The Patterns And Drivers Of Naturalization Of Alien Angiosperms:Insights From Darwin’s Naturalization Conundrum

The naturalization of species into various ecosystems worldwide is occurring at an unprecedented rate,resulting in the homogenization of the global flora.Therefore,understanding the patterns and mechanisms of global species naturalization has long been a central goal of ecological research.Darwin’s naturalization conundrum invokes the phylogenetic relatedness to explain the naturalization of alien species,by describing two seemingly contradictory hypotheses regarding that alien species with phylogenetic closely or distinctly related to native species are more likely to successfully naturalize.Reconciling the conundrum has gained increasing attention in recent years,with different studies often yield inconsistent results.Based on global and Chinese distributions of naturalized and native angiosperms,this study first explored the global patterns of the phylogenetic relatedness between naturalized and native species to test Darwin’s naturalization conundrum at a global scale.This study further tested the conundrum at different invasion stages.Furthermore,based on Darwin’s naturalization conundrum,this study explored how similarity in different ecological dimensions influences species naturalization,aiming to identify the specific dimension of similarity between the native and recipient regions that facilitates the naturalization of alien species.Based on the global distributions of 220,027 native angiosperms and 9,525naturalized angiosperms in 493 regions with area larger than 5,000km~2,this study analyzed the global pattern of phylogenetic relatedness between native and naturalized plants and tested how this phylogenetic relatedness varies with climate and human landscape modification.The results showed that,firstly,there was a latitudinal gradient in Darwin’s naturalization conundrum,that is,naturalized plants were more related to native plants at higher latitudes compared to those at lower latitudes.Secondly,temperature and seasonality were the primary drivers of global phylogenetic relatedness patterns.Naturalized plants with closely related to native plants were more likely to be naturalized in cold,dry,and seasonal climates.Moreover,human-induced landscape modifications resulted in even steeper latitudinal and temperature gradients in phylogenetic relatedness.This study highlights the importance of jointly considering the effects of climate and human activities on species naturalization when conducting cross-regional comparisons related to Darwin’s naturalization conundrum.Based on the distribution data of native angiosperms and alien angiosperms(including escaped,naturalized,and invasive angiosperms)across 32 provinces in China,this study explored the patterns of phylogenetic relatedness between alien and native plants across invasion stages.Furthermore,this study explored the impact of this phylogenetic relatedness on the success of alien species,as well as how this phylogenetic relatedness varies with climate and human landscape modification.The results showed that,firstly,in the early stages of invasion,alien plants closely related to native plants were more likely to successfully escape from cultivation into natural ecosystems,where they could both survive(that is,escape)and reproduce(that is,naturalize).Conversely,in later stage of invasion,invasive plants showed lower phylogenetic similarity to native plants compared to those in earlier stages.Specifically,naturalized species with a high phylogenetic similarity to native plants were more likely to successfully invade northwest China,while they faced greater challenges in achieving successful invasion in southern regions.Secondly,climate acts as the primary driver of the patterns in phylogenetic relatedness distribution.With the decreasing in mean annual temperature and annual precipitation,the phylogenetic relatedness between naturalized and native plants,as well as between invasive and native plants,becomes closer.This study reveals that the effectiveness of Darwin’s two opposite hypotheses is invasion stage-dependent and constrained by climatic factors.Based on the native and naturalized distributions of 9,907 naturalized angiosperms in 617 regions,this study explored the impact of ecological similarities and hierarchical differences between the native range and recipient regions on species naturalization.Specifically,for each naturalized species,similarity metrics were calculated in terms of climatic distance,compositional and phylogenetic dissimilarities of native flora,and the distance of the degree of human-induced landscape modification.The results showed that,on a global scale,similarity to the native range promoted species naturalization.Specifically,alien plants have higher naturalization probabilities in regions that share similar climates,species composition,and phylogenetic relatedness as their native range.Secondly,in environments with similar climatic conditions,species from regions with low human modification and high phylogenetic diversity were more likely to naturalize in regions characterized by lower diversity and more extensive human-induced landscape modifications.This study highlights the importance of considering various aspects of ecological similarities and hierarchical differences between native and recipient regions for understanding and predicting the global patterns of species naturalization.In conclusion,this study revealed the latitudinal gradient pattern of Darwin’s naturalization conundrum at the global scale,and clarified how climatic conditions and invasion stages affect the relationship between phylogenetic relatedness and species naturalization.Furthermore,this study revealed how various dimensions of ecological similarities and hierarchical distances between native and recipient regions would affect species naturalization.That highlights the important roles of climate matching,evolutionary matching and evolutionary imbalance in shaping naturalization success worldwide.These findings indicate that comprehensive consideration of latitude,climate,invasion stage,ecological similarity,and hierarchical distances can help resolve the long-standing debate on Darwin’s naturalization conundrum,and also provide important theoretical basis and decision-making support for the prediction and management of future ecological invasions.