Intra- and interspecific social organization among three herbivorous cichlid fishes in Lake Tanganyika

Intra- and interspecific social organization among 3 coexisting herbivorous cichlids,Tropheus moorii, Petrochromis trewavasae andP. orthognathus, were studied at a rocky shore in Lake Tanganyika. Individuals of all species maintained discrete intra- and interspecific territories, exceptT. moorii andP. trewavasae whose feeding territories overlapped. Territory owners attacked smaller individuals but exhibited displays towards larger neighbours, irrespective of species. This observation suggests that both intra- and interspecifically, these cichlids interact in the context of size-dependent dominance hierarchies. Removal experiments showed that smallerT. moorii benefitted fromP. trewavasae in the maintenance of their territory borders against largerP. orthognathus. Interspecific dominance hierarchy and commensalism among these cichlids are not species specific, but change dynamically in relation to the difference in body size between component individuals. Mating territories of maleP. orthognathus andT. moorii are compared to their feeding territories, and territory forms are discussed. It is suggested that an approach incorporating the concept of an interspecific society may play an important role in the elucidation of guild structure and function.