Changes in caddisflies community composition and distribution along 60 years timespan monitoring in Luxembourg

Abstract

In Luxembourg, caddisflies have been systematically collected since the early Sixties. Three periods of exhaustive sampling may be distinguished: the Sixties; 1994 to 2002; and a long period from 2007 to the present time in the frame of the Water Framework Directive. Bearing in mind the uneven sampling procedure across periods, we aim to document changes in community composition and distribution through time including the nature of these changes (e.g. gains and losses of species). We hypothesise different trends of species gains and losses for specialist species in comparison to generalist species. Therefore, we propose a method to identify specialist and generalist species in our dataset. Historical data (1961 to 1968) lack information on precise locations and abundance of specimen collected. Consequently, cell grids of original distribution maps are used to compare caddisfly community assemblages along the three monitoring periods. We assess the changes that occur on presence/absence data in specific groups of species (i.e. cold-adapted, warm-adapted specialists and generalist species). Temporal β-diversity results reveal that survey intervals for each monitoring period are dominated by species losses when the comparison is restricted to cold-adapted species. On the other hand, warm-adapted and generalist species are increasing from the Sixties period when compared to the two next periods (1994–2002 and 2007–2020). However, the comparison of the most recent periods reveals species losses even for the warm-adapted and generalist species. This complex picture of caddisflies species losses and gains in different ways through time, amongst river types and in response to different pressures, is discussed.