species concepts

[Dr. James Adams]

DEar listers,

Brush Walsh wrote:

> Doug raises the interesting "Phylogenetic Species Concept" (PSC)
> introduced by my former colleague Mike Donoghue, who left the sunny (and
> Lepidoptera-rich) Arizona deserts for the cool and clammy confines of Harvard.  The
> problem with the PSC is that it is so open-ended, with the character(s)
> one uses to define species groups being open to the investigator. Ideally,
> one would like to have a standard set in advance of looking at a species
> group, so the investigator bias is minimal.

I think this points out precisely why there has been such difficulty 
in deciding precisely what concept of species to use.  Different 
species of different organisms maintain their distinctness by an 
incredibly vast array of different mechanisms.  What seems to apply 
so well to some seems to apply to others only with great difficulty.  
A "standard set" of characters will be impossible, since species of 
organisms vary so greatly, as just mentioned.  The biological species 
concept still works well for some groups, but certainly not very well 
for others (some plant groups, for instance run rampant over the 
BSC).  What matters to the "species" is simply that they maintain 
a certain "critical level" of genetic distinctness from other.  
(I think I just added on to the ambiguous mumbo-jumbo!)  The problem 
is determining just what enough difference is.  I agree with . . .  
oh, I've already forgotten . . . was it Mark Walker (if it wasn't, 
sorry to whomever it was) that it will *not* be single base pairs 
that will be considered enough "distinctness"; that some level of 
moderation will prevail.  As is often the case in the biological 
world, we need to avoid "bandwagoning"; different concepts apply to 
different species -- no reason to scrap one idea when it doesn't work 
for all.  This diversity is one of the things that makes biology so 
exciting for me.
 
> The plain-old biological species concept (BSC) is simply based on genetic
> exchange --- members within a group that can exchange genetic information
> are members of the same species.  

I know of plenty of examples where this is *not* the case.  Hybrid 
organisms are found in nature, but do not mean that the two parents 
are of the same species.  Not only that, but there are numbers of 
species which maintain distinctness by several means in nature 
(behaviorally, pheromonally, etc.), but if you bring the individuals 
into a laboratory setting, the normal cues breakdown and you can get 
hybrid offspring, because the two species are not *mechanically* 
isolated. 

> PS  -- neither the PSC or BSC have anything to do with collecting, or
> banning collecting, so the lifetime of this discussion will likely be short.

Actually, this is not the case either.  Naming of species/subspecies, 
etc. depends on the subjective interpretation and use of a species 
concept by the individual investigator, so whether or not certain 
species or subspecies are considered endangered/threatened, etc. 
depends wholly on our species concept.

    Sorry.  Normally I don't preach very much.  I'll step down off 
the pulpit now.

    James