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Aim: Most studies focusing on terrestrial ecosystems have shown that non‐native species are more likely to invade phylogenetically clustered communities, that the introduction of non‐native species increases phylogenetic clustering in the recipient communities, and that the latter is more conspicuous for recipient communities at a larger spatial scale. However, whether these patterns hold for aquatic ecosystems is rarely tested. Here, we investigate the phylogenetic structure of native and non‐native freshwater fish assemblages at a continental spatial extent. Location: The continental United States and Canada. Time period: Current. Methods: We collated native and naturalized non‐native species lists of freshwater fishes for each watershed at local and regional spatial scales. Two phylogenetic metrics (MPDses and MNNDses) representing different evolutionary depths were used to quantify the phylogenetic dispersion of each watershed fish assemblage and were related to temperature and precipitation using correlation and regression analyses. Values of the metrics were compared between the two spatial scales. Results: Our study found that (1) phylogenetically more diverse fish communities tended to be invaded by fewer non‐native fish species, and that non‐native species more frequently invaded communities with lower phylogenetic dispersion (i.e. higher phylogenetic clustering), (2) introduction of non‐native fishes reduced phylogenetic clustering in some watershed but increased clustering in others, (3) introduction of non‐native species caused phylogenetic dispersion to increase in watersheds with low phylogenetic diversity and to decrease in watersheds with high phylogenetic diversity and (4) phylogenetic clustering for fish assemblages at the larger spatial scale was smaller than that at the smaller spatial scale. Main conclusions: Support for Darwin's naturalization and preadaptation hypotheses in freshwater fish assemblages depends on the phylogenetic diversity of assemblages within the invaded watersheds. Our results are contrary to previous studies that found that the introduction of non‐native species increases phylogenetic clustering in the recipient communities more strongly at a larger spatial scale. [ABSTRACT FROM AUTHOR]

Aim: A better understanding of native and non‐native species responses to environmental conditions, historical processes, and human pressures is crucial in the face of global environmental changes affecting biodiversity. Here, we evaluate the relative roles of environmental, historical and anthropogenic factors in influencing species richness of native and non‐native freshwater fishes in watersheds across North America. Location: North America (exclusive of Mexico). Time period: Recent. Major taxa studied: Freshwater fishes. Methods: We compiled an extensive dataset of native and non‐native fish richness in 2,993 watersheds across North America, together with corresponding data for environmental (climatic, geographic), historical and anthropogenic factors. We used variance partitioning and hierarchical partitioning to quantify the relative importance of environmental, historical and anthropogenic factors in explaining richness variation in native and non‐native [overall, and by geographic origin (foreign/translocated) and pathway (authorized/unauthorized)] fishes, while accounting for correlations among explanatory variables and spatial autocorrelation. Results: Overall importance of environmental and anthropogenic factors was greater than historical factors in explaining both native and non‐native richness. Precipitation‐related factors were more important in explaining native richness, whereas non‐native richness was largely associated with temperature‐related factors. However, richness related to authorized introductions was less constrained by temperature than unauthorized introductions. Dam density, road density and urbanization gradient were major anthropogenic factors related to non‐native richness, yet their relative importance varied among origin‐ and pathway‐based categories. Conclusions: Our findings indicate different environmental drivers influence native and non‐native fish richness patterns in North America. The accumulation of non‐native species in watersheds depends on the interaction between environmental conditions and anthropogenic‐based processes related to introduction history including geographic origin, introduction pathway, and propagule pressure, where the latter likely plays a major role. Warmer regions with high human population densities and more impoundments are more prone to fish invasions, mostly via unauthorized introductions. [ABSTRACT FROM AUTHOR]