The ecology and ecomorphology of fish assemblages of the Parana-Paraguay River basin in Brazil

The high diversity of freshwater fish found in the Neotropics is paralleled by a remarkable diversity in body shapes. Morphological diversity indicates adaptations to a large variety of habitats and to biological interactions with other fishes leading to niche diversification. The purpose of my dissertation is to investigate the application of the ecomorphological approach in studies of fish assemblage structure in Neotropical freshwater fish communities.; The study area is located in central-southeastern Brazil, and the study sites are located in the High Paraguay and in the Upper Parand. Different aspects of ecomorphological analysis of fish assemblages were considered. First, I examined if ecomorphological attributes correlate with fish diets and habitat utilization, the degree to which ecomorphology predicts functional feeding groups and the vertical distribution of fish, and relationships between ecomorphological and phylogenic patterns. The first two questions were examined using multivariate discriminant and correlation analyses, whereas the third was approached using statistical randomization techniques. The results revealed that arrays of fish morphological measurements were closely correlated with categories of fish diet and habitat utilization, the ecomorphological approach was able to predict both vertical habitat and diet functional groups of these freshwater fish assemblages, and significant correlations between ecomorphological and phylogenetic distances were only observed when matrices with a large number of ecomorphological variables were used.; Then, I investigated whether a metric derived from the ecomorphological approach could be used to describe changes in fish communities. I used community metrics, such as species richness and evenness, and relative and absolute abundance of individual taxa from different sites and times and compared them in an ecomorphological metric. The analysis revealed that the community metrics derived from the ecomorphological approach did not produce clear changes in fish community structure across time and space, but it was able to distinguish between sites under different levels of environmental stress. Inspections of the scatter plots suggested that regions under low environmental stress, represented here by the river sites, were characterized by high fish diversity and diverse trophic guilds, whereas catchments under moderate stress were dominated by only a few species in one or two trophic guilds.