Reproductive skew and the threat of eviction: a new perspective

Most recent models of the partitioning of reproduction attempt to explain p atterns of skew on the assumption that dominant individuals have complete c ontrol over breeding opportunities within the group, but may nevertheless c oncede a share of direct reproduction to subordinates as an incentive to re main peacefully in the association. Although these models may be applicable to some animal societies, we argue that they fail to provide a comprehensi ve theory of skew Instead, we suggest that subordinates may often be able t o claim unsanctioned reproduction for themselves, but will be forced to exe rcise a degree of reproductive restraint lest they incite ejection by the d ominant. Reproductive skew, in other words, may reflect the threat of eject ion (inducing subordinate restraint) rather than the threat of subordinate departure (inducing reproductive concessions by dominants). We present a si mple evolutionarily stable strategy model of reproductive skew under these circumstances, which demonstrates that a shift in emphasis from reproductiv e concessions by dominants to reproductive restraint on the part of subordi nates, radically alters the predictions of skew models. High group producti vity, high relatedness and (when group members are related) strong ecologic al constraints are all expected to lead to reduced skew (the opposite concl usions to those of previous, concession-based analyses). The reason is that these factors reduce the benefits (or increase the costs) of ejection to t he dominant, who therefore does best to tolerate more subordinate reproduct ion.