Centres of origin

Alec McClay alec at ARC.AB.CA
Sun Apr 21 22:59:00 CDT 2002


>Date:    Thu, 18 Apr 2002 19:42:23 -0700
>From:    Curtis Clark <jcclark at CSUPOMONA.EDU>
>Subject: Re: Centres of origin
>
>At 11:50 2002-04-18, Bernard Baum wrote:
> >You need to distingusih between centre of origin and centre of diversity.
> >The two are not the same. Centre of origin is mostly unknown, and is often
> >not the current centre of diversity.
>
>And to add to this, the methodology for discovering the center of diversity
>is straightforward (define the "diversity" that interests you, measure it,
>and look for spatial modes), whereas center of origin is so theoretically
>problematic (even for a "Darwinian" biogeographer, what if that land mass
>no longer exists) that it's hard to imagine how one would discover it.

In the biological control literature there are many recommendations on
where to search for natural enemies for use in classical biological control
of an invasive exotic species. These include "the native range", "native
home", "centre of origin", "centre of diversification", etc. It's not
always clear how precisely or interchangeably these terms are being used.
It often seems to be assumed (again I'm talking here about the biocontrol
literature) that the centre of origin of a species is likely to be in the
centre of diversity of closely related species, but obviously this is not
necessarily the case. It's easy to visualize that our species of interest
might have originated in area A where it remains the sole representative of
its group, while its sister species might have given rise to a cluster of
related species in a separate area B.

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?

Alec McClay
Research Scientist, Biological Control of Weeds

Alberta Research Council
PO Bag 4000, Vegreville, Alberta, CANADA T9C 1T4

Tel:    (780) 632-8207
Fax:    (780) 632-8612
Email:  alec at arc.ab.ca




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