More on Biogeographic memory
John R. Grehan
jrg13 at PSU.EDU
Tue Oct 9 12:26:57 CDT 2001
At 04:14 PM 10/9/01 +0200, you wrote:
>I am afraid much of this discussion is now starting to run in circles. For
>once, I'll start deleting parts of the message while replying to other parts.
I agree. Its hard to keep track of all the issues so I will probably end up
contradicting myself if I haven't already!
>This discussion started with a statement by me that Vicariance biogeography
>at least *tried* to consider biogeography as independent from geology. What
>most, if not all applications currently *do* is another thing.
>There is not necessarily a concept of homology in vicariance biogeography.
>The application of the term "homology" to matters biogeographical is purely
>restricted to CGH Panbiogeography.
ok. In which case there is no necessary biogeographic relationship to be
derived from a biological analysis of relationships. Craw (1988) made the
following observation: "Approaches to biogeography based on attempts to
demonstrate distributional congruence are purely descriptive narrative
approaches whether in the form presented above or bolstered by cladistic
analysis of the taxa. They are not examples of analytical biogeography
because geographic distribution is taken as read and not subjected to the
equivalent of character analysis in form systematics to determine what
aspects of geographic distributions of taxa are homologies.
>Accepting this usage, then, in vicariance biogeography we can observe
>commonality when distributions (partly) overlap, in CGH Panbiogeography
>when they overlap _and_ share the same baseline. Is that it?
No. Distributions share the same baseline when their tracks cross the same
>>>he criticism is invalid. It may be John Grehan's view that
>>>explaining the distributions of individual taxa is not a useful enterprise
>>No it is not.
>Not your opinion, or not a useful enterprise?
Not my opinion
>>>It would also run counter to the general trend in the CGH
>>>Panbiogeography-book, where most examples (and many of Croizat's examples
>>>also) are concerned not with finding common patterns (generalized tracks)
>>>but with explaining single distribution patterns.
>>So panbigoeography can accomodate both "earth history" and "taxon history"
>>in Hovenkamps dichotomy.
>Failing a method to assess commonality independently from geology, just
>"taxon history", I'm afraid.
As clarified before - the independence of panbiogeographic methodology is
from geological history. Panbiogeography offers a homology connection with
geological/geomorphic features to predict a particular geological history
associated with a particular track or standard track.
>I may have difficulties in defining "forcing", but I apply the term because
>(as has been established in earlier posts), CGH Panbiogeography accepts
>only 5 different types of trans-oceanic baselines (corresponding to the
>major ocean basins), thus forcing all possible transoceanic patterns in
>only 5 pigeonholes.
When it comes to assigning ocean baselines there are indeed only five ocean
basins. Baselines are not confined to ocean basins however.
>Sorry - when I said less detailed geological data, I meant data that did
>not contain any historical information. That seems to be undisputed.
As I understand the panbiogeographic method, the correlation is between a
spatial pattern of biological distribution, and a spatial pattern of
geology involving earth history. If one correlates a track with a fault for
example, there are historical speculations by geologists about the history
of that fault. From the baseline correlation one has a spatial connection
by which to consider the origin of the correlated track/s with the
hypothesized history of the feature concerned.
>> I get the impression that Hovenkamp views the panbiogeography
>>book as the be all and end all of post-Croizat panbiogeography.
>I had expected it to be an up-to-date review of the whole field, yes.
We certainly anticipated that the book would not meet all needs. I think
people in general will see the book as an introductory overview. It
certainly has been useful in that respect from the feedback I have received
from some students involved with biogeography courses. It would certainly
be nice to develop a more comprehensive book, but given our current
resources I don't know when or if that will happen. Its still a problem
getting journal articles past some of the biogeographic thought police let
alone getting support for doing a book. (One thing I will say is that we
were indeed fortunate with Oxford University Press in that their editorial
policy was so professional, and we had extremely good review feedback from
an anonymous reviewer who provided detailed and focused advice on what
approach to take that led to the final product).
>Croizat's writings cover several thousands of pages - it would be a
>statistical miracle if it was *all* wrong ;-)
Agreed. However, Mayr would strongly disagree with you!
>Seriously - what strikes me when reading Croizat is the stubborn refusal to
>accept current maps as relevant for the explanation of distribution
>patterns. A world of difference with the straitjacket of (current) ocean
>basins imposed on biogeographical data in CGH Panbiogeography.
Croizat used ocean basins to define global homology patterns so this does
not lie just with CGH panbiogeography.
>>No it does not. It simply means that the book was not focused on details of
>>phylogeny. It is obvious that one may draw tracks for any phylogeny. The
>>more detailed the phylogeny the more track connections between related taxa
>>one may draw. Simple as that.
>And the references?
Not forgotten. Just could not do that from home. I think anyone really
interested in biological and spatial relationships needs to become familiar
with the panbiogeographic literature in general. Since Hovenkamp finds
panbiogeography to be invalid as a methodology, any application of
biological phylogenetics will be uninformative. However, for those who do
see some validity of spatial analysis and are interested in its past or
potential applications to form systematics Craw (1988) has a general
section on panbiogeography and phylogeny and Craw's (1989) paper gives an
example of phylogenetic analysis integrated with track analysis for the
Chatham Islands. I doubt Hovenkamp will find it satisfactory, but for those
interested in panbiogeography it will provide some indication of the
Heads' (1999) paper provides some discussion of phylogeny for Abrotanella
(cited in the other earlier posting). Heads compares inferences made about
dispersal by Swenson and Bremer with spatial correlations with tectonic
features that might suggest an alternative history. Also in the recently
published Mexican book I take the phylogeny proposed by Swenson and Bremer
to show how their phylogenetic sequence provides for two nodally connected
vicariant trans-Pacific tracks within the Blennospermatinae. I also point
out how biological phylogenetic relationships proposed for Nothofagus fail
to denote which geographic sector of the earth is involved with the origin
and evolution of the genus.
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