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Posted by Rick Staub on January 12, 1999 at 15:51:52:
In Reply to: Re: Species is only Taxonomic level that is "real" posted by Troy H. on January 11, 1999 at 09:15:41:
I think another problem with the biological species concept is how do you define interbreeding. Is this 2 populations breeding in a cage (completely unnatural) or in the wild. I would have to say that many snake species would breed with each other in a cage, but never in the wild even when there populations overlap (L getula and E guttatta). There are always contradictions also. The west coast ensantina salamander is a good example since it has a number of interbreeding populations around the north end of the Central Valley, but where the two sides cross over in So Calif, they do not interbreed. Are they a separate species? It is one continuous population with defined integrade zones so probably one species.
The problem with recreating evolution is that you have to make assumptions. The fewer assumptions you make the more objective and hopefully more true your representation. The evolutionary species concept tries not to predict the future (whether 2 allopatric populations will overlap in the future). The biological species concept (as noted above) also assumes that whether 2 species can breed is the most important criteria for determining species. Maybe, but maybe not. Assumptions do have to be made and there is no perfect study or criteria.
Something that was left out (or probably just considered a given) of the evolutionary species concept is that the two populations have to be distinguishable. This is where it gets tricky especially when regarding elevating some current allopatric subspecies (L. zonata, L. pyromelana and others as proposed once by J. Collins) to the species level. When do you consider allopatric populations distinguishable and is DNA enough even when morphologically the are identical or overlapping. Grismer found that disjunct tree frog populations in Baja could be distinguished by DNA but were unidentifiable using morphological characters. He chose to leave them as one species and just said they each have there own evolutionary coarses. No boats rocked. By the evolutionary species concept he could have made each population a species. Rick Staub
:
: In your example (if two pops diverge for a time, but then reconnect and their distinctness is swamped by panmictic gene flow between the formerly separate populations), then by the Evolutionary species Concept, the two were never separate species.
: However, the problem in applying species CONCEPTS to real world situations is that we are only looking at a slice of evolutionary time, and that we have to make our best educated guess, particularly concerning allopatric populations of animals such as snakes and small mammals that don't disperse easily (i.e. allopatry in birds is a different story than allopatry in herps).
: Allopatry is, always has been, and always will be the toughest test of any species concept. You see, we simply cannot know the future . . . will zonata & pyro reconnect 10,000 years in the future? We just can't know, so we must do our best to interpret their "species-ness" in light of our concept of species.
: Many "old-school" folks would avoid the problem of allopatry by saying that if the two pops can interbreed and produce fertile offspring, then the two are the same species . . . however, this test is in all actuality a poor measure of a species evolutionary distinctness from its close relatives . . . you see, the ability to interbreed & produce fertile offspring is by its defintion a primitive characteristic common to all the species derived from a common ancestor . . . a species must develop reproductive isolation. In many cases (e.g. leopard frogs) the two species in a group that share reproductive capability are the two most distantly related evolutionarily.
: Troy
