Results:
A total of 249,769 records of Reynoutria specimens with locality information (i.e., latitude and longitude coordinates) were downloaded from the GBIF database. These included 232,744 records for R. japonica , 11,608 records for R. sachalinensis , and 4,377 records for R. × bohemica . After geographic binning, and grid-based filtering, the European R. japonica dataset included 721 records; the European and North American R. sachalinensisdatasets included 432 and 114 records, respectively; and the European and North American R. × bohemica included 342 and 92 records, respectively. Model accuracy for the MaxEnt analyses based on the ‘area under the receiver-operator curve’ (AUC) approach (Merow et al., 2013), indicated that all models had high AUC scores (EuropeanR. japonica AUC = 0.948, European R. sachalinensis AUC = 0.966, European R. × bohemica AUC = 0.969, North AmericanR. sachalinensis AUC = 0.985, North American R. ×bohemica AUC = 0.986). In total, 10 of the 18 BioClim variables provided ≥ 10% contribution to the MaxEnt model predictions for at least one of the datasets (Table 1). In Europe, five variables contributed ≥10% to the climate suitability envelope for R. japonica , four variables contributed ≥10% to the climate suitability envelope for R. x bohemica , and three variables contributed ≥10% to the climate suitability envelope for R. sachalinensis . Two of the 18 variables, Bio 6 (min temperature of the coldest month) and Bio14 (precipitation of the driest month), were included in models for all three focal species. In North America, two variables contributed ≥10% to the climate suitability envelope forR. × bohemica , and three variables contributed ≥10% to the climate suitability envelope for R. sachalinensis . Two of the 18 BioClim variables, Bio 1 (annual mean temperature) and Bio 19 (precipitation of the coldest quarter) were present in models for both focal species.
Predictions of climate suitability estimated from the European records indicated that the source locality of the Kyushu strain had no predicted suitability based on records for all three focal knotweed species, the source locality of the Murakami strain had no-to-low predicted suitability based on records of R. japanoica and no predicted suitability for based on records of R. × bohemica orR. sachalinensis , and the source locality of the Hokkaido strain had low-to-medium predicted suitability based on records for all three target knotweed species (Figures 1-3). A presentation of predicted climate suitability based on European records across a wider portion of central and east Asia are presented in Supplemental Figures S1-S3. Predictions of climate suitability estimated from the North American records indicated that the source locality of the Kyushu strain had no-to-low predicted suitability based on records for R. xbohemica and no predicted suitability based on records forR. sachalinensis , the source locality of the Murakami strain had medium-to-high predicted suitability based on records for both R.× bohemica and R. sachalinensis , and the source locality of the Hokkaido strain had medium-to-high predicted suitability based on records for R. sachalinensis and low-to-medium predicted suitability based on records for R. × bohemica (Figures 4 and 5). A presentation of predicted climate suitability based on North American records across a wider portion of central and east Asia are presented in Supplemental Figures S4 and S5.