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Using structural and functional differences in stream invertebrate communities between Mediterranean and temperate regions for anticipating the implications of climate changes

Dolédec Sylvain

Mediterranean stream invertebrates have to face high seasonal discharge patterns including predictable torrential floods and severe droughts. In contrast, discharge is less variable in temperate streams and intermittent flow conditions remain fairly uncommon. Hydroclimatic models predict that climate change will increase the frequency and severity of extreme events across Europe. A possible consequence might be an increase of the proportion of streams having Mediterranean characteristics in actual temperate regions. Therefore, understanding the actual ecological differences between Mediterranean and temperate streams may help to anticipate large-scale ecological impacts of climate change. Given that large-scale factors act as filters for local community composition, we hypothesized that climatic differences between Mediterranean and temperate regions should affect the taxonomic and biological trait composition of stream communities. We assembled the abundance of 326 stream macroinvertebrate genera of 265 sites each from the Mediterranean Basin and from temperate Europe and linked these abundances to published information on 61 categories of 11 biological traits reflecting the potential of resilience and resistance to disturbances and general functions of invertebrate genera. Though regional taxonomic richness was higher in the Mediterranean region, local taxonomic richness and diversity did not significantly differ between regions. By contrast, local trait richness and diversity were significantly higher in the Mediterranean region. Both local taxonomic and trait community composition differed between regions, but the former varied much more than the latter, highlighting that climate change could produce large changes in the taxonomic composition of temperate streams but rather weak changes in their trait composition. Macroinvertebrate genera (especially Coleoptera, Heteroptera and Odonata) in the Mediterranean region generally demonstrated high dispersion and colonization capabilities, suggesting that species loss in the temperate region, by extinction or northward emigration of taxa, would be rapidly compensated by the immigration of highly mobile southern Mediterranean taxa. Thus, climate change would likely have stronger implications for the local conservation of taxa than for the trait composition of stream macroinvertebrate communities and the general functioning of streams.