We present a theoretical investigation of the dependence of divorce rate on longevity, variation in quality between mates, and the cost of divorce or mate retention. We model the decision of a female on whether to divorce her mate after breeding. This decision is based on his quality. We shown that it is optimal for the female to divorce if the reproductive success in breeding with the mate next year is less than the average annual future success if she divorces. Under this strategy the female's mean annual divorce rate declines with age, while her mean annual reproduction success rises. We investigated the annual divorce rate, averaged over the lifetime of the female. Costs caused this divorce rate to increase with variance of male quality. When divorce resulted in a loss in reproductive success in the following year, this divorce cost reduced divorce in short-lived species far more than in long-lived species. The reverse was true for mortality costs. A mate retention cost of overwinter mate death increased divorce in short-lived species dramatically, while long-lived species were little affected. Female choosiness increased with longevity, but this did not necessarily increase divorce rates averaged over the female's life. The selection pressure agains the suboptimal strategies of obligate divorce and obligate mate retention increased strongly with longevity.
Appeared as McNamara, J.M. and Forslund, P. (1996). "Divorce rates in birds: prediction from an optimization model". American Naturalist, 147 pp 609-640.
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John McNamara |
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