According to the theory of island biogeography, which of the following is not an island ecosystem?

In island biogeography, an “island” is a habitat patch isolated from a different surrounding habitat; it does not have to be land surrounded by water. A mountain surrounded by desert, a lake surrounded by grassland, and a cave surrounded by forest can each be isolated habitat patches. The open ocean is not an island ecosystem in this sense, so the best answer is “The open ocean.”

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