Local-scale habitat influences morphological diversity of species assemblages of cichlid fishes in a tropical floodplain river

We examined the taxonomic and morphological diversity of cichlid fish assemblages in a floodplain river in Venezuela during the dry season at two spatial scales: macrohabitats (lagoons, main channels and creeks) and mesohabitats (leaf litter, sand banks, rocky shoals and woody debris). Nonmetric multidimensional scaling did not reveal differences for species assemblages among macro and mesohabitats. The first two axes from canonical correspondence analysis based on 19 species and six physical variables modelled >61% of the taxonomic variation in assemblages from rock shoals and woody debris, and 55% of variation in assemblages from sand banks and leaf litter. Principal components analysis based on 22 morphological variables yielded two dominant axes that explained >86% of variation in the cichlid assemblages. Morphological diversity was analysed to test the idea that assemblage structure is nonrandom, with structurally complex habitats supporting more species with more functional morphological diversity than simple habitats. Average and standard deviation (SD) of the morphological Euclidean distances of local assemblages among mesohabitats tended to decrease or be constant as the number of species increased. Regressions of the average nearest neighbour distance (NND) and SD of NND with species richness resulted in low and negative slopes of species assemblages among mesohabitats. These relationships suggest that when more species are added to a habitat patch, assemblage morphospace remains approximately constant, species average similarity increases and species dispersion in morphological space becomes more uniform. Results support that cichlids partition habitat at the local scale but not at the macrohabitat scale. C. G. Montaña, K. O. Winemiller Section of Ecology, Evolution and Systematic Biology, Department of Wildlife & Fisheries Sciences, Texas A&M University, College Station,