Phylogenetic Relatedness Predicts Extinction Risk of Native Freshwater Fishes From Non-Native Fishes Across a Latitudinal Gradient

The strength of the interspecific interactions between non-native and native species influences the subsequent invasion impacts, with stronger interactions and thus more severe impacts predicted when the species are phylogenetically close and co-exist at lower latitudes. Although work demonstrates non-native fish are more likely to invade areas which have phylogenetically closely related species present, the impacts of these invaders on the native species remain poorly understood. Accordingly, we conducted a comprehensive analysis of global freshwater fish occurrence data to test the phylogenetic niche conservatism hypothesis in co-occurring native and non-native freshwater fishes, assess whether non-native fishes drive extinctions of phylogenetically closely related native species, and evaluate how this varies with latitude. Phylogenetic niche conservatism was evident in co-occurring non-native and native fishes, with their morphometric trait dissimilarity significantly correlated with their phylogenetic distance. Extinct freshwater fishes were found to be more closely related to co-occurred non-native species than were species of other conservation statuses. However, the relationship between the extinction probability of native freshwater fishes and their phylogenetic relatedness to non-native species was context-dependent, varying with latitude and across biogeographical realms. At higher latitudes, native fishes closely related to non-native species had a higher probability of extinction, whereas at lower latitudes, closely related native species were less likely to become extinct. Thus, the extinction risks posed by non-native fish vary spatially and depend on their phylogenetic relatedness to native species, both of which are recommended for consideration in invasion risk management programmes.