Is it possible to create a new species from existing subspecies that already exist? For example, dogs come in a great variety of shapes and size. But if every type of dog was killed off except the Wolfhound and Chiwawa, would the 2 types be considered different species as it would be highly unlikely that the 2 would be able to mate without significant difficulty (unless artificially)? Or would something else have to happen for the 2 dog sub-types to be considered different species?
According to the Biological Species Concept, the most common current definition, species are defined by what happens in nature. Species are those natural populations which do not regularly hybridize when they are found together in nature, or which are judged to be sufficiently different that they would not do so if brought together.
When you are dealing with domesticated animals or populations created through artificial selection, all bets are off. This said, however, it would be possible to create populations through artificial selection that would behave as different species if they were present in nature.