The theory of family-group dynamics predicts that group structure, helping behaviour and social interactions among group members should vary with the opportunities of subordinates to breed independently. We investigated experimentally whether unrelated mature helpers in the cooperatively breeding cichlid Neolamprologus pulcher reduce costly social and cooperative behaviour and choose to disperse and breed independently when offered vacant breeding sites. As predicted by the ecological constraints hypothesis, when breeding substrate was available, (i) helpers spent more time in dispersal areas and it was mainly large helpers that left the group to breed independently; (ii) all helpers invested less in costly submissive behaviours towards other group members and large helpers reduced help, supporting the ‘pay-to-stay’ hypothesis; and (iii) large helpers, particularly those that dispersed and bred, increased more in body mass in the treatment than those without breeding options, suggesting status-dependent strategic growth of helpers. We conclude that helpers of N. pulcher decide whether to stay and pay or disperse and breed in response to constraints on independent breeding.
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