Data from: Group-size dependent punishment of idle subordinates in a cooperative breeder where helpers pay to stay

In cooperative breeding systems, dominant breeders sometimes tolerate unrelated individuals even if they inflict costs on the dominants. According to the ˈpay-to-stayˈ hypothesis, (i) subordinates can outweigh these costs by providing help and (ii) dominants should be able to enforce help by punishing subordinates that provide insufficient help. This requires that dominants can monitor helping and can recognize group members individually. We tested whether in a pay-to-stay system dominants are constrained in their ability to monitor and punish subordinates. In a field experiment we prevented subordinates from helping in large and small groups of the cooperatively breeding cichlid Neolamprologus pulcher. After resuming their duties these subordinates received more aggression and increased submissiveness than did control individuals, suggesting that punishment occurred to enforce help. Subordinates in small groups increased their help more than those in large groups, despite receiving less aggression. When subordinates were temporarily removed, dominants in small groups were more likely to evict returning subordinates. Our results suggest that only in small groups helpers face a latent threat of punishment by breeders as predicted by the pay-to-stay hypothesis. In large groups cognitive constraints may prevent breeders to track the behaviour of a large number of helpers.