ECOMORPHOLOGICAL DIVERSIFICATION AND CONVERGENCE IN FLUVIAL CICHLID FISHES

We compared ecological and morphological patterns among cichlid faunas from three different biotic regions: the Rio Tortuguero/Rio Sarapiqui in Costa Pica, the Rio Apure drainage in Venezuela, and the Upper Zam bezi drainage in Zambia. Cichlids comprise 19 percent of the fish faun a in the Tortuguero and Upper Zambezi drainages and 6.5 percent in the Apure drainage. Cichlid faunas exhibited similar patterns of habitat and food resource utilization, although vegetation-dwelling is more co mmon and detritivory and herbivory are rarer in the Apure fauna. We hy pothesize that South American ostariophysan fishes were more preadapte d than cichlids to exploit detritivore and herbivore niches. The Zambe zi cichlid fauna shows less ecomorphological diversification than the other two faunas, even though the degree of dietary diversification is similar among faunas. Chaetobranchus flavescens from the Venezuelan f auna is the only species that specializes on zooplankton as an adult, and algae grazing (Neetroplus nematopus) and specialized fruit feeding ('Cichlasoma' tuba) were represented only in the Costa Rican fauna. B ased on the most recent hypothesized phylogeny for the family Cichlida e, we identified numerous interfaunal ecomorphological and feeding nic he convergences. Patterns of ecomorphological divergence in relation t o cladogenesis indicate a faster rate of evolutionary niche diversific ation in Central American cichlids compared with the two other faunas.