce the same result. In principle one could test the predictions from the models developed here in a straightforward comparativ e study. Hopefully, the results of this model will spur on such studies in the future.