Male Dominance and Copulation Disruption Do Not Explain Variance in Male Mating Success On Sharp-Tailed Grouse (Tympanuchus Phasianellus) Leks

Abstract

This study tested two hypotheses: that male-male competition and dominance relationships among males, rather than female choice of mates, principally determined the extreme variance in male mating success at sharp-tailed grouse leks; and, that male-male competition and dominance relationships among males principally determined the structure of the lek mating system as suggested by the recent model of lek organization (BEEHLER & FOSTER, 1988). Not all males in the study population obtained lek territories and more of those males that did were adults and had longer tarsometatarses than non-lekking males, which only visited leks and displayed elsewhere. There were no differeces between lekking and non-lekking males in mean body mass, wing length, and supraorbital comb size however. Dominant males, where dominance was measured by differences in the frequency that males were disrupted during courtship of females by neighbours, were not the most successful at obtaining copulations at leks. This is the strongest evidence that we have against the complete applicability of the hotshot model to our population of sharp-tailed grouse. Dominance status could not be predicted on the basis of body size, comb size, or age class. Dominant males were not the owners of the most centrally-located territories, nor were the territories of the most successful males at obtaining copulations taken over by more dominant males after successful males were removed from their territories. These results too provide evidence against the applicability of the hotshot model to our population of sharp-tailed grouse. Copulation disruptions by neighbouring males were common at leks. Copulations were more likely to be unsuccessful when they were disrupted than otherwise and remating by individual females occurred more often after they were disrupted than otherwise. However, based on limited sample sizes, females were apparently no more likely to remate with the disrupting male than with any other and copulation disruptions only redistributed copulations among an already successful number of males. Only 26% of the variance in male mating success could be explained in a multiple regression by any two- or three-variable combination of male traits and this was explained by variance in male size and number of yellow leg-bands. Male mating success and male size were inversely correlated in individual tests of significance; on average, smaller males apparently obtained more matings. The more centrally-located males apparently obtained more matings, but territory location was not correlated with any other variable except (perhaps) survival. There was a tendency for surviving males to change from more exterior to more interior locations in successive years, apparently as a result of new males settling around them rather than as a result of direct competition for interior spots. Male removal experiments were performed in which the most successful males were removed on each of number of leks. Contrary to predictions of the hotshot model (BEEHLER & FOSTER, 1988), male recruitment to these leks and the numbers of females visiting and mating at these leks the following year did not decline, and there was no increase in the frequency of disrupted copulations in the year following male removal. Consistent with the hotshot model, however, the variance in male success apparently declined at two of three leks in the year following male removal.