Patterns of biological invasions in French freshwater systems by non-indigenous macroinvertebrates

Freshwater biodiversity is threatened by several mechanisms, of which the introduction of non-indigenous species and habitat alteration are the two most important. Exotic species act at various levels of organisation of macroinvertebrate communities, and are involved in different processes mediating their impacts on biodiversity, such as habitat modification or negative interactions with autochthonous fauna. The present work gives a list of the 43 French freshwater non-indigenous species, which represent 1.2% of the French freshwater macroinvertebrates. We provide their geographic origins, their distributions among zoological units by comparison with the native fauna and their functional characteristics according to a recent typology based on bio/ecological traits. An exponential trend of the cumulated number of non-indigenous species was evidenced, with a clumping of invaders within crustaceans and molluscs. Donor areas of non-indigenous species are in majority European, and the Ponto-Caspian basin is identified as the principal one. This pattern could be explained by a spread along waterways but its origin lies in a process of recolonisation of defaunated areas following several episodes of glaciation/deglaciation in Western Europe during the last 80,000 years. Finally, from a functional point of view, non-indigenous species exhibit a limited diversity, with two functional groups representing 80% of them.