Influence of Environmental Variables on Stream Caddis Larvae in Three Slovenian Ecoregions: Alps, Dinaric Western Balkans and Pannonian Lowland

Abstract

AbstractIdentification of the environmental variables that influence caddis larvae was performed on 504 samples collected at 94 sites within the three ecoregions of Slovenia; the Alps, the Dinaric western Balkans and the Pannonian lowland. Canonical Correspondence Analysis (CCA) was performed to find sig‐nificantly influential variables and compare their absolute and relative importance in structuring caddisfly assemblages in the different ecoregions. Altogether, 234 variables were considered. According to their type of influence on organisms, variables were classified as indirectly influential variables (e.g., altitude), and directly influential variables or ecological factors (e.g., temperature). Caddis larvae responses were characterized as log abundances of 132 taxa, of which 126 were identified at the species level. The absolute and relative influences of the same environmental variable were found to be different in the selected ecoregions. Of the ecological factors, temperature (maximum and range) was found to be the most important in both mountainous ecoregions (Alps and Dinaric western Balkans). In the Pannonian lowland ecoregion, periodicity was the most influential factor. Of the indirectly influential variables, those that were good predictors of caddis larvae assemblages in the mountainous ecoregions were relatively unimportant in the Pannonian lowland ecoregion. Differences among ecoregions were also found in the cumulative explained variation in the caddisfly distribution, which was the highest in the Alps and the lowest in the Pannonian lowland. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)