dispersal fantasy / panbiogeography

pierre deleporte pierre.deleporte at UNIV-RENNES1.FR
Mon Jul 1 18:51:00 CDT 2002

A 10:19 01/07/2002 -0400, John Grehan wrote :
 >>Pierre Deleporte wrote:
 >>OK, I have to go and search for the answers by myself. I naively thought
 >>that if the answers existed, they would have been written in Craw et als.
 >>book, in the introductory chapter, or could be stated in a few sentences
 >>by trained practitioners of panbiogeography.
 >Some or all of the 'answers' may well exist in the Craw et al. book. I did
 >not meant to suggest otherwise.

OK, so I'll re-read the book throughout, not only the introductory chapter !
You're not so bad a propagandist, after all... Try to answer myself some of
my questions, and then ask only the possible remaining ones.

 >>An approach resting on an incomplete set of explanatory models or theory
 >>will inevitably produce varying applications. Seems perfectly natural to me.
 >It seems like what Pierre is looking for is a recipe so the cake will
 >always come out of the oven the same way. Alternatively, panbiogeography
 >may be viewed as having a wide latitude of possibilities.

I simply want to be check if the recipe is susceptible to produce cake, or
at least something approaching cake, or some fairly edible feature, before
putting anything in my oven... maybe too much gastronomically suspicious,
but I'm French, you know... :-)
Successful recipes effectively give you some guaranties that a cake will
come out, approximately the same way everytime you try it. Some recipes
have several variants, but the kind of cake you'll get is pedictable.

 >>Some people want to understand an approach before using it. I suggest they
 >>should not be shamed of that... "philosophically speaking".
 >I concur wholeheartedly, and regret any implication to the contrary.

You did not exactly tell the contrary, you simply were not enthusiastic
(and still are not) of providing direct answers to some questions
susceptible to facilitate understanding. But that's it, no offense.

 >>I appreciate the time Pierre has taken to raise the issues of concern to
 >>him. They will contribute to my understanding of how at least some
 >>systematists have difficulty with understanding panbiogeography and perhaps
 >>highlight some issues that I can address in the future.

Thanks. My concern is for understanding of all approaches in biogeography.
As far as it goes, some approahces (or parts of) implement explicit
explanatory models: their logics are thus  debatable. Others (or parts, or
variants of) do not implement explicit models, or a vague way: their logics
are thus much less, or not at all, debatable. That some people find
heuristic value in them thus requires, effectively, closer examination of
the implications of their interpretations. The possible implicit reasoning
of the practician becomes matter for methodological analysis (or

Thanks anyway for discussion, if I was of some help in this, it's OK for
me. My little experience of methodological debates tells me that, when your
colleague obstinates in not answering a given question and persistently
talks of something else, you likely made a relevant point... Destinated to
ripe with time, hopefully...

A last example: "shortest lines" between taxa localities (tracks). Why
would the shortest line as the crow flies be relevant for biogeographic
inferences? Isn't this implying some notion of uniformity of the landscape,
relatively to the spatial abilities of the taxa ? Or of lack of relevant
barriers inside this landscape ? (just to refer to the combined
dispersal-vicariance model supposed to be standing behind the
panbiogeographic method according to Craw et al.). We already discussed
this point some months ago, and your answer was that parts of tracks may
effectively happen not to be in straight line as the crow flies: one has to
decide in this matter (I took an example like that of a recent plain-living
organism standing both sides of the Himalayas: the shortest relevant
"track" could be round the mountain rather than across it...). If yes, such
a possible exception to "straight line analysis" would imply some
assumption about dispersal abilities of the taxa (like in the "plain living
organism" example above), which the panbiogeographic method is supposed not
to implement. And if distances matter (e.g. for discriminating "main
massing" from the rest of a track), isn't a model of "biogeographical
process proportional to distance" necessarily implied ? If not, absolute
distances could be "corrected" with some appreciation of organisms
performances (whatever) regarding different qualitative aspects of the
landscape (whatever).

By the way, possibly you will not tax me of narrow-minded
anti-panbiogeographic ostracism? I don't say you meant it, just wondering.
Maybe you could admit that some people are sincerely not convinced by
panbiogeography as a method, in its present state of development, despite
their efforts to grasp the meaning of it. Which is neither ostracism and
anti-propaganda, nor mere thoughtless aknowledgment of current
methodological fashion.

best, Pierre

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