| Summary: | The wide diversity of Patagonian freshwater ecosystems may be classified into three groups: glacial Andean lakes, Extra-andine closed depressions, and rivers and man-made lakes. We here analysed the biotic structure of Patagonian lentic and lotic ecosystems. We focus on the effect of both abiotic (climate, water composition, etc.) and biotic factors (competition, predation) on species diversity and composition of these communities. Zooplankton (rotifers and copepods) and macrobenthic insects (Plecoptera) were chosen as examples of the distribution patterns observed in lakes and rivers respectively. Rotifer species richness was explained by altitude, while species composition was related with conductivity. Three different rotifer assemblages were identified and associated with particular ranges of conductivity. In addition, the distribution of two rotifer genera, Keratella and Asplanchna, was related with biotic interactions (competition and predation). Crustacean size spectrum depended on visual fish predation. Plecoptera species richness decreased as a function of the stream order. Low stream order covered by Nothofagus forest showed the highest species number.
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