Аннотация:This chapter deals with the operational sex ratio (OSR) and its importance for understanding mating competition, which is a key component of sexual selection. We focus on OSR as an empirical measurement with important applications in sexual selection, but we also pay considerable attention to the question of how to estimate sexual differences in potential reproductive rates (PRR). The sexual difference in PRR and the adult (or qualified) sex ratio are the most important factors influencing the OSR, and thus the pattern of sexual selection in a population. We illustrate our points using examples from a wide range of taxa. In particular, we investigate how environmental factors, through their effects on PRR and OSR, often add a dynamic to mating competition, which sometimes results in different sex roles and varying intensities being displayed in different populations or at different times within a breeding season. Finally, we consider some examples of contrasting patterns, how OSR relates to mate choice and prospects for further research.
