Experimental evaluation of the roles of habitat selection and interspecific competition in determining patterns of host use by two anemonefishes

We examined the roles of interspecific competition and habitat preference i n determining the distribution of 2 anemonefish species, Premnas biaculeatu s and Amphiprion melanopus, among the 2 morphs of the anemone Entacmaea qua dricolour. This anemone species has a solitary morph which is usually occup ied by a single pair of P. biaculeatus and a colonial morph which is usuall y occupied by large social groups of A. melanopus. The possibility that int erspecific competition, and/or preference of adults of each species of fish for the anemone morph it usually occupies, determines this distribution wa s tested using aquarium based experiments. Adults of one species, A. melano pus, displayed a preference for the anemone morph it usually occupies in th e field, but P, biaculeatus did not. Instead, P. biaculeatus pairs tended t o associate closely, always occupying the same anemone regardless of the mo rph chosen. While interspecific competition limited fish abundance within a nemones, competitive interactions could not explain the distribution of fis h species among anemone morphs. That is, neither fish species displaced the other more often on the anemone morph it usually occupies in the field. Wh ile juvenile P. biaculeatus exhibit some preference for solitary morphs and A. melanopus appear to prefer colonial morphs, juvenile distributions cann ot fully explain the distribution of adults. Instead, we suggest that adult distributions are explained by a combination of juvenile habitat preferenc es, adult-juvenile interactions and constraints imposed by the contrasting social systems of the 2 species.