INDIVIDUAL MATING SUCCESS, LEK STABILITY, AND THE NEGLECTED LIMITATIONS OF STATISTICAL POWER

The evolution of leks (aggregations of males displaying to females) ca nnot be explained solely by an increasing average gain in matings for each male as group size increases. This is because the mating skew, th at is, the inequality among males in mating success, is often high and may vary with lek size. Here, we show that the common observation tha t matings become more evenly divided as lek size increases is also ins ufficient to explain by itself the benefits of aggregating. The benefi ts to individual males are highly sensitive to the exact relationship between mating skew and lek size, and very similar relationships can l ead to opposite predictions concerning individual benefits. With data on published mating success for 18 species (71 leks), we show that dif ferent species have very similar skew versus lek size relationships. W ith current sample sizes, however,there is insufficient statistical po wer to distinguish between completely different alternatives concernin g individual optima of males. (C) 1998 The Association for the Study o f Animal Behaviour.