Ecological Impacts of Invasive Species

Abstract

Biological invasions represent one of the primary drivers of native biodiversity loss globally, yet the ecological impact mechanisms of invasive species vary substantially across taxa, ecosystems, and invasion stages. This study conducted a multi-taxon, multi-ecosystem assessment of invasive species ecological impacts across 84 Central European freshwater, grassland, and forest sites, quantifying the effects of eight invasive species -- American mink (Neovison vison), signal crayfish (Pacifastacus leniusculus), raccoon (Procyon lotor), Japanese knotweed (Reynoutria japonica), Himalayan balsam (Impatiens glandulifera), grey squirrel (Sciurus carolinensis), nutria (Myocastor coypus), and topmouth gudgeon (Pseudorasbora parva) -- on native species richness, abundance, and functional diversity across paired invaded versus uninvaded control sites (2019-2023). Mean native vertebrate species richness was 38.4 +/- 8.4% lower at invaded sites, with the greatest reductions in freshwater macroinvertebrate communities (54.8 +/- 12.4% reduction at signal crayfish sites), waterbird assemblages (42.4 +/- 9.4% at American mink sites), and riparian plant communities (48.4 +/- 10.4% at Japanese knotweed sites). Functional diversity (FRic) declined by 44.8 +/- 8.4% at invaded sites, exceeding taxonomic richness declines in all taxa. Invasion impact was significantly moderated by invasion duration (r = -0.68, p < 0.001), native community diversity (r = -0.58, p < 0.001), and landscape connectivity (r = -0.48, p < 0.001). An Invasion Impact Score (IIS) integrating native diversity loss, functional impact, and ecosystem process disruption ranked signal crayfish and Japanese knotweed as the highest-impact invasive species in the study region, with direct implications for management prioritisation under the EU Invasive Alien Species Regulation