Biogeographic memory

[P.Hovenkamp]

At 12:44 PM 9/4/01 -0400, you wrote:

>>One of the reasons why I find Panbiogeography difficult to understand may
>>be that it uses a lot of terms in a sense that is distinctly different
>>from common usage. Thus,  Panbiogeography builds a "parallel universe'  of
>>terms, which is hardly accessible from this one.
>
>I agree. The new research program has necessitated both new terms and new
>definitions for old terms. This appears to represent a normal function in
>science where new research programs are instituted  - as acknowledged by
>Hovenkamp. There was the same kind of hurdle with the introduction of
>cladistics, and more recently molecular systematics.

As far as I remember, with the introduction of cladistics only the term
"monophyly" changed  meaning (was clarified, as many would say). Most other
terms were new introductions.

>>Thus, "dispersal" does not mean dispersal, and "tracks" are not tracks,
>>"homology" is not homology (not quite, at least), "center of origin" is
>>not center of origin (or is it?), "main massing" need not be main nor
>>massing (see p. 79, where a single occurrence in the Comoros is treated as
>>a "main massing"),  and now "phylogeny" turns out to be not phylogeny (but
>>note how in the examples of Ch. 4 the term phylogeny seems to be used in
>>its conventional meaning).
>
>These terms are simply not what they might be assumed to be in traditional
>Darwinian biogeography.
>
>>I realize that such terminological confusion is inherent in the
>>establishment of any new research program, but I would have expected a
>>more coherent account of these terms in a book of this kind, summarizing
>>40 years of research after the first establishment of its research program.
>
>I guess 'coherence' is a judgement that the individual must make. Some
>people think we did quite well, others not.

Sorry - I intended the emphasis to be on account - not on coherent. The
terms "dispersal", "homology", "phylogeny" and "center of origin",  for
instance, are not explained in the Glossary of technical terms.  Although I
have also some problems with what I see as a lack of coherence: I already
indicated the dual usage of "phylogeny" in Ch. 4; also the notion that a
"track" can be orientated by way of a baseline suggests a leftover from the
meaning of track as dispersal route.

(...)
>>>>Would not that be enough to dismiss the claim that "their distiributions
>>>>are not distinguishable according to their different means of dispersal"?
>>>
>>>Not in my view.
>>
>>Again - how different must two patterns be to be distinguishable? My
>>earlier question about this was ignored by John Grehan.
>
>Sorry, not deliberately.My view is that any two patterns 'must' be
>distinguishable (potentially) according to a lack of biogeographic
>homology. In panbiogeography this homology criterion is not geographic
>overlap of distribution range, but corresponding or nested overlap of track

As that is almost certainly not the way Mayr used the word "different", it
would seem that the entire discussion is based on semantical differences...

(...)
>>>Since similarity of distribution range is not part of panbiogeographic
>>>method
>>
>>But similarity in baselines is. How is it possible to assign "the same"
>>baseline to different tracks if there is no notion of similarity? And that
>>similarity is decidedly arbitrary.
>
>As quoted above, I was excluding similarity of distribution RANGE. The
>similarity for shared baseline is for the tracks to cross the same
>geographic  feature. Since the track is drawn according to the minimal
>distance criterion, the selection of a baseline is not arbitrary in the
>sense, for example, that a distribution either side of the Atlantic cannot
>be given a Pacific baseline.

No? But compare fig. 3.11 b with fig. 1-10 b and c to see how a
distribution on both sides of the Pacific can be given a Pacific as well as
an Indian ocean baseline...
And to assign the same (Indian ocean) baseline to the tracks displayed in
fig. 3.3 b and 3.4 seems to me more than a little arbitrary.

(...)
>>But I asked for a summary of Croizat (1968), optionally incorporating the
>>data that have become available since.
>
>It appears that kind of treatment is yet to come.

Looking forward towards it.



P. Hovenkamp
Nationaal Herbarium Nederland - Leiden
PO Box 9514
2300 RA  Leiden
The Netherlands
hovenkamp at nhn.leidenuniv.nl
http://nhncml.leidenuniv.nl/rhb