Biotic homogenization (BH), characterized by an increase in similarity, occurs when common species are widely introduced or native species are extirpated. This process is particularly concerning from a conservation perspective because it can reduce biodiversity, diminish ecosystem resilience to environmental changes, and lead to the loss of unique ecological functions associated with endemic species, thereby eroding regional uniqueness. The trend of BH is already evident in water bodies across the European continent, where the introduction of non-native fish species has significantly altered native ecosystems. Here we evaluated the compositional and functional changes of fish assemblages across 18 lentic water bodies in Greece (southeastern Balkans) between the present and 120 years ago. We utilized the Jaccard similarity index and functional diversity metrics (the difference in functional richness-ΔFric, functional beta-diversity-Fdiv, functional turnover-Ftur, and functional nestedness-Fnes). Our results underscored an ongoing compositional homogenization, largely attributable to the introduction of generalist, non-native species such as Cyprinus carpio, Carassius gibelio and Gambusia holbrooki. These species, along with others like Pseudorasbora parva and Lepomis gibbosus, have not only reshaped the biodiversity of the studied aquatic ecosystems but have also altered their functional dynamics. While taxonomic homogenization was prominent, functional changes were more complex. Fuctional richness (Fric) was higher in most present assemblages indicating a gain in species traits. The range of Fdiv values indicated considerable variability in the shifts of species' functional traits, with some ecosystems showing high levels of functional turnover (Ftur), particularly in certain lakes, suggesting a notable replacement of native traits by those of introduced species. Meanwhile, Fnes values indicated a moderate level of nestedness, where current assemblages retain many functional characteristics of their pristine counterparts, although new traits have emerged, and some have been lost. This study enhances our understanding of biotic changes in southern European freshwaters and highlights a potential risk to their compositional diversity and functional stability, particularly if the rate of these changes accelerates in the near future. Therefore, it is crucial to implement conservation measures to protect this unique fish fauna. Graphical abstract

Compositional and functional changes within Greek (southeastern Balkans) lentic fish assemblages

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发表日期：

2025年2月22日

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Olga Petriki,
Dimitra C. Bobori

摘要

Biotic homogenization (BH), characterized by an increase in similarity, occurs when common species are widely introduced or native species are extirpated. This process is particularly concerning from a conservation perspective because it can reduce biodiversity, diminish ecosystem resilience to environmental changes, and lead to the loss of unique ecological functions associated with endemic species, thereby eroding regional uniqueness. The trend of BH is already evident in water bodies across the European continent, where the introduction of non-native fish species has significantly altered native ecosystems. Here we evaluated the compositional and functional changes of fish assemblages across 18 lentic water bodies in Greece (southeastern Balkans) between the present and 120 years ago. We utilized the Jaccard similarity index and functional diversity metrics (the difference in functional richness-ΔFric, functional beta-diversity-Fdiv, functional turnover-Ftur, and functional nestedness-Fnes). Our results underscored an ongoing compositional homogenization, largely attributable to the introduction of generalist, non-native species such as Cyprinus carpio, Carassius gibelio and Gambusia holbrooki. These species, along with others like Pseudorasbora parva and Lepomis gibbosus, have not only reshaped the biodiversity of the studied aquatic ecosystems but have also altered their functional dynamics. While taxonomic homogenization was prominent, functional changes were more complex. Fuctional richness (Fric) was higher in most present assemblages indicating a gain in species traits. The range of Fdiv values indicated considerable variability in the shifts of species' functional traits, with some ecosystems showing high levels of functional turnover (Ftur), particularly in certain lakes, suggesting a notable replacement of native traits by those of introduced species. Meanwhile, Fnes values indicated a moderate level of nestedness, where current assemblages retain many functional characteristics of their pristine counterparts, although new traits have emerged, and some have been lost. This study enhances our understanding of biotic changes in southern European freshwaters and highlights a potential risk to their compositional diversity and functional stability, particularly if the rate of these changes accelerates in the near future. Therefore, it is crucial to implement conservation measures to protect this unique fish fauna.

Graphical abstract