Naturalization and invasion of alien plants in Puerto Rico and the Virgin Islands

A fundamental goal in invasion ecology is to identify and understand the factors explaining why some alien species become invasive when others fail. In this study we gathered data on taxonomy, invasive status, invasion history, geographic distribution, and biological and ecological traits of 1,032 alien plant species occurring on different habitats in Puerto Rico and the Virgin Islands. These data were used to evaluate the relative importance of habitat and species attributes in influencing the likelihood of alien plants to become naturalized and subsequently invasive on these islands. Our results showed that alien species were more likely to become naturalized if they grow in semi-natural habitats, have large native distribution ranges, long residence time, were introduced for horticulture and have mixed breeding systems. On the other hand, naturalized species were more likely to become invasive if they were introduced for horticulture, behave as weeds, have tolerance to different climatic life-zones, thrive in ruderal habitats, have mixed breeding systems with hermaphroditic flowers, reproduce vegetatively and produce small seeds. Whereas some of these parameters were important for both transitions, others were important for either naturalization or invasion. Overall, our results emphasize the importance of studying different stages of the invasion process in order to understand the mechanisms explaining successful invasions rather than baseline approaches of simply comparing invasive with natives or noninvasive alien species. Understanding the process by which alien species become naturalized or invasive could provide a more objective and accurate approach for managing and predicting biological invasions.