The ratio between reproductively mature males and females available for mating in a given time is called the 'operational sex ratio'. The operational sex ratio influences the intensity of mating competition. For example, if only a few females are ready to mate while many males are ready, the operational sex ratio is male-biased, and mate competition among the males is strong. Local mate competition among individuals of the same sex can give a rise to sexual selection, in which traits that enhance the attractiveness or competitiveness of the competing mates are favored. This process can result in the evolution of highly conspicuous secondary sexual traits and in sexual dimorphism.
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