Re: Species [arbitrary to a degree]

["Ken Kinman" <kinman@hotmail.com>]

    I do think of a ring species as a populations of genes.  In the case of 
circumpolar gulls, their physical mobility would naturally make the mobility 
of genes easier as well.
    However, if you have a "ring species" of something like a gopher (or 
other rodent that has a small individual home range), the mobility of genes 
can be greatly impaired.  As long as some gene flow continues through the 
intervening populations of the ring, I would still regard it as a single 
species.
     Once gene flow is completely impeded at some point within the ring, 
the process of speciation tends to speed up considerably, but if there is a 
potential for the "impedance" to reverse itself, there is always the 
possibility for gene flow to resume.  This demonstrates how fuzzy species 
can be at the edges (especially in the time dimension).  Whether a given 
"impedance" will cause speciation is subject to vagaries of historical 
contingencies if the situation might be reversed before it is too late.
    Luckily only a small percentage of species will give us such problems 
at a given time in evolutionary history (such as the present time), but they 
do demonstrate one of the reasons why the species problem is so difficult 
and controversial.   But the recognition of species solves more problems 
than it causes, so I am definitely not in favor of adopting a more 
simplistic phylogenetic species concept (and the thought of abandoning 
species altogether is horrifying).
            -------Ken Kinman
********************************************
> The circumpolar gulls are only a problem because of trying to use
> 'species' in a way that relates directly to morphology.  If you think of
> them as a population of genes, you can recognize that the mobility of
> the genes within the population is unimpaired for having directional
> constraints.


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