Status signaling games in animal contests

Resource holding potential, subjective resource value, and game theoretical models of aggressiveness signalling

Empirical evidence suggests that aggressiveness (willingness to enter into, or escalate an aggressive interaction) may be more important than the ability to win fights in some species. Both empirical and theoretical traditions treat aggressiveness as a distinct property from the ability (RHP) or motivation (subjective resource value) to win a fight. I examine how these three traits are clearly distinct when modelled using a simple strategic model of escalation. I then examine game theoretical models of agonistic communication and demonstrate that models in which aggressiveness is signalled require: (1) a trait, aggressiveness, which is neither a correlate, nor consequence of RHP or motivation, (2) a handicap which negates any benefit to be gained through the use of a particular signal, and (3) the absence of any other asymmetry which could be used to assign roles to players. I conclude that it is unlikely that these assumptions are ever met, and that empirical examples of "aggressiveness" are far more likely to represent long-term differences in subjective resource value.

When should signals of submission be given?-A game theory model

During contests, losing animals often show signals communicating submission. From an evolutionary viewpoint, however, it is not so obvious why the losing individual gives such a signal instead of running away and why the winning individual accepts the signal instead of inflicting more severe damage. We investigated factors influencing the evolution of signals of submission using a numerical ESS model. The present analysis reveals that there is much space for the evolution of signals of submission, even when the winner of an escalated contest gets some extra benefit. In most cases, signals of submission are given by animals which are slightly or moderately weaker than the opponent. Signals of submission are expected to occur frequently (1) when the value of contested resource does not differ greatly from the cost of injury, (2) when the extra benefit of winning an escalated contest is small, (3) when the opportunity for safe retreat by the losing animal is small, and (4) when the estimation of the difference in the resource holding potential (RHP) between the combatants is accurate but not perfect.

Threat display in birds

The study of threat displays has long been an area in which theory and empirical work have each spurred the other forward. Communication is currently the focus of great interest and effort on the part of modellers. A great deal that classical ethologists have accurately described about threat displays still lacks adequate explanation. Here we review the empirical literature on the use of threat displays by birds competing for small valued resources, both to refocus theoretical attention upon the key characteristics of threat and to assess the degree to which current theory explains these characteristics. We aim to demonstrate that threat displays communicate information about aggressive motivation, but are not handicaps. Handicap models predict a single graded display, while the vast majority of studies report repertoires of about four to six discrete threats for any given species. These displays vary with motivational and strategic considerations, and may be demonstrated to rank consistently on a scale of willingness to escalate, thus providing information about aggressive motivation. We conclude by identifying those features of avian threat displays that have not been adequately explained, in the hope that this reexamination of empirical data will help focus theoretical attention on these issues.