Evolution of Fighting Behaviour: The Effect of Variation in Resource ...

198M. ENQUIST AND O. LEIMARII10/~5~ZC t I0-5 1 1.5Resource volueFIG. 6. Expected fight duration as a function of resource value for the ESS for the owner-intrudergame with an information asymmetry shown in Fig. 3. Curve 1 refers to fights won by the intruder, curve2 to all fights, and curve 3 to fights won by the owner.be 1.0 both for owners and intruders) we obtain a situation with an uncorrelatedrole asymmetry. Intuitively, it would seem that such a situation is less asymmetricand more favourable to intruders than when owners are more informed about theresource. However, comparing the owner's probability of winning and overall utilitybetween the information asymmetric case studied here and the situation with anuncorrelated role asymmetry studied in Leimar & Enquist (1984), one obtains thatthe owner has a higher probability winning and a higher utility with the ESS forthe uncorrelated role asymmetry. This indicates that information asymmetry per sehas a rather small importance when it comes to explaining why in nature ownerstend to win most owner-intruder interactions. It also shows that intuition cansometimes be a poor guide to the solution of game theory problems.Comparison With Empirical DataEffects of resource value on contest behaviour have been demonstrated in severalstudies, and we now discuss to what extent results from such studies are in agreementwith predictions from game theory. The behavioural parameters usually analysedin relation to variation in resource value are fight duration, frequencies of variousbehaviour patterns, and, in asymmetrical situations probability of victory. The datawe have found in the literature on relationships between these variables and resourcevalue are summarized in Table 1.In those studies where they have been analysed, both fight duration and thefrequency of potentially dangerous behaviour patterns (offensive behaviour in Table1) increase when resource value increases. The cost of fighting has been measureddirectly in a study of male bowl and doily spiders competing for females (Austad,1983). The cost was estimated as the relative frequency of fatal injuries, and wasshown to increase with the value of the female. The results on fight duration anduse of offensive behaviour patterns in Table 1 also suggest that the cost of fighting