The detection of exotic invasions‘ effects could thus depend on the spatial and biological detail level of the data used, so that some effects could be potentially overlooked or misinterpreted if the data is insufficiently detailed.įor example, fish introductions could enrich functional diversity at the regional scale, because, from a presence/absence perspective, they can increase regional species richness and consequently increase the number of functional traits present in that area 12. 6, 7), but extirpation, species substitution and decrease of native biomass have all been reported as a local result of exotic invasions 8, 9, 10, 11. While a lot of attention has been devoted to the consequences of exotic invasions on species taxonomic diversity at different geographical scales 5, hardly any regional extinctions have been recorded in aquatic taxa such as fish (with some notable exceptions, e.g. Among the causes of global biodiversity loss, exotic invasions are often placed at the top 3, 4, but mechanisms and impact of species invasions might vary in different ecosystems, taxa and spatial scales.
Overall, our results suggest that possible outcomes of severe exotic species invasions could include a reduced functional diversity of invaded communities, but analyzing data with finer ecological, temporal and spatial resolutions would be needed to pinpoint the causal relationship between invasions and functional diversity.īiodiversity is a key element of ecosystem functioning and characterizes its resilience to different pressures 1, but suffers from a general worldwide decline 2. Our results also showed that a lower diversity of ecological traits in communities (about half of less disturbed communities) corresponded to a high invasion degree, and that the exotic component of communities had typically less diverse ecological traits than the native one, even when accounting for stream order and species richness. These differences suggest that invasion dynamics could play a role in overriding some major environmental drivers. While functional diversity of native and exotic species responded similarly to most environmental constraints, we found significant differences in the effects of altitude and in the different ranking of constraints. We thus explored the connections between functional diversity and exotic species invasions, while accounting for their environmental drivers, using a fine-resolution large dataset of Mediterranean stream fish communities. a lower taxonomic diversity, but current knowledge on invasions effects underlined a potential increase of functional diversity. Exotic species invasions often result in native biodiversity loss, i.e.
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