Now my first impression is that this is really just the biological definition of species using genetics to determine reproductive isolation, and one that would be useful for finding "cryptic" species, one that could be applied to asexual species, and even extended to some fossils (where DNA is recoverable).
I wouldn't phrase it that way, but reading purely what's in your post, it seems the same to me.
Reading further it seems that they establish a somewhat arbitrary delineation for "type" species concept based on <0.5% difference in the mitochondrial cytochrome-b gene:
The number seems arbitrary as they haven't defined what "often" means. Also seems that it's lacking any theoretical underpinning, and is pulled straight from the data with no attempt at providing additional theoretical "motivation" for choosing the number.
Thus I would define any population with a single peak frequency distribution as a species, any population with two peaks and a high "saddle" between them as incipient species, and any population with two peaks and a low "saddle" as different species. Analysis of this type of pattern for species like horses, zebras and donkeys would give you an idea of the saddle height necessary for speciation.
Razd, sorry, I didn't understand what frequency distribution you were talking about here, or in the other part of your post. Could you elaborate?
Sorry I couldn't come up with any better comments... but thanks for the information.