More on Biogeographic memory
Hovenkamp at NHN.LEIDENUNIV.NL
Tue Oct 16 10:33:36 CDT 2001
At 08:35 AM 10/12/01 -0400, John Grehan wrote:
>>So my question still stands: character analysis is about character states
>>and character state trees, and why is the equivalent in biogeography not
>>about taxa and taxon trees?
>>(I wish I could think of a proper equivalent in character analysis of the
>>CGH Panbiogeographic concept of spatial synapomorphy - perhaps after the
>On this I guess we take different interpretations. At present I stay with
>the view that form systematics includes designation of informative
>characters by synapomorphy and it is designation of a biogeographic
>synapmorphy to which Craw was referring. While I believe I am correct in
>this understanding, I do not understand Hovenkamp's view that the
>biogeographic 'equivalent' of character analysis in form systematics is
>'taxa and taxon trees' since that is not an equivalent of form systematics,
>that is form systematics itself.
From Craw's statement (but also from many of John Grehan's) I understand
that Panbiogeography uses an "equivalent" of character analysis in form
systematics. So I was looking for an operation that would be subsumed under
Panb just as character analysis is subsumed under form systematics. That
such an operation would in fact be form systematics itself is an
interesting result, which cannot be simply discarded just because it is
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...
>>Of course. But to be examples of the same common pattern they have to
>>comply with *both* requirements. The ratites and Nothofagus don't.
>If one is referring to 'same common pattern' as a common baseline the
>answer would be no as there can be two different distributions that do not
>overlap at all and share a common baseline since both tracks cross the same
I think we are basically in agreement here, but somehow got lost in the
argument. So I'll stop it.
>>So it seems to be a matter of the level of detail of the analysis. In a
>>more detailed analysis of the Indian Ocean basin, CGH Panbiogeography may
>>consider different baselines across different parts of it?
>>If that is so, it raises the question on what grounds CGH Panbiogeography
>>is able to decide in advance of the analysis that there is a part-whole
>>relationship between these different parts and the whole Indian Ocean?
>>After all - that is not trivial. An alternative would be that there is a
>>part-whole relationship between the southern half of the Indian Ocean and
>>the "Southern Basin". In which case the designation of the
>>Madagascar-Australia track as Indian Ocean baseline should be changed.
>>Somehow, for some reason, CGH Panbiogeography has already opted for the
>>first option, but has it seriously considered the alternative? If so, on
>>what grounds has it been rejected?
>There is always the possibility that there may be disagreement about the
>designation of baselines, but to do so one would have to accept the
>validity of baseline homology otherwise the question is pointless (for
>example I would not bother to decide among two competing Darwinian center
>of origin hypotheses).
So in order to disagree with you I'll have to agree first...
>If one decided to critique and offer alternative
>baseline designations that is fine with me - I would naturally encourage
>the activity. Certainly there are examples of more detailed considerations
>of baselines such as Craw's (1989) comparison of baselines with respect to
>the Chatham Islands.
>Designation of different trans-Ocean baselines is certainly a possibility.
>I would conceive, for example, the designation of distinct tectonic
>features within an ocean basin providing different terms of spatial reference.
>On the face of the evidence a Madagascar-Australia baseline is simply
>referring to the distribution crossing the Indian Ocean.
The basic point of disagreement remains. I would like to let the patterns
we observe speak for themselves. Opposed to that, we find John Grehan, who
claims that knowledge about tectonic features should be used to decide
exactly which patterns can be compared and which had better not; and Pierre
Deleporte (bien étonnés de se trouver ensemble...), who claims that
knowledge of ecology should be used in the same way.
To both I say: if either tectonics or ecology is really important, you will
be able to find traces of it in the result of the analysis.
To John Grehan: If the Indian Ocean is one tectonic feature, you can expect
to find the a single consistent pattern - if it is not, you may find
different general patterns involving the northern and the southern part...
To Pierre: The way across a mountain range may not be the "shortest" way to
connect two groups of fish - but if it repeatedly turns up between
different pairs of sister-groups of fishes - then maybe the mountain is a
relevant feature after all...
>>Whoopee again. I totally agree that explanation of individual taxon
>>distributions should be based on all relevant evidence.
>Except spatial evidence through baseline homology apparently does not
>constitute evidence at all in your view.
(if only I knew exactly what it was...)
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hovenkamp at nhn.leidenuniv.nl
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