I'm currently working on a world where there are two groups of dragons, Continent dragons and island dragons. The basic story is that long ago there was one massive population of dragons that lived on the continent, before some kind of natural disaster or predator forced some of the dragons to flee to an island far out in the ocean.
The continent dragons evolved into three main subspecies, which all appear slightly similar, while the island dragons evolved into eight main subspecies that are each highly specialized to the environments they live in, and all look very different. The island dragons lay smaller nests and grow larger and slower than continent dragons. The continent dragons are more intelligent and civilized than the island dragons.
My question is, why would a smaller population be more specialized to their environment than a large population that reproduces faster?