Climate-Driven Spatiotemporal Dynamics of Potential Distribution for Nanorana quadranus in China

Global climate change is accelerating the loss of biodiversity worldwide. The Qinling and Daba Mountains represent National Key Ecological Function Zones in China where complex environmental gradients render resident fauna sensitive to climatic fluctuations. However, the specific spatiotemporal dynamics of endemic species in this region in response to these shifts remain largely unquantified. Nanorana quadranus, a Near Threatened amphibian endemic to this region, serves as an ideal ecological indicator species due to its reliance on cold-water mountain streams and its sensitivity to thermal and hydrological fluctuations. In this study, the optimized Maxent was utilized to predict the current and future suitable habitat distribution of N. quadranus under the SSP2-4.5 and SSP5-8.5 scenarios. Additionally, the biomod2 ensemble framework was employed for independent spatial validation. By analyzing the relationship between geographic distribution and bioclimatic variables, it was revealed that the Minimum Temperature of the Coldest Month (Bio6) is the most important predictor (42.9% Percent Contribution, 75.9% Permutation Importance), suggesting a strong statistical association between Bio6 and the potential distribution of this species. Model results indicate that under current climate conditions, the total suitable habitat area reaches 39.95 × 10⁴ km², primarily distributed in the Qinling-Daba Mountains of central and southwestern China. Future projections indicate a continuous and severe contraction of suitable habitats for N. quadranus, with habitat loss substantially exceeding habitat gain. Furthermore, the centroid of suitable habitat is projected to shift northwestward by 417.3 km by the end of this century under the SSP5-8.5 scenario. The results of this study not only quantified the current and future potential suitable habitat distribution of N. quadranus, but also provided scientific measures for the conservation of this Near Threatened species.