Analysis of amphibian diversity and its influencing factors in the coastal islands of southern Zhejiang

The theory of island biogeography posits that geographical features play a key regulatory role in shaping biodiversity. As a dispersal-limited group, amphibians are particularly sensitive to island effects. To clarify the community structure characteristics of amphibians on the coastal islands of southern Zhejiang and identify their influencing factors, this study analyzed survey data collected from October 2021 to July 2025. Integrating island geographic characteristics and land cover data, cluster analysis, redundancy analysis, machine learning models, and SHapley Additive exPlanations (SHAP) were employed to elucidate the driving mechanisms behind community structure. The results indicated that a total of nine amphibian species from five families and one order were recorded across 36 islands. Duttaphrynus melanostictus , Fejervarya multistriata , and Hylarana guentheri were identified as the dominant species, showing significant distribution correlations ( P < 0.05). The Shannon-Wiener index was highest on Dongtou Island, Damen Island, Lingkun Island, and Nanji Island. Cluster analysis based on community similarity using the elbow method grouped the islands into two categories. Human activities, along with the proportions of agricultural land and freshwater cover, significantly influenced the current amphibian community structure. The XGBoost model demonstrated the highest goodness of fit for diversity indices and exhibited optimal prediction stability. SHAP analysis identified land area (ARE), shape index (SAI), and distance to the nearest mainland (MID) as key driving factors: ARE had a strong positive effect on island biodiversity, whereas an increase in SAI promoted diversity on small islands. An increase in MID generally reduced diversity on small islands but enhanced it on larger islands. This study quantifies the differential regulatory mechanisms of island geographic features and provides a basis for formulating biodiversity conservation strategies for coastal islands.