The cost of polygyny - definitions and applications

The polygyny threshold model was introduced in the 1960s in order to explain why females in some species choose to mate vith already mated males. Since then, a number of complementary or alternative hypotheses have been suggested. By using a hierarchical testing approach Searcy and Yasukawa (1989) organised the models that proposed to explain the maintenance of territorial polygyny. Here, I point out that there is no true way to organise the models, and that the organisation itself may influence which explanation the observations mill support. In particular, I discuss Searcy and Yasukawa's distinction between cost and no-cost models. As an alternative to the hierarchical approach I suggest careful comparisons of those variables that inflict costs of sharing with those that provide compensation. While the hierarchical approach may put very similar systems in different model families, a cost and benefit evaluation might instead show that the difference is quantitative rather than qualitative. Also, an identical cost of polygyny can arise from several different combinations of costs of sharing and benefits of sharing. Hence, the hierarchical approach may put systems with different mechanisms behind polygyny into the same model family.