Biological invasions and functional diversity: a comprehensive investigation in freshwater ecosystems.

Abstract

Biological invasions are one of the main threats to biodiversity and the functioning of freshwater ecosystems, affecting the taxonomic and functional diversity of native communities. Understanding these impacts is crucial for the management and conservation of freshwater ecosystems, especially in environments highly susceptible to invasions, such as floodplains. This thesis investigated the relationship between the introduction of non-native species and functional diversity in freshwater ecosystems, combining a global systematic review and two primary studies in the Upper Paraná River floodplain, Brazil. In the systematic review on the impacts of biological invasions on functional diversity in freshwater ecosystems, the analysis of 90 articles revealed an increase in publications on this topic in recent decades, although geographic and taxonomic gaps remain, with a research bias toward regions in North America, Europe, and South America. Moreover, most studies focus on fish and competitive interactions. The review highlighted the need for trait-based approaches to better understand and mitigate the impacts of biological invasions. In the primary research, it was analyzed the influence of species invasion, seasonality, and connectivity on the taxonomic and functional beta diversity of fish in the Upper Paraná River floodplain. Environmental factors, such as lagoon connectivity and seasonality, affected species and functional trait turnover. On the other hand, biotic factors, such as species richness and the occurrence of non-native species, influenced the richness component of beta diversity. The results indicate that the introduction of non-native species may increase beta diversity in the short term, but long-term studies are needed, as the introduction may promote functional and taxonomic homogenization, affecting ecological stability. In the investigation of the effects in lake area, depth, and isolation on native and non-native fish assemblages in the same floodplain, the results showed that lake depth had a stronger negative effect on species richness and abundance than lake area. Additionally, more isolated lakes had a higher abundance of non-native species, suggesting that isolation may favor their persistence by reducing predation pressure and providing suitable habitats for reproduction. This study emphasized the importance of considering environmental variables in understanding species distribution and managing invasive species. The findings of this thesis contribute to the understanding of the relationships between biological invasions and functional diversity, providing scientific support for more effective conservation and management strategies in freshwater ecosystems. The integration of taxonomic and functional approaches is essential to fully comprehend the ecological impacts of non-native species.