David Wright wrote:

> 2) I want to emphasize that I am *not* arguing against using
> *reproductive isolation*, which is the conceptual core of the
> BSC, as a basis for a species concept.

It sounds like we are not far apart then. However, reproductive
isolation is just the other side of the coin from lack of reproductive
isolation which is manifested by hybridization.

> My argument is with
> the operational criteria classically used to lump
> phenotypically distinct populations into single species:
> hybridization and "potential interbreeding."

One needs to carefully distinguish between the type of hybridization to
diagnose species. See Short (Auk 86:84-105, 1969) for a useful discussion
of taxonomic aspects of avian hybridization. I don't know of anybody
advocating the existence of hybridization alone as the only criterion for
lumping distinct populations.

As for the "potential interbreeding," this comes to the fore in
allopatric "semispecies" and here I agree that there is a big problem.
As I mentioned earlier, these geographic isolates, whether species or
subspecies are in fact units of evolution and thus are functionally de
facto biological species.

This problem seems to me to be a serious defect in the subspecies concept
rather than one of the species concept. Subspecies are fuzzy categories
and I would like to see the concept made more rigorous using techniques
advocated to diagnose "species" via the PSC. I have no argument with
these techniques; my whole argument is against abandoning the BSC in
favor of a PSC which ignores the forces which contribute to diversity.

----------
Joe Morlan
Albany, CA
jmorlan at slip.net