Dynamics of Hierarchy Formation: the Sequential Development of Dominance Relationships

Abstract

A method for investigating the behavioral sequences used in forming dominance hierarchies is presented. There are four possible sequences for the formation of the first two dominance relationships in groups of three individuals (triads). Designating the winner in the first relationship formed as the initial dominant, the loser as the initial subordinate, and the animal not involved as the bystander, the four possible sequences are: (1) the initial dominants goes on to dominate the bystander (Double Dominance), (2) the bystander later dominates the initial subordinate (Double Subordinance), (3) the bystander later dominates the initial dominant (Bystander Dominates Initial Dominant), and (4) the initial subordinate later dominates the bystander (Initial Subordinate Dominates Bystander). Although each sequence has an equal probability of occurrence if dominance relationships are formed randomly, two of the sequences have different implications for the formation of the empirically common linear and near linear hierarchies than the other two. Linear and near linear hierarchies are, by definition, composed of all or nearly all triads with transitive dominance relationships (A dominates B, B dominates C, and A dominates C), while hierarchies far from linearity have many triads with intransitive relationships (A dominates B, B dominates C, and C dominates A). Double Dominance and Double Subordinance sequences guarantee the formation of triads with transitive dominance relationships, but the other two sequences can give triads with either transitive or intransitive relationships. Linear and near lincar hierarchies are ensured, therefore, by a preponderance of Double Dominance and Double Subordinance sequences in the component triads of larger groups. In an application of the method developed, sequences of dominance relationships formed in groups of three and four chickens were analyzed. In both experiments Double Dominance and Double Subordinance composed the overwhelming majority of all sequences - 91 % in triads and 87 % in tetrads. A further set of results indicated that intransitive relationships were common in constructed triads where chickens met only as component pairs and not in real triads where all three met together at the same time. These results suggest that hierarchy formation can be best viewed as a developmental process where preceding dominance interactions influence succeeding ones. This view was characterized as the jigsaw puzzle model of hierarchy formation, and it was contrasted with the more classical approach of explaining hierarchy structures by differences in the individual characteristics of group members. Many species beside chickens form linear and near linear hierarchies, and it was hypothesized that Double Dominance and Double Subordinance sequences also compose the majority of sequence occurrences in many of these species. The data available for other species were reviewed and offered tentative support for the hypothesis.