Potential distribution of invasive alien species in the upper Ili river basin: determination and mechanism of bioclimatic variables under climate change

Controlling alien species invasion requires a full understanding of the potential distribution of alien species and the functions of key environmental factors that influence such distribution. In this study, potential distributions of 28 invasive alien species under current and future bioclimatic conditions at the upper Ili river basin (the Chinese part of the basin) were predicted, and the important bioclimatic variables that determine the distributions were examined. Under the current conditions, the number of alien species ranged from 0 to 10, and the eastern part of the basin may not be influenced by invaded species. Under future conditions, 0-22 alien species may find these areas suitable for invasion. The potential distributions of invasive plant species were determined mainly by precipitation-related bioclimatic variables, whereas temperature-related variables were relatively more relevant for animal species. Bioclimatic conditions during the coldest and/or driest month (or quarter, which is a period of 3 months) may significantly affect potential distributions for both plant and animal species. Quantified analysis demonstrated that the number of species is likely to increase considerably with the increase in precipitation during the driest month, particularly with a variation of >3 mm in the precipitation during the driest month. More alien species may invade regions where the precipitation during the driest quarter under future conditions is 10 mm higher than the current conditions. The effect of precipitation during the coldest quarter on species invasion is similar to that of precipitation during the driest quarter: the higher the precipitation during the driest quarter under future conditions (more than 9 mm than that under current conditions), the higher will be the rate of alien species invasion in the study area.