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Re: Livezey and Zusi's paper plagued with convergence?



--- David Marjanovic <david.marjanovic@gmx.at>
schrieb:

> ----- Original Message ----- 
> From: "evelyn sobielski" <koreke77@yahoo.de>
> Sent: Sunday, September 30, 2007 7:09 PM
> 
> > PS: for all that's being said, I wouldn't have
> > quantitative analyses overrule qualitative ones in
> > every case.
> 
> What exactly do you mean by "qualitative"? Or
> perhaps I should ask how is it 
> possible to measure the quality of a character?

See most Mourer-Chauviré, older Olson etc papers.
One-by-one character comparison with possible
relatives, discussion, putative systematics. As
opposed to quantifying characters into a matrix.

> > Or in shorthand:
> > - "Cnemial crest present/absent" is not advisable
> as a
> > character.
> 
> Sure it is.

OK, I was talking about birds. The cnemial crest,
morepver, is phylogenetically informative, but if you
score it thus you're asking for trouble. See also
doi:10.2307/2413412

> What is not advisable is to use too few characters,
> or correlated 
> characters.

Or characters/definitions with, all things considered,
widespread convergence (widespread numerically,
widespread phylogenetically, it makes no difference)

> > - Good taxon choice will not necessarily increase
> > robustness (and might even decrease it), but
> overall
> > reliability (as testability of hypotheses hinges
> upon
> > it)
> 
> Where's the difference?

With robustness I was referring to the tree (the
inferred character phylogeny). Reliability I consider
here a measure of how well suited the consensus trees
are to infer the actual (evolutionary) phylogeny.
I.e., how good an approximation is the tree PAUP etc
produce to the actual tree one wants to know?

> Increasing taxon sampling can lead to trouble if too
> few characters are 
> available.

That seems to be indeed the case across all types of
data. The difference is under which circumstances
"supertreeing" starts to become doable. 

Eike


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