Why is this so? Why should diversity drop off with isolation? For some species, the answer seems pretty straightforward: the slice of the habitat they’ve been marooned on is inadequate. A big cat that requires a range of a hundred square kilometres isn’t likely to make it for long in an area of only fifty square kilometres. A tiny frog that lays its eggs in a pond and feeds on a hillside needs both a pond and a hillside to survive.
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