Widespread freshwater non-native fishes exhibit synchronized population dynamics with functionally similar natives.

Invasive non-native fish species can profoundly disrupt ecosystems. In invasion ecology, using the functional similarity with native species to help predict demographic rates of non-native species and infer the ecological processes underlying it remains largely unexplored. Utilizing a comprehensive analysis of 2,903 species pairs across 153 sampling sites in rivers distributed in different continents, we evaluated interspecific synchrony patterns among populations of native and non-native fish species and explored their relationship with functional and phylogenetic dissimilarities using a linear mixed model. Our results indicate that non-native fish exhibit higher synchrony with native species that share similar ecological and morphological traits. This finding corroborates our hypothesis that co-occurring non-native and native species that are more functionally similar are more synchronized and emphasizes the importance of environmental filtering significantly shaping population dynamics between native communities and coexisting non-native species. We highlight the potential of widespread non-native species in increasing synchronous patterns and consequently decreasing community stability. By elucidating which type of dissimilarities (ecological, life history, morphological, and phylogenetic) can predict synchrony and which ecological mechanisms facilitate the coexistence of native and non-native species, this research underscores the ecological implications of invasion dynamics in the long term and helps to guide conservation efforts.