Biogeographic origins and drivers of alien plant invasions in an oceanic archipelago

Abstract

Understanding the historical and contemporaneous determinants of invasion success in island systems can help to decisively contribute to identifying sources and designing strategies against the scenarios that are more likely to give rise to new invaders. Herein, we investigate the origins of the invasive alien flora of the Canary Islands, with emphasis on the mechanisms shaping its spatial organization within the archipelago. An updated checklist of the invasive alien flora of the Canary Islands was compiled together with key complementary information, including native biogeographical regions, stage of invasiveness, and dates of naturalization. Our updated list includes 149 alien plant species with a certain degree of invasiveness. The Neotropics stood out as the region providing the highest number of invasive species, followed by the Cape Region, tropical Africa, and the Mediterranean Basin. We observed a slow but steady increase in numbers of invasive species until the 1950s, followed by a stronger rise thereafter. Among various possible mechanisms, we reveal that climatic similarity seems to best explain patterns of composition dissimilarity within the invasive flora among islands. Interestingly, the Neotropical region stands out as the main source of plant invasions to the Canary Islands, outnumbering those from other regions with a Mediterranean-type bioclimate, emphasizing the importance of historical trade networks. Our study brings attention to the importance of archipelago dependent assessments of the underlying mechanisms that contribute to plant invasion success in oceanic archipelagoes.