The relationship between ecology and the optimal helping strategy in cooperative breeders

Cooperative breeding is a social system in which certain individuals (auxiliaries) postpone or forgo their own reproduction to help other individuals (breeders). The selective advantage for this behaviour has been considerably debated, but that debate has focused on models that neglect long-term evolutionary dynamics. As a result, there is little theoretical understanding of how system ecology relates to either optimal strategies or the scope for breeder-auxiliary conflict. In this paper, we construct an explicit population model of cooperative breeding when help is under either maternal and auxiliary control, and obtain an ecologically-specific optimal strategy. Our optimal strategy reveals that there is a critical point at which helpers are no longer 'making the best of a bad situation', and are instead exploiting the breeders. The critical value at which this occurs delineates two qualitatively different ecological regimes. We also show that ecologies with constraints upon becoming a breeder, or unappealing aspects of being a breeder (e.g. high breeder mortality), minimize breeder-auxiliary conflict, whereas when there are appealing aspects (e.g. low breeder mortality) and few constraints, breeder-auxiliary conflict is maximized.