RISPOSTA DELLA COMUNITA’ BENTONICA AD UN GRADIENTE LONGITUDINALE IN TRE TORRENTI MONTANI

The identification and explanation of spatial gradients of biotic organisation have long been key objectives in the field of stream ecology (Illies & Botosaneanu, 1963; Hynes, 1970). High-gradient mountain streams are ideal for studying longitudinal biological patterns, although the degree of similarity in the biological gradient among physically similar streams in a region is poorly known (Finn et al., 2005). Our first objective was to evaluate intra- and inter- habitat variability in benthic communities spatial response along three streams in the Dolomiti Bellunesi National Park. We analyzed the relative influence of longitudinal position versus reach-scale physical variables on community structure and evaluate community environmental similarity at comparable longitudinal positions on the three streams. Our results confirmed the different position of springs and streams along the longitudinal gradient, the sampling of the spring microhabitat underline that the spatial response of benthic communities are influenced by habitat typology, underling the importance to consider the heterogeneity of this stream reach also for the sampling methodology (Costa et al.,2008). Both intra and inter habitat result show that Headwater characteristics are more heterogeneous from how predict by the classic models (Vannote et al., 1980): even if the longitudinal position (altitude) is not secondary in the explanation of the results, in each streams the environmental characteristics and the spatial response of macrobenthos community don’t follow the continuum, and at the comparable altitudes are more heterogeneous than how generalized by the classic theories (Vannote et al., 1980, Minshall et al., 1983, 1985). The results in the Mis confirm that also the connectivity (Ward 1989, Pringle 2003/b) is an important factor to consider in the studies of zoobenthos communities. Today is necessary and important improve the knowledge on Headwater because, at the moment, the classical model, accepted also from this part of river network, even if consider an acceptable generalization of these ecosystems, in the practice they don’t reflect the real environmental characteristics and benthos communities structure (Poole, 2002, Thorp et al., 2006). The right comprehension of Headwater is an important key in the steam ecology, both for improve general understanding about this systems, than for its protection, because as known, these systems are among the ecosystems interested from direct (abstraction) and indirect (climatic change)(Barquin et al., 2008)