1.5 Data analysis
1.5.1 Analysis of NTF species composition and distribution
The occurrence frequency (OF) for each species and sampling site was calculated respectively. OF (%) was calculated as: (number of specimens with NTF occurrence / total number of specimens) × 100%. Species with OF > 5% were defined as widespread species, while species with OF < 1% were defined as rare species.
Using the latitude and longitude of each site and NTF OFs, we then plotted distribution maps based on genus, species, and rare species with the raster , sf and ggplot2 packages in R version 4.02.
The mean variance ratio was used for evaluating NTF species distributions. A mean variance ratio of 1 indicated a random distribution (conforming to the Poisson’s distribution); a mean variance ratio >1 indicated a clustered distribution; a mean variance ratio <1, indicated an even distribution. The significance of these distributions was verified using a T-test.
We divided sampling areas into 9 grids using QGIS version 3.10. We selected the six grids with the largest sampling areas (grids A, B, C, D, E and F) for analysis (Figure S1 a). The watershed boundaries of Yunnan Province were extracted from a derived digital elevation model (CGIAR-CSI SRTM v4.1) at 90-meters resolution using GIS geoprocessing algorithms (Figure S1 b). We constructed upset plots using grid and watershed units with the UpSetR package in R version 4.02.
1.5.2 Genetic divergence and bigeographical distribution analysis of