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Distribution of populations across climatic gradients in the western United States. Maps depict (a) PC1, which describes mean annual and seasonal temperatures (higher values are warmer), (b) PC2, which describes mean precipitation (higher values are wetter), and (c) PC3, which describes seasonality of both precipitation and temperature; higher numbers denote warmer, wetter winters, and cooler, drier summers; lower number denote cooler, drier winters, and warmer, wetter summers
