Centres of origin
pierre.deleporte at UNIV-RENNES1.FR
Mon Apr 22 16:26:13 CDT 2002
A 22:59 21/04/2002 -0600, Alec McClay wrote:
>A lot of the pronouncements about centres of origin that we depend on in
>biocontrol seem to be made just on the basis of intuition or expert
>authority, without any indication of how these conclusions were reached.
>For instance, Cirsium arvense occurs as apparently a native species across
>most of Europe and large parts of northern Asia. Does this whole vast range
>count as its "centre of origin" or does it make sense to look for some more
>restricted area that is the true "centre of origin"? I've read statements
>that it "probably originated in the Eastern Mediterranean area" or "in the
>Caucasus". (I'm writing from memory but I can find the references if anyone
>is interested.) These statements were completely unaccompanied by evidence.
>What I'm trying to find out if it is possible to make statements like this
>that would actually be supported or testable by biogeographic evidence (or
>any other kind of evidence for that matter). The comments by Curtis Clark
>and Bernard Baum so far suggest that it is not - the centre of origin is
>"mostly unknown", "theoretically problematic", and "hard to imagine how one
>would discover it". Is this the general consensus in the field?
At least, IMO, you put questions the right way. Which present pattern of
distribution should a "center of origin" leave on Earth after some time of
evolution of lineages, geology and distributions ? Under which model(s) of
evolution? If we cannot answer such questions, we have effectively no
logical way to infer the location of centers of origin. If we think we can,
well let's try it, and justify the model(s) of evolution implemented.
For example, John Grehan recently suggested that a panbiogeographic
"baseline" could indicate a center of origin. The question is: why ? What
is a baseline, and under which model of evolution of distribution of taxa
on Earth should such a baseline indicate a center of origin ? And what are
the conditons of validity of the model, i.e. the external theory and
evidence justifying the adoption of this specific model in the general or
specific case against other possible ones ?
It does not seem to me that this (possibly still incomplete) series of
questions is frequently asked, answered and explicitly argued by people
talking of centers of origin.
(I took this recent example of John's by pure convenience, it's not a
specific charge against panbiogeography).
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