A Tanganyikan cichlid Neolamprologus mustax selectively exploits territories of another cichlid Variabilichromis moorii due to its inter-individual variation in aggression

Abstract

Animals in a population consistently differ from one another in behavioural types over time and this difference can affect intra- and interspecific relationships. However, empirical studies about roles of behavioural individual variation in interspecific interactions are scarce. Here, we provide evidence that inter-individual variation of a cichlid in aggression affects access to its territory by a heterospecific cichlid. In Lake Tanganyika, a zoobenthivorous cichlid Neolamprologus mustax (Nm) is admitted into territories of an algivorous Variabilichromis moorii (Vm) to prey on benthic invertebrates, while other zoobenthivorous fishes are chased from the territories. We conducted an experiment in which caged Nm fish were exposed twice to each Vm fish in natural habitats. Results indicated repeatable individual variations in Vm aggression towards Nm. Moreover, diving observations indicated that Nm fish frequently used some of Vm territories inside their own territories, but rarely or never used others. This uneven use of Vm territories by the Nm fish was negatively correlated with individual variations in Vm aggression. We conclude that the preferential access of Nm to Vm territory is gained by Nm’s recognising more tolerant Vm fish or discriminating among sites for their territories.