More on Biogeographic memory
John R. Grehan
jrg13 at PSU.EDU
Mon Oct 8 10:50:32 CDT 2001
>If this discussion has made clear that there is indeed a distinction, even
>if it is not absolute, it has served some purpose.
Progress in panbiogeography certainly did not stop with Croizat so it stands to
reason that there will be differences.
>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.
Did I indicate otherwise? As I said, in my mind the reader is entitled to
decide what "the" major conclusion is if they want to. I do not see it as
my role to impose "the" major conclusion on anyone. If Hovenkamp feels that
the major conclusion of panbiogeography of the book is that major
biogeographical regions are the major ocean basins, he is entitled to make
that reading. In the book we did not make a formal declaration of there
being a single major conclusion as such (i.e. our major conclusion for the
book is ....). Each chapter ends with conclusions. Perhaps the first
chapter speaks for panbiogeography in general (abbreviated slightly here)
(1) Panbiogeography is a constructive approach to biogeography.
(2) It attempts to resolve the dispersal-vicariance opposition.
(3) Panbiogeography emphasizes the analysis of locality distribution data.
(4) The panbiogeographic method does not assign taxa to already defined
biogeographic elements, regions and areas of endemism.
(5) Panbiogeography can lead to novel biogeographic hypotheses.
(6) Panbiogeography reaffirms the importance of the geographical context to
understanding the history of life.
(7) In biogeography there is only location, location, location.
If I were to be asked what I thought of as "the" major conclusion of
panbiogeography, it might well be summed up by (7). Such a conclusion may
be viewed as profound or trite. So each to their own.
>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?
No it has not. I would note that the commonality in patterns for the most
part has been concerned with either geographic overlap, or biological
relationships. However, there is nothing new in finding commonality in
patterns for different groups. I have to disagree with myself on statement
about Darwinian biogeography not being able to predict biogeographic
history without some other external criterion. Of course Darwinian
biogeography does make historical predictions about centers of origin and
dispersal for example, without using external criteria - although it does
adopt external information on geological hypotheses, for example, to frame
the predictions. I am not aware of Darwinian biogeography ever making novel
predictions about geological structure however.
>McLennan. But Turner et al. are very clear: they "hoped to detect common
>patterns (...)" (p. 221).
Given that Croizat had already demonstrated comprehensively that there are
common (shared) spatial patterns in biogeography it would not be going
against the wind to have such a hope.
But then it
>forces these spatial relationships into patterns dictated by geology or
>tectonics (by assigning "baselines" in the way that it does).
"Forcing" is not a term I would have applied. The technique is simply one
of spatial correlation between spatial biological and geological patterns.
It is this spatial correlation that provides the biogeographic criterion
for hypothesizing a historical relationship by correlating a pattern
(biological) with a pattern (geological) in contrast to Darwinian
biogeography where the correlation is between a pattern of biological
relationship and a hypothesized geological history (represented as a
narrative or cladogram).
>So there is
There is independence of method with respect to constructing tracks, nodes,
and main massings. Of course a methodological connection with geology is
then proposed as otherwise there would be no criteria for hypothesizing a
particular historical association.
>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.
As the sentence states - the simplest way is to form a track is to use a
minimal spanning tree. However, to draw a track one must have some kind of
systematic (biological) hypothesis. I agree with Hovenkamp in that it would
be interesting in a future panbiogeographic book to include more examples
of track construction with details of the phylogeny also presented. This
approach is present in some of the panbiogeographic literature so anyone
more interested in this aspect can access those examples for now.
>>>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.
Given that the difference is in concept of biogeographic homology
(Croizat's being spatial, vicariance cladistics being biological) it is
not, in my mind, simply a matter of semantics.
>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
Any my view of this is that vicariance (cladistic) biogeography lacks a
spatial criterion for biogeographic relationship.
>In earlier posts I already noted that throughout the entire book,
>demonstrations of this ability of CGH Panbiogeography are virtually absent.
I agree. The book focused on spatial relationships and homologies for given
taxa. Comparisons between detailed biological relationships and spatial
relationships for specific could prove to be useful for a future book. Of
course one may also take the converse, and see vicariance (cladistics)
biogeographers incorporating spatial homologies into their analyses.
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