Reproductive isolation evolves without geographical isolation.
A group of animals may become isolated within the range of a parent population if genetic factors cause them to become fixed on resources not used by the parent population as a whole. A particular species of wasp pollinates each species of figs. The wasps mate and lay their eggs in the figs. A genetic change causing wasps to select a different fig species would segregate mating individuals of the new phenotype from the parental population. Divergence could then occur after such an isolation.