Microevolution leads to macroevolution. The reason that the salamanders at the ends which cannot interbreed are not considered a different species is because each subspecies can breed with the neighboring subspecies. But, by the time the ends of the ring meet they can no longer interbreed - they've
evolved apart. If you got rid of the transitional populations in between, you'd officially have different species.
Another example is the Greenish Warbler:
