How do species concepts deal with the inclusion/exclusion of natural hybrids?
In his last post, Greig mentions his concept of species as My taxonomic unit is probably the "Biological Species": which can be defined as "natural populations of living, reproducing, genetically related individuals isolated from other populations by barriers to gene exchange". How does this concept of species explain natural hybrids? By this definition, as they do not have barriers to gene exchange (at least not total barriers), would the parent species not then be considered the same species? How would this deal with Phalaenopsis x intermedia? As the natural hybrid between P. aphrodite and P. equestris, it has, according to Christenson, also "formed a genetically stabilized population which acts like a species and is self-reproducing in nature." I guess here we are seeing the establishment of an individual species in the future, but how to deal with this in terms of Greig's definition of species? Or we could consider P. x leucorrhoda, the natural hybrid of P. aphrodite and P. schilleriana. This has not established itself as a breeding population, only isolated plants. This definition could also ask us to consider Cattleya x guatemalensis, the hybrid of C. skinneri and C. aurantiaca, as all one species. I think I would have to take the definition of species beyond this "Biological Species" and more to the direction of Greig's interpretation of Peter's: "Morphological Species": defined as "the smallest population structurally distinct and distinguishable from all others". But then I find that this can create too much splitting off of species for the smallest variations which could be found. Thanks for the discussion. Jay Norris Ravenvision Photographic www.ravenvision.ca
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