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

The potential reproductive rate (PRR), which is the offspring production per unit time each sex would achieve if unconstrained by mate availability, often differs between the sexes. An increasing sexual difference in PRR predicts an intensified mating competition among the sex with the higher PRR. The use of PRR can provide detailed predictions of when, where, and how the intensity in mating competition and hence sexual selection will vary. Previous models have focused on the ‘‘time out’’ from mate searching as a major component of PRR. Here, we suggest some improvements and clarifications: in a population where individuals have to compete for specific resources that are prerequisites for mating (e.g., nest sites), individuals unable to obtain such a resource will not qualify to mate. We suggest how a concept of the ratio of males and females qualified to mate, Q, can improve previous models designed to use the sexual difference in 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 mating partners. Jointly, this provides an empirical approach based on estimates of Q and the sexual difference in PRR. Key words: mating competition, operational sex ratio, OSR, adult sex ratio, potential reproductive rate, PRR, qualified to mate, resource competition. [Behav Ecol 12:397–401 (2001)]