More on Biogeographic memory

P.Hovenkamp Hovenkamp at NHN.LEIDENUNIV.NL
Mon Oct 8 10:46:12 CDT 2001


At 05:23 PM 10/5/01 -0400, John Grehan wrote:
>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.

I totally agree.

So we continue ...

>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.

If this discussion has made clear that there is indeed a distinction, even
if it is not absolute, it has served some purpose.

>>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.

I would have thought that an author of a book would have some idea about
what is the major conclusion - but then, I have no first-hand experience.

>>>>>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?

Is it really possible that it has escaped your attention that a a lot of
work in historical biogeography is concerned simply with finding
commonality in patterns for different groups? Or is it that we read
different goals in these efforts? I must admit that often such work is not
very explicit (and sometimes downright confused) about its ultimate goals -
following the confused presentation in the well-known book by Brooks &
McLennan. But Turner et al. are very clear: they "hoped to detect common
patterns (...)" (p. 221).

>>>>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.

There is no dispute that panbiogeography (and also Craw-Grehan-Heads
Panbiogeography) uses biological evidence. And I share the concern that
much of what passes for vicariance biogeography can be carried out and
presented without ever looking at a map - at the spatial relationships that
link localities or connect distribution areas. In fact - I think my
disappointment with CGH Panbiogeography is partly due to the high
expectations it raised with me by its insistence on using maps. But then it
forces these spatial relationships into patterns dictated by geology or
tectonics (by assigning "baselines" in the way that it does). So there is
*no* independence.
And I do not understand the remark that the track method is explicitly
constructed using phylogeny. "A track is a line drawn on a map that
connects the different localities pr distribution areas of a particular
taxon or group of taxa. The simplest way to construct such a graph is to
form a minimal spanning tree" (p. 20). Not a word about phylogeny there.

>>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.

I agree with the semantics - that is why I suggested that a literature
study would be necessary to decide whether "derived from" or "inspired by"
is the best term to apply.

But the point I was trying to make still stands: that Croizat's main
purpose, to establish biogeography as an independent (independent from
geology) science, is better served by vicariance biogeography than by CGH
Panbiogeography.

>>>>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.

In earlier posts I already noted that throughout the entire book,
demonstrations of this ability of CGH Panbiogeography are virtually absent.
What's more, in the entire book there is no explanation of how the
incorporation of phylogenetic detail might be achieved.
Tracks display no detailed phylogenetic information...
Nodes display no detailed phylogenetic information...
Main massings display no detailed phylogenetic information...
Baselines display no detailed phylogenetic information...
And if there is more to the CGH Panbiogeographic method, it is not listed
under the heading "Panbiogeographic Method" (section 1.3). So either it's
not there, or C G & H did not think it was an important element of the method.

>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.

A good question for everyone to consider: do such words fit into a "concept
of civil conduct"?




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