Summary: Byers & Dunn (2012)

 Male male competition and female mate choice are two aspects of sexual selection. In the case of male-male competition, the advantage of a competitor is largely determined by his fecundity, that is, the number of offspring he sires. Angus Bateman characterised this interaction in the form of a quantitative relationship known as the Bateman slope. This slope graphically depicts the relationship between a male's number of mates and the number of offspring produced. The potential for sexual selection is estimated from the slope of the line. Male mating success often relies on sexual dimorphism, and males with larger (heavier etc). traits are likely to achieve more matings. Generally, sexual dimorphism requires a positive Bateman slope. However, natural selection and random effects may also influence a male's ability to win mates. Byers & Dunn (2012) found a yearly positive Bateman slope for pronghorn Antilocapra americana over a decade, with no indication that random effects were skewing male mating success. They did find that there was variation between years due to fawn predation. Byers & Dunn (2012) suggest that environmental and/or extrinsic factors could limit sexual selection potential, but in general, the validity of a positive Bateman relationship is supported.