Patterns of benthic invertebrate assemblages in rivers of Central Italy

The present paper aims to analyse and compare the benthic composition of several rivers of Northern, Central Apenninic and Southern Italy. We considered faunistic data from seven Italian streams (Adige, Mignone, Arrone, Fiora, Aniene, Amaseno and Simeto rivers). In particular, we wanted to compare how, using detailed taxonomic data, every single river or stretch of river would conform or differentiate from other rivers (or stretches of river) in respect to their faunistic and structural aspects. We used presence-absence data of taxonomic groups, identified mainly at species level. Similarity indexes, Principal Component Analysis and divisive analysis (DIVA) gave almost overlapping results. Aggregative, ordination and divisive algorithms, in fact, group each of the studied rivers as single independent units, isolated and differentiated from the others. We discuss the results with respect to the main longitudinal zonation theories on running waters.