Centres of Endemic?

[Fred Rickson]

A number of times, John has eluded to a "panbiogeographic book."  I expect
he is too modest to list it, but I have just finished reading it and give
you "Panbiogeography: Tracking the History of Life" R.C. Craw, J.R. Grehan
and M.J. Heads, Oxford Biogeography Series #11, Oxford University Press,
NY. ISBN 0-19-507441-6.  It might not change minds on the basic value of
the methods involved, or of the possibility of empirical studies in the
field, but it does present a very well written analysis of the field.  And,
it sure beats reading and trying to understand Croizat.  I enjoyed the read
and found myself asking questions as to whether or not I could use the
insight in some of my plant distributional-historical problems.  We all
come to know the geographical distributions of our favorite
organisms.....maybe we can make a little more out of it than just drawing
lines around all of the dots.

Best,

Fred R. Rickson
Professor of Botany
Department of Botany
Oregon State University
Corvallis, Oregon
USA  97331

Tel: (541) 737-5272
Fax: (541) 737-3573
email: ricksonf at bcc.orst.edu

----------
> From: John Grehan <jrg13 at PSU.EDU>
> To: TAXACOM at USOBI.ORG
> Subject: Re: Centres of Endemic?
> Date: Friday, November 19, 1999 5:26 AM
>
> >From at least one perspective (mine!), centers of endemism are relative.
The
> method outlined by McAllister may correspond to centers of main massing
in
> panbiogeography. It is possible to recognize gradients of taxonomic
density
> with
> respect to given geographic boundaries, and the use of a grid provides a
> consistent
> measure of relationship to area.
>
> The other concept that has been applied to endemism is the "area of
> endemism". This concept represents the view that there are "natural"
> geographic boundaries that define the endemism. A simple way of
describing
> such areas is to say that any defined area that contains an edemic taxon
is
> an area of endemism. In this context the area is an arbitrary designation
> since there is no necessary homology between the origin of the taxon's
> distribution and the geographic limits of the area. Thus a taxon endemic
to
> Tasmania might also be said to be endemic to Australia, or Australasia,
or
> the SW Pacific, the Old World, the entire world. There is no natural
limit
> to the unit area to which a taxon might be endemic. Further,
biogeographic
> analysis of so-called areas of endemism (ranging from local ecological
> areas, biomes, provinces, regions etc.) are biogeographic composites
since
> they involve taxa with spatially different tracks. This is the
fundamental
> problem of attempts to construct "natural" biogeographic classifications
of
> areas of endemism.
>
> One may, for descriptive purposes draw geographic outlines to enclose
areas
> that one might characterise in a particular way, but I would argue that
> these areas are descriptive only, and when it comes to the analysis of
> their biota, it is necessary to examine distributional significance in
> terms of different criteria (such as the spatial geometry of the
> distributions themselves).
>
> In reference to Africa one could examine and compare the traditional area
> of endemism approaches to that of panbiogeography in a chapter on the
> biogeography of Africa (which examines the question at continental as
well
> as local ecological scales) in the 1999 panbiogeography book
>
> John Grehan