Climate change, land use, and intercontinental biotic invasions

Background/Question/Methods Biotic invasions can affect ecosystem performance.  Knowing the source region, invasion pathways, traits, and performance in native habitats relative to exotic regions of invasive species, and how climate and human activity might affect these species, is critical for management.  Most studies have been conducted in recipient regions only, and the patterns and factors responsible for invasion success on continental scales around the globe are not clear. A powerful tool to tackle such issues would be to conduct reciprocal comparisons of introduced species between the native and exotic regions.  Here, we analyze the distributions of plants introduced among major continents to test whether and to what extent the invasion success is linked to native diversity, landforms, human activity, and climate change and to predict how climate change might affect the future spread of the exotics.  The data are based on extensive search from the published materials.  Species distribution on each continent is calculated as the proportion of geographic units the species occupied.  
Results/Conclusions Distributions of exotic plants highlight the influence of history, geography, and human activity.  (1) Species introductions among continents are clearly asymmetrical in both the number of exotics and in their relative success (e.g., North America has received far more non-native species than it has exported).  (2) Plants consistently have broader distributions in their native ranges than elsewhere.  (3) The distribution of exotics in recipient regions highly reflects the characteristics in their native regions.  (4) The spread is constrained to a greater degree in some continents than in others.  (5) The average areas of species ranges within native regions are inversely related to the diversity of the region.  (6) Landforms appear to play a role in altering the pathways and rates of invasions.  Overall, eastern Asia with the E-W oriented mountain ranges, more complex landforms, and diverse flora seems to resist the spread of exotic plants more effectively than North and South America, especially under the dramatically changing climates.  By knowing the extent to which exotic species are restricted to human-altered environments or have penetrated natural communities in each region, we can identify the relative role of climate, land-use, and species traits.  Further comparisons are needed in the future to examine the relationships of introduced species in both their native and exotic regions.