[Taxacom] barcode of life: PS

Stephen Thorpe stephen_thorpe at yahoo.co.nz
Sun Jul 4 20:23:01 CDT 2010


Interesting...

>Of course, we don't know for sure -- because as far as I know, nobody has done the experiment.

>But what we REALLY don't know, and likely will not know for a long time, is whether the reason the bulk populations are so consistently different is the result of some sort of selection pressure keeping them that way, or is a result of dynamic propensity to disperse over appropriate time scales (i.e., the hybrid zones are so narrow only because they came into existence only relatively recently).

Hearing you loud and clear! I agree on both points! I would go further and say that we never (or hardly ever) no for sure if two forms are the same species or not, and we have to move on despite the uncertainty. Many (putatively) new species of insect are described still from a single specimen. How can we know? It isn't about knowing, but about making sensible judgement calls, but not based so much on "communicative needs", but more on experience of uncontroversial species distinctions in the group (e.g., well it's as different as these other related species are to each other, and no species is known to vary to THAT extent...)

I don't know why you perceive the "fuzzy zone" to be so much wider than I do (and increasingly so). In groups that I know, I just see the same old species turning up over and over again in samples, and they are almost always distinct enough from each other to be confident of having one species or two. The world is certainly NOT one in which every species grades imperceptibly into every other species, though it might have been that way. Similarly, species taxonomy as we know it would also be impossible if every species were parthenogenetic (the few that are so represent "problem cases") . Then species boundaries would be just like generic boundaries - i.e., purely subjective/arbitrary. There would be no basis whatsoever for deciding if two very similar allopatric populations were the same species or not. Probably, in that case, a morphological (and/or molecular) species concept would be appropriate. Two allopatric populations which differed ONLY in
 that, for example, the individuals in one were just perceptibly darker in colour than individuals in another would be distinct species. Intrapopulational variation would be a big problem, though there would be less of it without the sexual reproduction. Perhaps "communicative needs" would then play a bigger role?

If our views differ in any substance, it is that I don't think taxonomists are merely "guided" by the BSC, rather I see the BSC as more definitive of what we mean by "species" (which explains why taxonomists are guided by it - otherwise where is the connection of relevance?). The concept of "species" doesn't fit the world's biota perfectly, but it does so really very well, despite a few problem cases. We appear to be disagreeing on how well? And I don't think the lack of certainty about species distinctions is a problem ...

Stephen

 

________________________________
From: Richard Pyle <deepreef at bishopmuseum.org>
To: Stephen Thorpe <stephen_thorpe at yahoo.co.nz>; Richard Zander <Richard.Zander at mobot.org>; taxacom at mailman.nhm.ku.edu
Sent: Mon, 5 July, 2010 12:36:53 PM
Subject: RE: [Taxacom] barcode of life: PS


I said: 
> > So, by anyone's metric, there are effectively no 
> > biological reproductive barriers between these 
> > two species [C. flavissima / C. vroliki ]

You said:
> Incorrect!

I think we differ in our meaning of the word "biological" in this case.
When I used it in the line above, I meant "intrinsic to the biology of the
organism".  I would wager a lot of money that I could take any two
individuals of the two speies from anywhere within their respective ranges,
and they would be just as likely to produce viable offspring as any two
individuals from an established hybrid zone.

Of course, we don't know for sure -- because as far as I know, nobody has
done the experiment.

But what we REALLY don't know, and likely will not know for a long time, is
whether the reason the bulk populations are so consistently different is the
result of some sort of selection pressure keeping them that way, or is a
result of dynamic propensity to disperse over appropriate time scales (i.e.,
the hybrid zones are so narrow only because they came into existence only
relatively recently).

> It is all about finding (describing) patterns in nature - 
> patterns which "really are out there" (and need not have been if things
were different)
    
I've never, ever claimed that there are no patterns in nature.  If there
were no patterns, there would be nothing for taxonomists to do.  My only
contention is that evolution does not consistently produce sets of organims
that fit nicely into boxes we like to call "species" (by any definition of a
"species", BSC or otherwise).  The argument is about the degree of
inconsistency (which, following your human-height example, essentially
translates into the shape of the bell-curve). 

As I said in my last post, my own view of the shape of the average
bell-curve between species has gradually become broader (=less distinct)
over the years, as I accumulate more observations of natural populations.

Aloha,
Rich


      


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