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).