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

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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
~3>m-e70>Z70mOC70r-ernTABLE 1Empirical data on the relationship between subjective resource value and fighting behaviourEffect of subjective resource value ontSpeciesA hermit crabA spider crabA cray fishFunnel webspiderBowl and doilyspiderA digger waspDung flyDung flyRed-spottednewtIguanaFulmarBald eagleGrey-breastedsilver eyeStarlingStarlingWhite ratRed deerRed deerCommon shrewHouse catChimpanzeeFight Offensive ProbabilityResources Variable duration behaviour of victory Referencefood time of + Hazlett, 1966deprivationfood time of + Hazlett & Estabrook, 1974deprivationfood time of + + Hazlett et al., 1975deprivationweb quality of + + owner+ Riechert, 1979, 1984web sitefemale copulation time + owner+ Austad, 1983nesting no. of katydids + + Dawkins & Brockman, 1980burrow provisionedfemale copulation time + owner+ Sigurjonsdottir & Parker, 1981female female size + owner- Sigurjonsdottir & Parker, 1981(fecundity)female female size + Verrell, 1986(fecundity)nesting depth of + owner+ Rand & Rand, 1976burrow burrowfood time feeding + + Enquist et al., 1985food time feeding + + Hansen, 1986food time feeding + Kikkava, 1968food no. of nestlings + Kacelnik, pets. com.food expected delivery + + Kacelnik, pets. com.from a feederfood time of food + Bruce, 1941deprivationharem size of harem + Clutton-Brock et al., 1979harem receptivity of + Ctutton-Brock et al., 1979femalesfeeding expected food + Barnard & Brown, 1984site availabilityfood time of food + Cole & Shatter, 1966deprivationfood time of food + Nowlis, 1941deprivationt Increase: +, decrease: -.
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