Human activities are eroding natural dispersal barriers, providing species with opportunities to expand beyond their native distributions. Outcomes from such introductions vary greatly: some species fail to establish outright, and even those that become naturalized find different degrees of success in newly occupied regions. Understanding the success of alien species can aid in predicting future invasions, but can also provide insights into the dynamics underlying natural range expansions. However, invasiveness encompasses multiple measures of ecological success, prompting the recent adoption of schemes for classifying species along three distributional ‘dimensions’ of invasiveness: extent, abundance, and habitat breadth in the naturalized range. While this framework recognizes the possibility for species to attain different ‘types’ of invasiveness, many concepts in ecology suggest links among the dimensions of species distributions. Here, we combine data from over one million vegetation surveys spanning Europe with a global database of alien plant distributions to quantify dimensions of invasiveness in Europe’s alien flora. We test whether invasiveness dimensions covary, or whether species achieve invasion success in different ways. In addition, we explore drivers of each invasiveness dimension, asking if functional traits, habitat preference, or region of origin predict different types of invasion success.
Results/Conclusions
We find that most naturalized plants in Europe fall along a continuum from overall poor invaders to super invaders – species excelling in all three dimensions. The extent and abundance dimensions had the strongest link, with few species becoming widespread without achieving high local abundances in their naturalized range. Consistent with an important role of enemy release in the invasion process, aliens introduced from outside of Europe were more abundant and widespread than aliens introduced from elsewhere within the continent. However, this effect was dependent on functional traits: species investing in acquisitive growth strategies, those thought to be most vulnerable to biotic constraints in their native ranges, were the most successful invaders when introduced from afar. Taken together, our results indicate that dimensional characteristics of alien distributions are similar to those of native distributions, suggesting that similar forces constrain both. Alien species demonstrating high success at local scales (i.e. reaching high abundance in a variety of habitats) present the greatest risk for expanding their naturalized range.