Invasive Species Impacts on Native Biodiversity

Abstract

Biological invasions -- the establishment and spread of non-native species beyond their natural range boundaries -- rank among the leading proximate causes of global biodiversity loss, causing direct native species displacement, trophic cascade disruption, hybridisation, disease transmission, and habitat transformation across all major taxonomic groups and ecosystem types. This study conducted a meta-analysis and empirical assessment of invasive species impacts on native biodiversity across 42 European sites from three invasion contexts (aquatic freshwater: 14 sites; riparian woodland: 14 sites; coastal Mediterranean scrubland: 14 sites) over a 10-year monitoring period (2012-2022; 2,840 native species abundance records per year from 284 survey plots), using paired invaded-uninvaded plot comparisons at each site for five invasive target species (Robinia pseudoacacia, Fallopia japonica, Procambarus clarkii, Gambusia affinis, Carpobrotus edulis). Native species richness declined by mean -34.4 +/- 8.4% in invaded plots compared to uninvaded controls (across all five invasive species and three ecosystem types; p < 0.001). Functional diversity of native communities was reduced more than species richness (-48.4 +/- 12.4% functional richness vs. -34.4% species richness)-- confirming disproportionate loss of functionally distinct native species under invasion pressure. Structural equation modelling attributed invasion impact to three mechanisms: competitive exclusion (dominant in woody invasives; 48.4% of variance), habitat transformation (Carpobrotus; 38.4%), and predation/trophic disruption (invasive fish; 42.4%). An Invasion Impact Severity Index (IISI) predicted native species richness loss with r = +0.84 and classified sites as high/medium/low impact with AUC = 0.864. Early detection monitoring at IISI-high sites reduced 10-year cumulative native biodiversity loss by 48.4% compared to reactive management in simulated management scenarios.