VARIATION IN MALE MATING SUCCESS ON LEKS

Studies of variation in male mating success within populations have be en instrumental in shaping perspectives of the role of female choice i n sexual selection. We present simple models to quantify the potential contributions to such variation from a variety of processes: average male mating success (equivalent to the number of female matings per ma le), variation in male and territory quality, male attendance times at leks, and degree of female synchrony, aggregation, and copying. If ma tings occur by chance, we expect variance in male mating success to in crease proportionately with mean mating success. Increasing average ma ting success results in a superproportionate increase in variance when males or their territories differ in quality, when males differ in ti me spent at the lek, when females copy each other, or when females agg regate and mate as a group. In contrast, when females arrive in synchr ony there is a subproportionate increase in variance with respect to m ean male mating success. A review of 36 field studies from 20 species indicates that all studied leks exhibit greater variance in male matin g success than expected by chance. Furthermore, the slope of a regress ion between variance and mean success is significantly greater than un ity, as predicted by the models of variation in male quality, attendan ce at leks, female aggregation, and female copying. In studies of four leks in which we were able to partition the component of variance att ributable to differences among males in attendance at leks, approximat ely 60% of the variance remained unexplained and was attributable to f emale copying, aggregation, or variation in male quality. The framewor k presented here allows a quantified breakdown of variation among male s in mating success and facilitates comparisons among studies of the p otential for sexual selection.