Centres of Endemic?

[John Grehan]

>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