Accurate description of the abundance of taxa and their biological traits in stream invertebrate communities: effects of taxonomic and spatial resolution

Studies of biodiversity and ecosystem function require to consider the iden tification level that accurately describes the functional diversity of comm unities, in terms of their biological traits, at different spatial scales. Therefore, we combined three published data sets of stream macroinvertebrat e abundances collected at three spatial scales with a database of functiona l species traits (e.g. life history, morphology, physiology, and behaviour) . We investigated the abundance of taxa and their traits at five levels of taxonomic (from species to class) and three levels of spatial resolution (f rom local habitat to catchment). We used multivariate analyses and correlat ions to evaluate the accuracy of community descriptions through the stabili ty of such descriptions, the degree of similarity of site ordinations, and the overall community structure expressed at each taxonomic level. The accu racy of community descriptions based on the abundance of taxa depended on t he spatial scale considered. The accurate description of the abundance of t axa required identifications to genera and/or families on the local habitat scale, while species identifications were needed on the catchment scale. I n contrast, the accurate description of the abundance of biological traits was achieved by identifications to species, genera, or families on all thre e spatial scales. Thus, species identifications may not be necessary for fu ture studies on the functional diversity of the stream benthos at different spatial scales.