Platnick's view of Phylocode

[Pierre Deleporte]

At 09:21 12/03/2002 +0100, Zdenek Skala wrote:
>All questions you are asking were raised and answered in a recent thread 
>on paraphyly. You need not accept the logic of "eclecticists" but you will 
>learn more by reading the mail archives than by asking the same questions 
>again.

Possibly, so let's apply this to everybody, for instance ;-) :

>-----Original Message-----
>From: Thomas Pape [mailto:thomas.pape at NRM.SE]
>
>#3
> >Why cannot a 'minor gap' be just as scientifically exciting as a 'major
> >gap'?
>Z. Skala:  Minor gaps can receive lower ranking in the system while the 
>major gaps receive higher ranking - quite similarly to the hierarchy of 
>small/large clade hierarchy in the holophyletic system.

It seemed to me that a common agreement had been reached concerning the 
fact that a "significant" or "relevant" gap or novelty could be either 
quantitative or qualitative and depend one one's interest. We can avoid 
chewing this same question again and again.
There seemed also to be large agreement that the notion of "significant 
gaps" was involved in eclectic as well as in (incomplete) cladistic naming.

I think that a real lasting debate concerns the possible "added 
arbitrariness" linked to the definition of paraphyletic groups, in addition 
to monophyletic ones (complete clades), all things beeing equal concerning 
"significant gaps".
Or in other words, possibly viewing the delineation of paraphyletic groups 
as requiring additional criteria relatively to the unique definition of 
monophyletic ones.
It seems to me that deciding when a paraphyletic group "should stop" is an 
additional decision relatively to the definition of clades. And an 
additional decision logically requires additional criteria.
More precisely: we must decide when does a "gap" will be sufficient to 
terminate a paraphyletic taxon worth being named, and not only to begin a 
monophyletic one worth being named.


A side (but in my view related) question concerns the hierarchy of groups 
in an eclectic classification:

"vertebrates" include birds
"reptiles" exclude birds

Thus not only the current eclecticist must decide "when reptiles stop", but 
he has also to decide that this significant gap is not significant when 
considering "vertebrates" as a whole. Maybe feathers are getting more and 
more important the closer you look at them when climbing the tree of 
life... But I can't help viewing this as logically requiring additional 
criteria and general rules for combing them.

So, isn't there some inconsistency in the way eclecticists apply their own 
criteria? Why shouldn't vertebrates exclude birds because of the 
significant gap called "feathers"?

Birds are vertebrates are reptiles seems more coherent to me, and I think 
that this is because one applies one criterion throughout (monophyly, 
indicated by synapomorphy). Possibly being "more natural" is another point.
If internal coherence is an issue at all... For me it seems at least 
relevant to the possibility of reaching common agreement between scientists.


Also relevant to our recent debates on this list is the point by Platnick 
about considering species (diagnosable) as different from clades at higher 
levels (obligatorily defined by synapomorphies), and the development of the 
very "budding species" example we recently discussed on this list. Platnick 
suggests that, to be useful to biologists interested in evolutionary 
processes, classification should not discard some possible modes of 
speciation, and that a "species (population?) remaining the same" with a 
side budding is worth being indentified as such. Isn't this a form of 
eclecticism after all? But it does not interfere with higher levels oin the 
classification, and concerns only the terminal units.

For Ken: I'd like that you label paraphyletic groups as such in your system 
(rather than labeeling only "excluded monophyletic groups"). The fact that 
you use a conventional "family" terminal for naming both paraphyletic and 
monophyletic groups without warning seems potentially confusing, don't you 
think so?
As for Kinman codes and avoiding a "cornucopia of ranks", Platnick 
(referring to Papavero et al. 2001) suggests a very similar system: 
signalling ranks "+1", +2", or "-1", "-2" above or under a given rank.

best and cheers
Pierre



Pierre Deleporte
CNRS UMR 6552 - Station Biologique de Paimpont
F-35380 Paimpont   FRANCE
Téléphone : 02 99 61 81 66
Télécopie : 02 99 61 81 88