The California Red-legged Frog, Rana draytonii

(closely related to the Northern Red-legged Frog, Rana aurora, whose range is shown in red), is endemic to small, sometimes ephemeral river systems in coastal California, as shown by the green area of this range map:

The frogs' distribution is not continuous, however. Large expanses of dry chaparral separate the small rivers that R. draytonii calls home. Here's a view of the actual habitat available to the frogs, in the form of small, coastal river running off from the mountain ranges closer to the center of the state:

The populations of Rana draytonii, although members of the same species, undergo relatively limited genetic exchange. The rivers are connected in some places, however, and there may be some degree of migration among the demes, especially those located relatively close to each other.

The demes have been separated long enough for there to have been some divergence in phenotype among them, though they are still genetically similar enough to be considered a single species. Over time, however, genetic changes that occur in the isolated demes could result in reproductive isolation between the demes: speciation.