First- and second-order sociality determine survival and reproduction in cooperative cichlids

Cooperative breeders are model organisms for the study of cooperation. The costs and benefits involved in cooperation are typically scrutinised only at the group level. However, multi-level social organisations, involving interactions among individuals at various levels, are often observed. To understand the adaptive value of cooperation and the evolution of complex social organisation, the importance of different levels of social organisation for direct and indirect fitness components should be identified. Here we show that in the cooperatively breeding, colonial cichlid fish Neolamprologus pulcher, both large group size and high colony density significantly raise group persistence and productivity. On the individual level, however, survival is not significantly affected by group size or local density. Yet, breeders in large groups benefit from lower population density by an increased reproductive rate, while breeders in smaller groups have greater reproduction in denser areas. Indirec...