Abstract
A study was undertaken to define the benthic populations, the environmental‐ecological variability and trophic aspects according to the functional feeding groups in the upper reaches of the Nera River, a tributary of the Tiber, in central Italy. A total of 12 681 individuals was collected and 83 taxa were identified; 11 proved to be endemic for Italy, 7 of them typical of the central Apennines. The greatest number of taxa (58), and the highest values of diversity were recorded at the lowest sampling station, 37 km from the source. A dendrogram constructed by the UPGMA method based on values of similarity revealed two main clusters, one identified with crenon (at the source) and the other with rhithron (the downstream stations) fluvial typology. Correspondence analysis on the environmental matrix parameters confirmed this finding. Taxa abundance was evaluated by grouping the individuals collected into classes using semi‐quantitative sampling. The results of trophic‐functional analysis, calculated on the basis of the estimated abundance and tested with statistical methods, agreed with fauna composition analysis clusters for the filtering collector and shredder categories. The zonal and clinal patterns reveal that there may be a weak upstream to downstream gradient within a single fluvial zone and almost discontinuity in contiguous tracts when the abiotic gradient changes suddenly.
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