All Ecosystems Need Water
Top: Many animals, like polarbears, caribous, whales, and people, live in the icy Arctic. Bottom: In the dry desert, kangaroo rats get all the water they need from the food they eat.

How much water is there on an island or a mountaintop? The answer determines what lives there, and how many of them.

An ecosystem is a community of living things, or species. Some ecosystems are very wet and others very dry, some with fresh water and others with salty water. Some ecosystems, like coral reefs, support lots of species, and others, like the dry Antarctic valleys, support very few.

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