Assessment strategy and the evolution of fighting behaviour.

The view is examined that the adaptive value of conventional aspects of fighting behaviour is for assessment of relat~ve KMP (resource holding oower) of the combatants. Outcomes o t aggressive disputes should be decided by each individual's fitness budget avaiiltble for expenditure during a fight (determined by the fitness difference between adoption of alternative strategies, escalation or withdrawal without escalation) and on the rate of expenditure of the fitness budget if escalatil-11 occurs (determined by the RHPs of the combatants). Thus response thresholds for alternative strategies ("assessments") will be determined by n,:tural selection on a basis of which ouDonent is likelv to exuend its fitnes budget first. should escalation occur: his "loser" ;hould ietreat (befor. escalation) and the winner should stay in possession of the resour: J. Many aggressive decisions depend on whether one is a resource hc ier, o r an attacker. Assuming thk R H P of the combatants to be equal, thi care many instances of fitness pay-off imbalances between holder and ai:acker which should weight the d i s ~ u t e outcome in favour of one or other oowonent bv allowing it a greater expendable fitness budget. I ually thk*weighting favours the holder; the attacker therefore needs a c~~rrespondingly higher RHP before it may be expected to win. This is not inxxiably the case, and much observed data fits the predictions of this sor. of model. If assessments are perfect and budget expenditure rates exactly predictable, then there would never seem to be any case for escaiatlon. Lscalatlon can be explained In terms ot injury ~nfl~ctlons (expenditures) occurring as discrete events; i.e. as "bouts" won or lost during fighting. As5essrncnt can give only a probabilistic prediction of the outcome of a bout. A simple model is developed to investigate e\calation situations. Each combatant I assesses relat~ve 1 of winning the next bou't '(c,,,). The stake played for is infliciion of loss of I RHP and is determined by the fitness budgets of the opponents. (Each individual plays for the withdrawal of its opponei-it.) This defines a critical probability of winning