common names/systematics

[Chris Durden]

>Date: Thu, 10 Jun 1999 13:08:32 -0500
>To: jadams at carpet.dalton.peachnet.edu
>From: Chris Durden <drdn at mail.utexas.edu>
>Subject: Re: common names/systematics
>In-Reply-To: <13BB9A0459C at carpet.dalton.peachnet.edu>
>
>At 10:47 AM 1999:06:10 EST5EDT, you wrote:
>
>
>
>>I would argue that species are probably rarely actually treatable as 
>>individuals.  What probably really *does* respresent  evolutionary 
>>individuals are *populations*.  I don't truly believe that a 
>>widespread species has enough gene flow so that if major climatic 
>>change takes place all populations will respond all in the same 
>>fashion, as a single unit.  It is different *populations* of a 
>>species that are potentially under different selective pressures, and 
>>only if the species is represented by one population only will the 
>>*species* respond as an individual.  If there is a very broadly 
>>dispersed population of a species, then widespread gene flow actually 
>>*resists* change within smaller subsets of that population.  At any 
>>rate, I doubt that species are truly *evolutionary* individuals in 
>>most cases.
>>
>>             James 
>>
>>Dr. James K. Adams
>>Dept. of Natural Science and Math
>>Dalton State College
>>213 N. College Drive
>>Dalton, GA  30720
>>Phone: (706)272-4427; fax: (706)272-2533
>>U of Michigan's President James Angell's 
>>  Secret of Success: "Grow antennae, not horns"
>>
>
>  That is why the greatest departure from the norm of a species is usually
found in isolated peripheral populations. That is why the population of the
species heartland holds the greatest variation around the norm including
adaptation to altitude, breadth of foodplant menu. Peripheral semi-isolates
often tend to hold less variation unless geneflow is maintained by
immigration or there is hybridization with a related lineage.
>  This applies geographically at one time, and temporally with the fossil
species acme forming a temporal heartland.
>  So what is speciation? When a peripheral isolate looses breeding touch
with the heartland, it may or may not run with selection under changing
conditions until it can no longer interbreed with other populations of the
same immediate ancestry. It steps into a new niche and becomes a new species.
>  We need the concept of subspecies, with names, in order to identify and
study the interesting peripheral populations that have diverged from the
species norm.
>  A subspecies can be geographically peripheral, seasonally peripheral, or
peripheral in any number of ecological preferences.
>  As you see, I think punctuated equilibrium theory is just great and each
equilibrium is a subspecies or species. I think Verity was appropriate in
considering multiple strengths of subspeciation, although the way he
handled it in naming has not been appreciated.
>  The flip side of this is that I have a hard time seeing a cline between
subspecies that are based on more than one character. If the difference is
one clinally changing character - the difference is not subspecific. If a
cluster of characters change over a mappable zone of co-occurrence with
intermediates, then the ends are subspecies and the intermediates are just
that.
>  In a real situation it is possible to identify different habitat
preferences of different subspecies in the zone where they meet and
interbreed. In good years all survive. In bad years the intermediates are
at a disadvantage in either habitat.
>.......Chris Durden