The flora and fauna of the Himalayas vary with climate, rainfall, altitude, and soils. The climate ranges from tropical at the base of the mountains to permanent ice and snow at the highest elevations. The amount of yearly rainfall increases from west to east along the southern front of the range. This diversity of altitude, rainfall, and soil conditions combined with the very high snow line supports a variety of distinct plant and animal communities.[37] The extremes of high altitude (low atmospheric pressure) combined with extreme cold favor extremophile organisms.[50][41]