Species occurrence
In the study, 2130 occurrence records of A. annua were collected for modelling its potential distribution. Most of these data were retrieved from several online databases. They were Global Biodiversity Information Facility (GBIF,http://www.gbif.org/), Tropicos Database (http://www.tropicos.org/), National Specimen Information Infrastructure (NSII,http://www.nsii.org.cn/) and Chinese Virtual Herbarium (CVH,http://www.cvh.ac.cn/). The others were acquired from field investigation. The detailed addresses of records were georeferenced by means of GPS and Google map. In order to reduce the negative effects caused by high-density collection, SDMtoolbox(Brown, 2014) was introduced to spatially rarefy the occurrence data and remove duplicate records. Each grid cell (~10 km×10 km) just kept one record. Thus, 1062 presence records remained for building models (Fig. 1).