paraphyly

[pierre deleporte]

A 09:55 26/07/2002 +0200, Zdenek Skala wrote :
>zdenek:
> >>...the concept of having some measure of gap significance (S)
> >>enables to make an ordering of gaps in the lines of
> >>S(B|C)>S(D|E)>S(A|B)>...etc.
>
>pierre:
> >I simply don't think the sequence (hierarchy of gaps) is necessary for
> >cladists. It's only "gap significant or not", .. Am I
> >missing something here ?
>
>I believe so. In the concept of *any* measure ("S" in our case) is
>implicit the ordering. For example, to measure the significance of gaps by
>number of apomorphies, % of bootstrap support or whatever it is implicit
>that 5>4>3>2 etc. Hence, once you have a measure (and even cladists need
>it for this purpose), you need no extra operation to have the hierarchy of
>gaps which is also sufficient for an eclecticist. Could it solve our
>discussion?

I think that answering the following question could help solving our
discussion :
what exactly will a cladist classifier do with a hierarchy of gaps ? With a
"5 point gaps", he names a monophyletic group above the gap (the
eclecticist will add: putting a stop to a paraphyletic group below, which
is not a concern for the cladist). Now, facing a "3 points gap", the
cladist will name the monophyletic group above. Just as for a larger gap.
This time the eclecticist will name only the monophyletic group above.
So the eclecticist can take larger gaps to stop paraphyletic groups, and
smaller gaps to name monophyletric groups only.
The cladist will take all kinds of gaps for naming monophyletic groups.
What else ? If nothig else, what does the cladist cares with a hierarchy of
gaps among "significant" ones ?

I see both the cladist and the eclecticist selectin "significant gaps" for
naming taxa.
But inside this selection, the eclecticist decides which gaps (the larger
maybe) are worth naming a special kind of groups (paraphyletic groups),
when the cladist does not.

Isn't this a difference ?

Or does the cladist uses his own way "larger gaps" for some purpose, which
could be balanced with "paraphyly delineation" in eclecticism ? Which purpose ?


What does cladistics defines (besides "monophyletic groups worth naming",
and of course different from "paraphyletic groups worth delineating"), and
requiring a hierarchy of gaps ?

Pierre