Citation: de Jong, K., E. Forsgren, H. Sandvik, and T. Amundsen (2012) Measuring mating competition correctly: available evidence supports operational sex ratio theory. Behavioral Ecology, 23, 1170–1177. doi: 10.1093/beheco/ars094 [what’s a doi?]. Key words: Courtship, frequency measure, OSR, propensity measure, sex role, sexual selection.
Full text: © 2012 The authors. The original publication is available at Oxford Journals. If you accept (i) that further reproduction, and all further use other than for personal research, is subject to permission from the publisher (Oxford University Press), and (ii) that printouts have to be made on recycled paper, you may download the article here (pdf, 18.3 MB). Lay summary: In most sexually reproducing animals, males compete for females. However, it is not always that simple: in some animals, females compete for males or both sexes compete. The classical theory to explain the intensity of mating competition has been that the more abundant a sex is, the more competitive. This is expected simply because the other sex will then become a scarce resource. Surprisingly, this theoretical expectation is often not confirmed by experiments. Mating competition may be expressed through contests within a sex to establish dominance or courtship to convince the other sex of one’s superiority. For courtship behavior, many experimenters find that animals court more when the opposite sex is abundant, which – seemingly – contradicts theory. We argue that this apparent clash between theory and experimental outcomes may be caused by the way behavior is measured in experiments. Often, the number of courtship displays per animal is counted under different sex ratios. We show that one cannot properly test theory this way. The reason is simple: when the other sex is abundant, an animal will more often meet a potential mate and will have more opportunities to court. This can lead to an increase in courtship displays even if the animal is less eager to court. Instead, we need to measure the propensity to court – how likely it is that an animal courts when it meets a potential mate. We show that studies measuring courtship this way support theory: when mates are limited, animals are more eager to court. Supplementary material: An overview of studies reporting the effect of variation in OSR on courtship behavior is available here (as an Excel spreadsheet, 49 kB).
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