Abstract

Because of the fundamental asymmetry between the sexes, males typically compete for access to females. Hence, most studies on intra-sexual mating aggression have focused only on males, and have shown increasing aggression with increasing operational sex ratio (OSR). However, one study documented a "dome-shaped" relationship between aggression and OSR, presumably because aggression became ineffective at high competitor densities as predicted by resource defence theory. The few studies that have investigated female intra-sexual aggression have used only a narrow range of OSR. The purpose of my study was to investigate the patterns of both male and female mating aggression over a broad range of OSR. I also compared how females competed for two different resources, food and mates. Male and female aggression initially increasing with OSR, peaked and then levelled off. For a given value of OSR, however, the rate of male aggression was higher than female aggression. The rate of male aggression was consistent with a dome-shaped pattern, whereas the rate of female aggression did not decrease at high levels of OSR. In contrast, courtship rates for both males and females decreased with increasing OSR in a linear manner. The pattern of male and female intra-sexual aggression were broadly consistent with the predictions of resource defence theory.