Cladistics and "Eclecticism"

[Curtis Clark]

At 07:05 AM 2/7/02, Pierre Deleporte wrote:
>Now I fully agree with Curtis that, under a model of peripheral isolation
>evolution with founding effect and acceleration of evolution in the
>budding species ("saltation"), the example above could be interpreted by
>ecologists as B2 likely budding out of ancestral B = strictly identical to
>unchanged B1.
>This is a possibility. But it remains that 5 is merely "different from 6"
>at face value, and 5 = autapomorphy is also a possibility, because B1
>could have evolved a little bit. Who knows? Peripheral isolation is a
>vicariance event after all... So, where is the point for systematics?
>Indicating the possible alternatives? With markers?

Your first example, I agree, cannot be differentiated on the basis of
characters from a simple dichotomous split. I was thinking more of the
second case, and not as an absolute indicator, but rather a suggestion of
speciation in a small peripheral isolate. To those of us that study
speciation, we take whatever clues we can get.

>Should branch length information be added in the nomenclatural
>conventions? With markers?  Following which criteria?

I disagree, however, that this has anything to do with the specific
paraphyletic taxa supported by the eclectists. If Ken could show me
evidence for a single unbranched lineage between two branch points that
changed enough to separate reptiles and birds, I *might* reconsider. But my
experience of paraphyletic groups is that the separations tend to go where
we know the least about the evolution of successive key features, and Ken's
moving a bunch of the pre-winged coelurosaurs into Aves tends to confirm my
view (what happens when we find feathers on T-rex?).

Zdenek correctly points out that cladists do something similar when they
pick well-supported clades for taxa (perhaps the poorly-supported ones
simply show the same ignorance as the apparent gap between reptiles and
birds). But because our classification system is non-overlapping, accepting
Reptilia precludes accepting Archosauria *at any rank*, something that
doesn't happen with clades.

>Thanks a lot for comments. What would you do?

Phylocode. The species of hybrid origin can then be a member of both
clades. Why do you think flowering plant botanists are so prevalent among
Phylocode supporters?

For the record, if we had a formal system for naming lineage groups, I'd
worry a lot less about paraphyletic Linnaean taxa.

--
Curtis Clark                  http://www.csupomona.edu/~jcclark/
Biological Sciences Department             Voice: (909) 869-4062
California State Polytechnic University      FAX: (909) 869-4078
Pomona CA 91768-4032  USA                  jcclark at csupomona.edu