Investigating biological invasion hypotheses in aquatic plant communities from a subtropical reservoir based on phylogenetic diversity

Evolutionary relatedness influences interactions between invasive and native species and underpins hypotheses such as biotic resistance and Darwin’s naturalization. However, these relationships, which vary across spatial scales, remain poorly explored in human-made aquatic environments. We investigated how the phylogenetic structure of native macrophyte communities are associated with the establishment of the invasive grass Urochloa arrecta , using 2.736 records from the Itaipu Reservoir (1.350 km²) collected between 2022 and 2024. A total of 743 sampling sites were analyzed, of which 502 were invaded. We examined co-occurrence patterns and phylogenetic distances between the invader and native species, as well as the relationships between the invasive occurrence and the species richness, phylogenetic structure and lineage turnover at two spatial scales: the entire reservoir and its tributaries. U. arrecta showed positive co-occurrence with closely related native grasses and negative associations with distantly related taxa. At the reservoir scale, species richness was negatively related to invasion, whereas phylogenetic structure was not significantly related to it. At the tributary scale, invaded upstream communities exhibited lower richness and greater phylogenetic divergence, whereas near the dam these patterns were weak or absent. Phylogenetic turnover was consistently lower in invaded sites across scales, indicating reduced lineage replacement and a pattern consistent with biotic homogenization. These findings suggest that U. arrecta establishes preferentially alongside closely related native species, contradicting Darwin’s naturalization hypothesis, and that biotic resistance is scale and context dependent. The observed homogenization underscores the need to incorporate phylogenetic metrics into management strategies to mitigate community vulnerability to invasion.