Where are the alien species? Predictions of global plant species invasions under current environmental conditions and the human footprint.
Species invasion is a significant concern because of its substantial effect on native ecosystems. A number of species-specific invasion predictions that correspond to environmental conditions are available, but literature predicting global species invasion that corresponds to environmental conditions and human activity is scarce. In this study, the potential geographic ranges of 308 alien plant species were predicted under current environmental conditions and human activities. Environmental conditions were delineated by bioclimatic (mean annual temperature, mean annual precipitation, mean temperature of wettest quarter, and precipitation of driest quarter) and topographic variables (annual solar radiation and topographic wetness index). Human activity was delineated by the human footprint, which is a raster data layer created from nine global data layers that describe human population pressure, land use and infrastructure, and human access. The potential distribution of the target species was predicted using the different types of models. By searching the correlated literature, we identified and excluded the native geographic range of the studied species in the predicted geographic range to obtain the exclusive invasive range. Results demonstrated that the invasion hotspots included the southern part of North America, Southern and Western Europe, the south coast of Asia, coastal regions of Australia and New Zealand, the coast of West Africa, the Ivory Coast of Africa, and the southern part of Brazil. In addition, the land areas of the low- (proper for less than 50 alien species), moderate- (51-100 aliens), and high-risk regions (more than 100 aliens) are 213.23, 18.15, and 2.50 million km2, respectively. All variables (bioclimatic and topographic variables and human footprint) were positively correlated with increasing richness of alien species. The highest correlation coefficient was obtained for the human footprint.