More on Biogeographic memory

Pierre Deleporte Pierre.Deleporte at UNIV-RENNES1.FR
Thu Oct 18 15:47:17 CDT 2001


A further comment about "synapomorphy" in Panbiogeography:

At 15:12 16/10/2001 -0400, John Grehan wrote:

>>(Peter Hovenkamp:) Perhaps the confusion is in the use of the word
>>"synapomorphy"? To me, the use of the word synapomorphy suggests going
>>all the way from primary homology assessment via phylogeny reconstruction
>>to recognizing synapomorphies on the preferred tree. I realize that with
>>a more restrictive view of synapomorphy ("derived similarity") the whole
>>discussion may seem to be pointless...
>
>(John Grehan:) I have not delved deeply into the
>philosophical/methodological issues of synapomorphy in biogeography and
>systematics so I cannot offer more than my current understanding of the
>baseline as a synapomorphic character for tracks. I would agree that its a
>subject that could warrant further
>evaluation and investigation by those so interested.

Apomorphy is a notion relative to plesiomorphy, two states of a same
character in a relation of polarity.
May I suggest that synapomorphy requires a rooted tree, in order that a
notion of "derived" character state makes sense, and thus synapomorphic
taxa sharing a derived character state makes sense.
It seems that the unrooted minimal spanning trees used in Panbiogeography
cannot fit a notion of "geographical synapomorphy": no rooting, no polarity.
If a baseline is a repeated pattern observed in different tracks, then the
term "redundant" could describe this fact: geographical (or spatial)
redundancy, geographical similarity... with no notion of polarity implied.
Similarity is not "derivation" in itself, the latter notion requires an
additional  "derivation rule" to polarize interrelated similarities.


And for Peter:

At 12:36 18/10/2001 +0200, Peter Hovenkamp:

>I'm beginning to have some difficulties keeping up a three-cornered
>conversation in this way (not meaning I don't enjoy the exchange of
>opinions. I think we are beginning to understand one another).

Sorry, for I feel partly responsible of the trouble. Certainly we have made
some progress in mutual understanding (if not agreement).

>So just a few remarks while I sort out a more coherent reaction on the
>criticisms about "Pattern biogeography" which I find myself
>(understandably) accused of...

As far as I understand the different approaches, I would rather address the
qualification (but surely not "accusation"!) of "pattern biogeography" to
part of Panbiogeography, when it seems that a spatial minimal spanning tree
for one taxon can be presented without an obvious historical explanatory
theory (thus why should we do that, what does it mean?).

I view Peter Hovenkamp's approach a quite different way (explicit use of
the temporal hierarchy of clades / spatial distributions of sister groups),
but I just could not let pass the notion of "patterns speaking for
themselves" without comment, because out of an explicit context this sounds
exactly like a purely "pattern" approach with all the arbitrariness
involved (or illusion of virginal observation of a self-evident objective
truth).


Pierre




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