Human activity positively associated with the risk of spread of the giant African snail (Lissachatina fulica) recently reported in central and northern China

The highly invasive giant African snail (Lissachatina fulica), one of the most damaging mollusk species in the world, damages over 500 plants and threatens conservation of endemic snails. It widely spreads in southern and southeastern China after a century of invasion. Existing niche-based species distribution models predict that this mollusk species is unlikely to distribute in central and northern China. However, recent reports identify its occurrence in 10 populated cities within central and northern China likely due to human-mediated processes, though the associated risk of spread remains undetermined. To test if human activity is a key factor for the risk of spread of the giant African snail in these cities, we compiled 247 occurrence records of the giant African snail in the Eurasia biogeographic region, and built zero-inflated Poisson, random forest, and k-nearest neighbor models with habitat condition and human activity as explanatory variables. We used the fitted models to predict the present and project the risk of spread under four climate change scenarios in the 2030 s and the 2050 s. The results show that human population density is positively associated with the risk which also varies by the types of land use. Difference in precipitation between the wettest and the driest months and elevation are negatively associated with the risk. However, there is no projected increase in the risk of spread under any climate change scenario. This study suggests that the risk of spread of the giant African snail in populated cities within central and northern China could be higher than previously expected without considering human activity. Timely effort in identification and eradication of this invasive species to prevent its spread in populated cities out of its existing distribution is needed.