Climate, more than any other single factor, determines the distribution of life on earth. Climatic boundaries establish the limits which organisms can survive. Plants, even more than animals, must be well adapted to climate in order to survive. They cannot move about or take shelter but must be equipped to endure whatever weather conditions are likely to occur. In the harsh conditions of the tundra, for example, low growing mosses, lichens, and a few flowering plants all hug the ground for shelter from icy winds.
Animals, despite their ability to move about and find shelter, are just as much influenced by climate as plants are. Creatures such as the camel and the penguin are so highly specialized that they have an extremely limited distribution. Others, such as bears are flexible enough to adapt to a broad range of climates. Oceandwelling organisms are just as sensitive to climatic changes—in this case temperature and salinity—as land animals
A. to avoid being eaten by arctic animals
B. because fertilizer is not readily available
C. to minimize exposure to the cold
D. because unfrozen water supplies are very scarce
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