Summary

Reproductive skew models provide a powerful theoretical tool for understanding the way reproduction is shared in animal societies. However, testing skew models empirically has proved problematic, partly due to the difficulties of ensuring that all the assumptions of the model have been met, and partly because the parameters to be tested often correlate with other factors likely to influence skew.

Two broad sets of processes are likely to act in tandem to influence reproductive skew in societies where dominants and subordinates are equally capable of breeding successfully. First, reproductive skew is likely to be influenced by the extent to which subordinate reproduction is costly to dominant females, as dominants would only be expected to disrupt subordinate breeding attempts if they benefit from doing so. Second, reproductive skew is likely to be influenced by the extent to which dominants are able to disrupt subordinate breeding attempts.

Before testing the predictions of competing skew models, empirical work should investigate the underlying causes of variation in reproductive skew in the species in question. This will involve a detailed investigation of (1) the factors that influence female breeding success that are not a consequence of interference from other parties (such as age, condition, access to unrelated breeding partners); (2) the costs and benefits that dominant and subordinate individuals experience when breeding together; and (3) the tactics that competing parties use to maximize their own breeding success. This should yield insights into the extent to which the observed level of skew is optimal for either competing party, which would provide better knowledge of which party is in control of reproduction and which skew models are applicable.