Diet, habitat and ecomorphology of cichlids in the Upper Bladen River, Belize

Abstract

Cichlids are among the most species rich and ecologically diverse families of freshwater fishes. Life history attributes vary greatly among cichlids across their global range, and in the Neotropics alone studies have revealed a great deal of diversity in cichlid ecology, morphology and behavior. This study investigated the habitat use, diet, and ecomorphology of an assemblage of cichlids in the Upper Bladen River, Belize. Mesohabitats, including riffles, runs, deep pools, vegetated areas and adjacent streams, were surveyed and snorkeled, and physicochemical and habitat variables were measured at each site where cichlids were observed or collected. Between 12 and 65 stomachs of each cichlid species were analyzed for diet composition. In addition, traditional morphometrics were completed on five individuals of each species in order to investigate the relationships between morphology, diet, and habitat use. The present study revealed patterns of trophic and morphological diversity consistent with a hypothesis of resource partitioning in accordance with adaptive divergence in morphological traits that influence ecological performance. The Bladen cichlid assemblage has one algivore with a long, coiled gut (Archocentrus spilurus), one piscivore with an elongated body and highly protrusbile jaws (Petenia splendida), two substrate sifters that feed extensively on benthic invertebrates (Astatheros robertsoni and Thorichthys meeki), one midwater invertebrate feeder ('Cichlasoma' salvini), and one large-bodied, trophic generalist (Vieja maculicauda). Species in this assemblage display divergent ecological patterns supported by morphological and behavioral adaptations that yield a degree of diet and habitat segregation. The present study provides not only basic ecological data essential for effective conservation, but also evidence of niche diversification within a local assemblage of heroine cichlids that will be useful for ecological and evolutionary analyses at larger scales of taxonomy, geography, and time.