High amphibian diversity related to unexpected environmental values in a biogeographic transitional area in north-western Mexico

Amphibian diversity and distribution patterns in Sinaloa state (north-western Mexico) were assessed from the Global Amphibian Assessment database (GAA-2010). A geographic information system (GIS) was used to evaluate diversity based on distribution maps of 41 species, associated with environmental data. The highest α and γ-diversities were identified in the south-eastern portion of the state, in mountain zones with a warm sub-humid climate, whereas the greatest β-diversity (multiplicative formulation) was aggregated in patches in the western portion of the state in mountains with temperate climates. A cluster analysis and Mantel test showed a strong association of Sorensen’s dissimilarity (additive formulation of β-diversity) with climate and soil moisture categories rather than physiographic categories. Additionally, the partition of Sorensen´s dissimilarity into its components (turnover and nestedness) showed a gradient of species turnover related to contrasting climate units and a marked pattern of nestedness between the middle mountains and the coastal plain. The results of the study suggest that the highest α and β-diversity values occur in the middle-humidity range as well in the transitional-climate categories. This pattern is unusual for amphibian distributions because the highest global and regional amphibian diversities are typically related to high humidity values and climate stability (warm and wet most of the year). This particular pattern, occurring in a transitional area, encourages further biological and ecological studies to clarify the status of amphibian populations and support conservation measures.