Author contributions

Haidong Li conceived and designed the research, Yannan Xu helped to improve the hypothesis, Chengrui Liao wrote the paper, Haidong Li, Chengrui Liao and Guoping Lv carried out the field work and the analysis, Meirong Tian, Jiarong Tian, Huihui Shi and Yannan Xu contributed to the discussion, and paper revision. (All photos were photographed by Haidong Li in this article).