Close relatives are better invaders

The number of exotic plants naturalized in the United States far exceeds that of any other group of organisms. In this study of Cardueae thistles, researchers used GBIF-mediated occurrences to do ecological niche modelling of non-native species in the California Floristic Province. Results showed that the more closely related introduced thistles are to native species, the more likely they are to be invasive. Successful invaders also showed greater levels of niche overlap with native thistles than non-invasive species. The study also examined traits related to dispersal properties, finding that invasive thistles have longer bristles, and shorter and lighter seed than non-invasive counterparts. The conclusions make a case against Darwin’s naturalization hypothesis, supporting the idea instead that plant invaders closely related to native species are not at a disadvantage.