More on Biogeographic memory

John R. Grehan jrg13 at PSU.EDU
Fri Oct 5 17:23:23 CDT 2001


After the terrorist attacks arcane discussions on the minutiae of
systematics and biogeography seem to pale into insignificance. I almost
find myself wondering why
should I bother, but then that is the underlying purpose of terrorism. So I
now find myself
of a mind to continue, although the events only reinforce in my mind that
no matter how much and in what way I might disagree with my colleagues, we
all do indeed share a concept of civil conduct.

Regarding some comments from Hovenkamp


>Croizat correlated biological patterns to each other first, and only then
>to geological features. Craw et al. correlate biological patterns to
>geological features first, and then to each other.
>To me, that is a big difference.

I was not aware of such a distinction. Perhaps this may indeed be something
different.
I do know that Croizat did make correlations of individual distributions
with tectonics as well
as standard tracks so the difference is not absolute. Further, there are
post-Croizat panbiogeographic studies where standard tracks are constructed
first and then correlated with geological features. So again, it doesn't
seem to represent an absolute difference.

>In Craw et al.'s approach, it seems much
>more difficult to arrive at general conclusions (about common geological or
>geographical causes) that are not already implied in the premises.



>Their major conclusion seems to be that the "major biogeographical regions
>are (...) the modern ocean basins.". I think that proves my point.

I guess what one might decide is out major conclusion is something the reader
is free to decide.



>>>>In what way is Croizat's approach being 'integrated' with phylogenetic data
>>>>by vicariance biogeographer - particularly as vicariance biogeography seems
>>>>to simply be a version of Darwinian biogeography in that it cannot predict
>>>>biogeographic history without some kind of external (non-biological)
>>>>criterion. Usually this criterion is concordance with some hypothetical
>>>>historical sequence from geology or paleogeography - and in this respect is
>>>>no different from traditional Darwinian biogeography.
>>>
>>>A fairly limited view of the developments in vicariance biogeography. Even
>>>from reading Turner et al. it should be clear that there's more to it than
>>>that.

In what way?


>>>I'm not going to argue whether vicariance biogeography has reached its
>>>goal or not, but at least this line of approach tries to do two things
>>>that Craw, Grehan and Heads' Panbiogeographys seems to have given up on:
>>
>>
>>>1. It considers biological evidence independently from geological data
>>>(treading in Croizat's steps)

In panbiogeography the track method is explicitly constructed using phylogeny
to order the localities to be connected by minimal spanning links, so
biological 'evidence' is used. The difference is that localities are given
spatial relationships where the sole use of biological relationships does
not provide information on spatial relationships.

>One would have to check the literature from the '70's to find out in how
>far vicariance biogeography actually derived from or was inspired by
>Croizat. My statement is based on rereading Hull (1988).

There is an important distinction I believe between derivation and
inspiration. I would
agree that Croizat may have inspired vicariance biogeography, but
derivation is not substantiated.


>>>2. It tries to incorporate the extra detail that resolved phylogenies
>>>provide, especially with regard to the historical component (an expansion
>>>of Croizat's method, which has no way to deal with historical information
>>>of this kind).

Panbiogeography can incorporate as much detail that resolved (biological)
phylogenies provide in track construction. The more detailed the phylogeny
the better for panbiogeographic analysis as far as I am concerned.


>But then again, it may be my imperfect understanding of the subtleties of
>the English language, that prevents me from reading these statements as
>simple expressions of well-meaning criticism.

Croizat never minced words and I would agree that they were harsh.  Whether
they were appropriate or not will be up to individuals to decided.
Personally I did not agree with him on at least some, but in my case this
was not a hurdle to reading his works. I agree that for others this would
not be the case.

John Grehan

Frost Entomological Museum
Pennsylvania State University
Department of Entomology
501 ASI Building
University Park, PA 16802. USA.

Phone: (814) 863-2865
Fax: (814) 865-3048

Frost Museum
http://www.ento.psu.edu/home/Frost/index.html




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