Biogeographic units and classification

Don McAllister mcall at SUPERAJE.COM
Mon Apr 26 12:28:01 CDT 1999

John Grehan wrote:

> Don McAllister wrote
> 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.

Equal-area grid analysis has utility beyond distribution densities.  It can, for
example be used ot quantify what level of endemism is being considered - so many
grid cells, equivalent to so many hundred square km.

But its chief advantage is that you can identify areas that are not constrained by
large aribitrary units like continents.  Where are taxa and clades located, rather
than just present or absent in a continental area. To what degree do clades or
species overlap?  To what extent do endemic species occur in areas glaciated during
the Wisconsins?  How much endemism is there in the Pacific Plate?

How much are patterns explained by vicariant events and how much by climate?  This
helps take biogeographic questions out of endless argument and expose hypotheses to
quantitative testing.

> don

Don McAllister


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