In Death Valley, California, there are several ponds that are formed in various areas of the desert. Each pond contains its own species of fish unique to the pond it lives in.

The ponds are separate habitats, so fish populations in different ponds are geographically isolated and cannot readily interbreed. Over time, this separation can lead each population to develop into a distinct species. Geographic isolation means populations are separated by a physical barrier or distance; the other choices refer to differences in body structures, behavior, or breeding times.

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