No...this is not a stupid question, and I have wondered the same thing myself. There are some species whose geographical areas do not overlap. However, depending upon the particular distribution map that you happen to observe, certain species may overlap. The reason I have wondered about this is because there is a group of Dats which are typically referred to as "CTs" (Controversial Tigers) and nobody can nail down precisely what species they are. Today, if I go down to San Jose I will find a tank full of 1-2" Dats that appear to be a cross between an IT and a ST. In another tank, there will be 5-6 5" CTs. Such a subspecies could only have arisen by geographical isolation or cross-breeding (maybe artificial). Given the fact that entirely different species of fish have exhibited the ability to successfully mate (producing sexually viable hybrid offspring, I would not rule out cross-breeding between two different species of Dats.
