Field experiments on species recognition by the threespot damselfish, Eupomacentrus planifrons, (Pisces: Pomacentridae)

Abstract

The threespot damselfish, Eupomacentrus planifrons, defends differently sized territories against individuals of different species. Tests were conducted in the field to determine the mechanism(s) by which this interspecific recognition occurs. It was found to be based largely on visual cues, the most important of which was body form. Both colour and movement had different effects for intra- and inter-specific intruders. Based on these data, it is proposed that different mechanisms underlie the recognition of and territorial defence against the two groups. Further, interspecific territoriality need not be an ‘accidental’ form of intraspecific territoriality nor a transitional phase in the divergence of already established species, but, rather, may be a stable system based on the simple need to defend an area against non-related competitors.