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Operational sex ratio

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In the evolutionary biology of sexual reproduction, the operational sex ratio (OSR) is the ratio of sexually competing male to females that are ready to mate.[1] It is different from the physical sex ratio in that physical sex ratio also takes into account sexually inactive individual organisms, and sexually non-competitive individuals. This concept is especially useful in the study of sexual selection since it is a measure of how intense sexual competition is in a species, and also in the study of the relationship of sexual selection to sexual dimorphism.[2]


  1. Kvarnemo, C., Ahnesjo, I. (1996). The dynamics of operational sex ratios and competition for mates. Trends in Ecology & Evolution 11 (10): 404–408.
  2. Mitani, J.C., Gros-louis, J.; Richards, A.F. (1996). Sexual Dimorphism, the Operational Sex Ratio, and the Intensity of Male Competition in Polygynous Primates. The American Naturalist 147 (6): 966–980.
  • Tim Clutton-Brock, Science, 318, p. 1882, 21 Dec 2007
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