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Substrate heterogeneity influences the trait composition of stream insect communities: an experimental in situ study

Local distribution of stream insects is influenced by abiotic factors, such as substrate heterogeneity and amount of organic matter. We evaluated the influence of substrate heterogeneity on the functional structure and diversity of stream macroinvertebrate communities based on 4 traits: feeding habits, body size, body shape, and attachment to substrate. Heterogeneous substrate supported communities with higher functional diversity and richness than did homogeneous substrate. In addition, communities on heterogeneous substrate had more predators, shredders, filterer–collectors, and organisms with a large body size than did homogeneous substrate. In contrast, communities on homogeneous substrate had predominantly small organisms, case-builders, and scrapers. Our results suggest that in natural habitats, substrate heterogeneity selects specific combinations of traits especially related to size and feeding habit, which have strong implications for stream ecosystem functioning. As a result, one may anticipate that homogenization of stream bottom substrate associated with human activities should result in a reduction or loss of important functions linked, e.g., to the processing of organic matter, which should greatly affect the stream ecosystem.