Answer
Hybrid zones are where two different species have overlapping ranges, allowing mating. Here is where different types of isolation, especially when incomplete, can bee seen in action and the progress of speciation followed.
Work Step by Step
Review Fig. 24.12 and the associated text. Hybrid zones may see some mating and reproduction, leading to hybrids, but the success may be low, as it may be for reproduction by hybrids. This allows speciation mechanisms to be studied in the field.