Where the two species are sympatric, one would expect some kind of reinforcement to help prevent hybridization. This might take the form of character displacement, leading to more distinct morphology in sympatric areas than in allopatric areas. For two species not closely related, this would be less likely since there might be more genetic differences to help prevent hybridization in an area of sympatry.
Work Step by Step
Closely related species might be likely to hybridize back into one species, or at least to waste resources by making many hybrids, in a sympatric case. This would lead to a review of reinforcement and character displacement.