3.2 Main environmental factors affecting distribution of PWD
Table 2. Contributions of the climatic factors to the MaxEnt model.
The contribution rate of climate factors to the adaptability of PWD in China is shown in Table 2. The greater the contribution value is, the greater the influence of this variable on the existence probability of species. The climate factor with the largest contribution rate was precipitation of the wettest quarter (bio16, 45.7%), followed by max temperature of the warmest month (bio5, 27.5%), and coefficient of the variation of precipitation seasonality (bio14, 16.1%). The cumulative contribution rate was 89.3%, showing that these factors had the greatest influence on predicting the probability of PWD. The relative importance of each variable for predicting the probability of species existence was obtained based on the jackknife of regularized training gain in MaxEnt (Fig. 3). When only a single climatic factor was used, the three climatic factors that had the greatest impact on regularized training were coefficient of variation of precipitation seasonality (bio14), precipitation of the wettest quarter (bio16), and mean temperature of the driest quarter (bio9). In conclusion, the main climatic factors affecting the potential geographical distribution of PWD were temperature (max temperature of warmest month and mean temperature of driest quarter), rainfall (coefficient of variation of precipitation seasonality and precipitation of the wettest quarter). To understand the relationship between existence probability of PWD distribution and dominant environmental factors, a logistic curve suitable for only a single environmental factor (max temperature of the warmest month, mean temperature of the driest quarter, coefficient of the variation of precipitation seasonality, and precipitation of the wettest quarter) was drawn in the MaxEnt model (Fig. 4). The suitable range was the probability of existence > 0.5. The suitable range of max temperature of the warmest month was 31 - 33℃, the suitable range of mean temperature of the driest quarter was 5.1 - 20℃, the suitable range of the coefficient of variation of precipitation seasonality was 21 - 64, and the suitable range of precipitation of the wettest quarter was 450 - 950 mm.
Fig 3. Jackknife test result of climatic factors for PWD.
Fig. 4. Response curves of the main environmental variables affecting distribution of PWD.