Biogeographic units and classification

[John Grehan]

Don McAllister wrote

>One question that has not been properly addressed by the luminaries cited, is
>how are the <geographic> units used, determined.  Most have arbitrarily used
>continents or parts of them, islands, lakes, etc.  Very few people have used
>equal-area grids, untied to prior geographic concepts, to identify hotspots
>of species, endemic species, or higher taxa.

There is a section of the panbiogeography book that acknowledges the utility of
equal area grid analysis, particularly for mapping distribution densities. Even
though these grids are of equal size, they are still arbitrary units, so they
do not, in my mind, provide biogeographic homologies. However, I see
potential for an interrelationship between track/node analysis and grid
analysis.
The latter, in particular, may be the best way to assign centers of main
massing, since main massings (centers of diversity) can influence the
orientation
of a track.


>The other problem biogeography has often ignored, is what higher taxa or if
>you wish clades, have to contribute to understanding biogeographic patterns.
>The majority of studies emphasize species-level taxa.  But consider that the
>bumblebees are most speciose in the Andes whilst the higher clades are in the
>Himilayas.  Those facts deserve consideration in biogeographic analyses.

I agree that this is an important consideration. I understand that efforts to
develop a weighting system by some cladists are directed to this problem.

The general question of diversity and rank is also discussed briefly in a
section on African biodiversity in the panbiogeography book (I don't want
to seem as if I am claiming we covered every biogeographic subject under
the sun, but there were a wide range of issues considered). The same point
is made about species-centric approaches distorting global biodiversity.

John Grehan