How are communities of plants and animals organized in nature? This is a challenging question, because there are too many species in most communities to study this problem experimentally. For example, even with only three species (A, B, and C), eight different "communities" or distinct species combinations can be formed, based on the presence or absence of each species in the community: 0, A, B, C, AB, BC, AC, and ABC. With S species, 2~s possible species combinations can be formed, which is far too many for a wieldy experiment.
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