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Behavioral Ecology Vol. 13 No. 3: 337-343
© 2002 International Society for Behavioral Ecology
Protandry models and their application to salmon
Behavioural Ecology Research Group, Department of Biological Sciences, Simon Fraser University, Burnaby BC V5A 1S6, Canada
Address correspondence to Y.E. Morbey, who is now at the Department of Zoology, Ramsay Wright Zoological Laboratories, University of Toronto, 25 Harbord Street, Toronto, ON M5S 3G5, Canada. E-mail: morbey{at}zoo.utoronto.ca .
Mating systems characterized by restricted breeding seasons, male polygamy, and female monogamy are common among animals. In such systems (e.g., butterflies), the earlier emergence of males than females to breeding areas (protandry) is a typical phenological pattern. Protandry likely results from a timing strategy that maximizes mating opportunities by males. In Pacific salmon (Oncorhynchus spp.), males typically arrive at the spawning grounds in advance of females. Using arrival-timing models, I found that under the mate-opportunity hypothesis, the mating system of salmon favors protandry. Protandry is predicted under a range of competitive scenarios, and the degree of protandry is especially sensitive to the duration of male spawning activity. Greater protandry is expected with increasing population sex ratio (i.e., more males) when there is mate guarding, but lower protandry is expected with increasing population sex ratio when interference competition among males reduces male longevity. The timing of unequal competitors is expected to be similar, but among years, protandry may be less variable in the better competitor.
Key words: arrival timing, Onchorhynchus, protandry, salmon.