LIFE-HISTORY AND SPECIES COMPOSITION OF THE DAMSELFLY ASSEMBLAGE ALONG THE URBAN TRACT OF A RIVER IN CENTRAL ITALY

The species composition of the damselfly assemblage and the life histo ry patterns of two Coenagrionidae (Ischnura elegans and Cercion linden i) were investigated along the urban tract of a river characterized by increasing organic pollution. The assemblage was dominated by general ist species, usually recorded in lentic habitats, rather than by typic al riverine species and the proportion of the latter decrease at the m ost polluted sites. At the end of Winter, the mean size and instar dis tribution were different between the sampling sites showing that the l ife history of both species examined were influenced by a degradation of the environmental quality. A longer reproductive period, absence of diapause, and tolerance of low oxygen concentration appear to be key factors that allow generalist species I. elegans and C. lindeni to pre dominate at the polluted sites.