Using potential reproductive rates to predict mating competition among individuals qualified to mate

The potential reproductive rate (PRR), which is the offspringproduction per unit time each sex would achieve if unconstrainedby mate availability, often differs between the sexes. An increasingsexual difference in PRR predicts an intensified mating competitionamong the sex with the higher PRR. The use of PRR can providedetailed predictions of when, where, and how the intensityin mating competition and hence sexual selection will vary.Previous models have focused on the "time out" from mate searchingas a major component of PRR. Here, we suggest some improvementsand clarifications: in a population where individuals haveto compete for specific resources that are prerequisites formating (e.g., nest sites), individuals unable to obtain sucha resource will not qualify to mate. We suggest how a conceptof the ratio of males and females qualified to mate, Q, canimprove previous models designed to use the sexual differencein PRR to estimate the operational sex ratio (OSR). Further,when estimating the sexual difference in PRR of a population,it is important that each sex is given free access to matingpartners. Jointly, this provides an empirical approach basedon estimates of Q and the sexual difference in PRR.