Dung fly struggles: A test of the war of attrition

Abstract

1. In Maynard Smith's 'war of attrition' model of animal conflict, two identical opponents fight over a unitary resource and the winner is the individual that is prepared to go on longer. The evolutionarily stable strategy (ESS) is for individuals to vary in their selection of 'bids' (fighting durations) so that the probability density of bids follows a negative exponential distribution. In nature, the distribution of selected bids cannot be observed directly, because contests are terminated by the opponent with the lower bid. We therefore derive an expected distribution of contest persistence times. 2. Struggles between male dung flies (Scatophaga stercoraria) for possession of a female can be evaluated in terms of Darwinian fitness as expected number of eggs fertilised/time. Fitness calculations must account for the energetic costs of struggling relative to searching for an alternative female; a plausible range of relative energetic costs is deduced. Though there is a superficial concordance of observed struggle persistence times with that predicted from a war of attrition with linear costs, this breaks down when the data are analysed in component categories. Further, dung fly struggles are clearly asymmetric contests. We suggest that struggles are settled by a form of assessment strategy involving acquisition of information during the contest about the relative resource holding powers of the two contestants. © 1980 Springer-Verlag.