Exotic species invasions undermine regional functional diversity of freshwater fish

Marco Milardi,Giuseppe Castaldelli,Janne Soininen,Anna Gavioli

doi:10.1038/s41598-019-54210-1

Marco Milardi, Giuseppe Castaldelli + Show 2 more

Open Access

https://doi.org/10.1038/s41598-019-54210-1

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Abstract

Exotic species invasions often result in native biodiversity loss, i.e. a lower taxonomic diversity, but current knowledge on invasions effects underlined a potential increase of functional diversity. 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. 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. These differences suggest that invasion dynamics could play a role in overriding some major environmental drivers. 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. 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.

Highlights

Exotic species invasions often result in native biodiversity loss, i.e. a lower taxonomic diversity, but current knowledge on invasions effects underlined a potential increase of functional diversity
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, but extirpation, species substitution and decrease of native biomass have all been reported as a local result of exotic invasions[8,9,10,11]
boosted regression tree (BRT) analysis showed that environmental variables typically had different magnitude and direction of relative influence on exotic and native species functional diversity (Fig. 1)

Summary

Introduction

Exotic species invasions often result in native biodiversity loss, i.e. a lower taxonomic diversity, but current knowledge on invasions effects underlined a potential increase of functional diversity. While functional diversity of native and exotic species responded to most environmental constraints, we found significant differences in the effects of altitude and in the different ranking of constraints. These differences suggest that invasion dynamics could play a role in overriding some major environmental drivers. Taxonomic homogenization would affect functional diversity of invaded areas, as it leads to communities with a lower number of species and a lower variety of traits, but it remains unclear whether this is a significant element of exotic invasions. The variable abbreviations stand for: Long – longitude, Lat – latitude, Alt – altitude, NH4+ – ammonia, BOD – biological oxygen demand, TSS – total suspended solids, T – water temperature, NO3 – nitrate nitrogen, COD – chemical oxygen demand, EC – electrical conductivity, TP – total phosphorus, Agric – agricultural, Other nat – other natural area, Freshw – freshwater, Forest – forest, Urban – urban and Brackishw – brackish water

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