Henri Tachet

Biomonitoring through biological traits of benthic macroinvertebrates: how to use species trait databases?

The aim of this paper was to investigate the potential use of biological and ecological traits of macroinvertebrates as indicator systems of quality conditions in freshwater ecosystems. To provide a framework for the trait analysis, a data base was developed; it stored biological information about 472 benthic macroinvertebrate taxa. Twenty-two variables describing biological and ecological traits were resolved into a number of simple attributes. A fuzzy coding procedure was used to describe the link between taxa and variables. Three strategies, using simple descriptive statistics or multivariate ordination techniques, were examined in their abilities to demonstrate some of the characteristics of the environment and to bring out clear information on the rate of changes in habitats. We used the Loire River, France, as a specific example. Like faunal analyses, trait analyses showed that a major change occurred in the community in the upper reaches of the river, but transition zones that were not detected with faunal data alone, were discriminated. They corresponded to differences in combinations of biological and ecological traits of communities and were linked to tributary influences (e.g. the Allier–Loire confluence) or anthropogenic disturbances: dams (Grangent, Villerest) or urban zones (Le Puy, Tours). We concluded that the species trait approach had the potential to evaluate the actual state of ecosystems, to discriminate among different types of human impact, and to develop monitoring tools considering the functional diversity of communities.

Net-Building Behaviour of Six Hydropsyche species (Trichoptera) in Relation to Current Velocity and Distribution along the Rhône River

A longitudinal succession of species of Hydropsyche along a stream continuum is a common pattern in Palearctic as well as in Nearctic regions. Using a laboratory channel, we studied the relationship between current velocity and six Hydropsyche species distributed from small streams to large rivers in the Rhône Basin (France). Different phases of net-building behaviour were used to test the reactions of larvae to variations in current speed over a range of 4-40 cm/s. Hydropsyche angustipennis had more than 30% of its larvae wandering at the end of the experiment and was the least adapted species to the experimental conditions; the proportion of wandering larvae for the other five species was less than 10%. The largest proportion of catchnets with regular meshes occurred at velocities between 28 and 40 cm/s for the upstream species (H. siltalai and H. angustipennis) and for a species of the middle reaches of stream (H. pellucidula). Another middle-reach species (H. exocellata) had the highest proportion of catchnets with regular meshes between 8 and 40 cm/s, and for the downstream species (H. contubernalis and H. modesta), this proportion occurred at 15 cm/s. Our results suggest that the species are ordered in a downstream sequence according to their ability to spin a normal catchnet when the natural current velocity decreases. Downstream species seem to be more tolerant than upstream species to low-velocity conditions that may occur over long periods in the lower reaches of large rivers.

A comparative description of the larvae of Psychomyia pusilla (Fabricius 1781), Metalype fragilis (Pictet 1834), and Paduniella vandeli Décamps 1965 (Trichoptera: Psychomyiidae) and comments on the larvae of other species belonging to these three genera

The morphology of the larvae of three French species of Psychomyiinae: Psychomyia pusilla, Metalype fragilis and Paduniella vandeli are described. A set of characters on the head, the prothorax, and the anal prolegs makes it possible to identify the larvae of the fourth and fifth instars. A brief study of the world distribution of the genera Psychomyia, Metalype, and Paduniella is presented. An examination of the larvae of these three genera from literature data and personal observations offered us the possibility to test the validity of the set of characters obtained for the three French species. A key (with comments) of the three genera is provided.