dispersal fantasy

Robin Leech releech at TELUSPLANET.NET
Thu Jun 27 10:25:30 CDT 2002

Hi Pierre,
In 1964, I was studying the spiders of the Lake Hazen area, northern
Ellesmere Island, NWT, Canada, at about 83 degrees north - near the
northwest corner of Greenland.
The geological evidence said that during the Wisconsinan Glaciation, the
entire area had been covered by glaciers.  The biological evidence - at that
time mostly from botanical evidence, but also from my spiders - said that
there had been a refugium ON northern Ellesmere Island.
In my final year of my Master's degree, I was taking a course in Pleistocene
Geology (Surficial Geology, mudpie geology, your choice), that was a seminar
course - we, the students, had to provide the seminars.  My seminar involved
trying to solve the geological/biogeographical problem on northern
Ellesmere Island.  I came up with the idea that the the ice may not have 
covered ALL sites at one time, and as the ice advanced and retreated, 
it left, always, an area even as small as 1 square kilometre, ice free.  
Now ice does not advance and retreat at great speeds, to the fauna and 
flora of the area could advance and retreat with the ice.
I called it a "wandering refugium".  This is a term now widely used to cover
the problem of conflicting evidences from these different disciplines.
This was my way.  Perhaps we have to look at other ways to "marry"
conflicting evidences.

----- Original Message -----
From: "pierre deleporte" <pierre.deleporte at UNIV-RENNES1.FR>
Sent: Thursday, June 27, 2002 4:50 AM
Subject: Re: dispersal fantasy

> A 22:27 27/06/2002 +0200, Peter Hovenkamp wrote :
> >To me, the basic problem here seems to be how we go about confronting
> >geological theory with biogeographical evidence.
> Agreed, and hence what is considered relatively strong or doubtful
> in geology or historical biogeography. Apparent conflict of course appeals
> to improved explanation.
> >John seems to want to collect a whole lot of biogeographical evidence,
> >this evidence to derive a biogeographical statement with some degree of
> >generality, and then confront geology with that statement.
> Seems to. I still don't grasp the general rule for making a geological
> prediction from a "baseline" (series of redundant tracks), without
> implementing some "biogeographical evolutionary model". Would some model
> implemented, then panbiogeography would be comparable to other approaches
> in historical biogeography .
> >Pierre seems to accept a "piecemeal" approach, which confronts each piece
> >of biogeographical evidence with the geological theory separately, and
> >returns a "narrative" which deals with the similarities and differences.
> >Is that more or less a correct interpretation?
> I't's a possible debate, but not my own proposition. I perfectly accept
> that a general pattern emerging from largely sampled biotas (and not only
> considering separate lineages independently) can be taken into account. If
> such a pattern emerges from "noise", then some common historical fate of
> the biotas is likely. My question in is: which pattern means what, and
> Clearly, I suggest that not any arbitrary designed pattern goes.
> Thus I question biogeographers of "areas" for the meaning of there areas
> and the way they interpret the biological of geological connections
> areas, I question biogeographers of distribution limits (Peter ?!) the
> way, as so goes for proponents of tracks and baselines. What does this
> mean, and how do you draw explanations or predictions from that ?
> >I suggest that, in the long term (when we're all dead...) it will come to
> >the same thing: when a lot of conflicting evidence emerges, something
> >have to break, and alternative theories will have to be considered.
> All right for alternative theories, confrontations and new suggestions.
> mean theories, let's talk of theories.
> A classic vicariance theory is that speciation was principally allopatric,
> that areas of endemicity may be defined, and that redundant pattern of
> areas connected by the phylogenetic relatedness of the taxa they harbour
> indicative of general splitting events (barriers) having affected the
> biotas in the past, or alternatively of oriented dispersal across such
> barriers.
> A variant vicariance theory (Hovenkamp's approach, in short) considers the
> same way that allopatric speciation is the general rule, but that the
> problem at stake is the identification of barriers, and that redundant
> distribution limits between sister taxa is the right pattern to be
> for (rather that cladograms connecting pre-defined areas of endemicity),
> the way eluding the problem of very large distributions (as irrelevant)...
> All this is debatable.
> Now, panbiogeography looks after redundant tracks = baselines. But what is
> the panbiogeographic theory?
> >  That
> >may be a geological theory (new evidence for land bridges across the
> >Mozambique channel), or it may be about the biogeographical evidence
> >(someone finding chameleons can swim after all..., or revealing fatal
> >in the cladograms).
> >Ultimately, it's about strength of evidence. I would need pretty strong
> >evidence to convince me of the effectiveness of homeopathic medicine -
> >some recent transoceanic dispersal hypotheses come close to that in their
> >implausibility in the light of other evidence...
> Yes. You mean evidence. My point is that patterns of any kind are not
> relevant evidence for anything, without an interpretative theory. A purely
> "structural" biogeography disconnected from interpretative theories would
> not make more biological sense than a purely "structural" systematics.
> Pierre.

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