They can survive because over time their species have evolved to withstand the climates in the mountains
Because they are suited to live in a certain environment that is or similar to a mountain. They might be suited to the moisture, climate or rainfall of a mountain.
Seeing as I have lived in the mountains my whole life, I know that trees other than the evergreens, the deciduous trees lose their leaves in the fall. As do bushes and flower plants. As for animals, bears, squirrels, chipmunks, raccoons, to name a few, go into hibernation. Animals such as deer and birds migrate to warmer places and come back in the spring when the weather gets warm again. I hope this helps