Ecological similarities and dissimilarities between donor and recipient regions shape global plant naturalizations

A central question in ecology is why alien species naturalize successfully in some regions but not in others. While some hypotheses suggest aliens are more likely to naturalize in environments similar to donor regions, others suggest they thrive in regions where certain characteristics are different. Using the native (i.e., donor) and recipient distributions of 11,604 naturalized alien plant species across 650 regions globally, we assess whether plants are more likely to naturalize in regions that are ecologically similar or dissimilar to their donor regions. Our results show that species are more likely to naturalize in recipient regions where climates are similar and native floras are phylogenetically similar to those of their donor regions, indicating that pre-adaptation to familiar biotic and abiotic conditions facilitates naturalization. However, naturalization is also more likely in regions with lower native flora diversity and more intense human modification than in the species' native range. Among all predictors, climate similarity and difference in native flora diversity emerge as the strongest predictors of naturalization success. In conclusion, ecological similarity in some factors but dissimilarity in others between donor and recipient regions promote the naturalization of alien plants and contribute to their uneven global distribution patterns.