Non‐Native Species Alter Functional Diversity Worldwide: A Systematic Review of Competition, Predation and Habitat‐Mediated Effects in Freshwater Ecosystems

The introduction of non‐native species is one of the main threats to biodiversity and ecosystem functioning in freshwater environments, affecting the functional diversity of native communities. Functional diversity, based on phenological, physiological and morphological traits, is a crucial tool for understanding community structure and dynamics, particularly in the context of biological invasions. However, knowledge gaps remain regarding how these invasions impact functional diversity across different freshwater habitats.

In this study, we conducted a systematic review to synthesise existing knowledge on the impacts of non‐native species on the functional diversity of aquatic organisms in continental ecosystems such as lakes, rivers, floodplains and reservoirs. We followed the PRISMA protocol to ensure transparency and minimise biases in study selection, adhering to rigorous guidelines for searching, screening and including articles.

Our literature search in the Web of Science and Scopus databases yielded 1040 articles, of which 104 met all inclusion criteria. Additionally, we analysed temporal and geographical trends in studies addressing this topic. Our results indicate a significant increase in publications over recent decades, with the highest concentration in Europe, North America and South America. However, we identified a geographical bias, with fewer studies conducted in Africa and Oceania.

Most research is strongly biased toward fish and competitive interactions, often linked to functional homogenisation and trophic restructuring. In contrast, other groups remain underexplored, particularly regarding mechanisms like habitat modification and changes in resource quality, limiting a more comprehensive understanding across trophic levels.

Given the increasing threats to freshwater ecosystems, integrating trait‐based approaches into invasion biology is essential to improve predictions of ecological responses. By linking species traits to ecosystem processes, these approaches provide insights into changes in energy flow, nutrient cycling and community resilience, supporting more effective conservation and management strategies.