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Résumé :
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The effect of microhabitat on the chironomid (Diptera) community of a large river was tested by trapping floating pupal exuviae after emergence of adults. The spatial distribution of the 33 species or groups of species that were identified was strongly explained by mean particle size, porosity and heterogeneity of substratum. A study of the size, means of respiration, mode of life and feeding habits of the species showed that the substratum-faunal relationships could be explained in part by biological traits of the species present. Two gradients could be defined on the basis of habitat variables: a substratum porosity gradient that was significantly correlated with species richness and diversity, and a second gradient related to particle size that was significantly correlated with biological categories.
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