Geography Reference
In-Depth Information
Figure 5.6
Resolutions of a taxon with a missing area. (a) Taxon with a missing
area; (b-f) five possible solutions placing it in all possible positions in the cladogram.
AF, Africa; AUS, Australia; NA, North America; SA, South America.
• Resolved area cladograms from the different taxa analyzed should be
obtained under the same assumption because the common pattern for
all taxa would have to be explained by the same process.
• The sets of resolved area cladograms obtained under the three as-
sumptions should be successively inclusive, namely, those obtained
under assumption 0 would be included within those obtained under
assumption 1, and the latter would have to be found within those ob-
tained under assumption 2. The reason is that the processes are ad-
ditive (each assumption incorporates or includes those of the preced-
ing assumption).
The first requirement is not valid because different taxa can be affected
by different processes, although they may show a common pattern. In re-
lation to the second requirement, Ebach and Humphries (2002) suggested
that it is violated by the use of assumption 0 when introducing artificial in-
ternal nodes for widespread taxa.
On the basis of the information from the different resolved area cladograms,
a general area cladogram is derived. It represents a hypothesis on the
biogeographic history of the taxa analyzed and the areas where they are
distributed.
The general area cladogram that results from the analysis may be fals-
ified with a geological area cladogram or geogram (Swenson et al. 2001).
This is an area cladogram based on geological or tectonic data (Morrone
and Carpenter 1994; Rosen 1985; Seberg 1991). Cladistic biogeographic
analyses that include this step are scarce (Seberg 1991; Swenson et al.
2001; van Welzen et al. 2001). Another way to evaluate general area clado-
grams is through the calculation of items of error (Morrone and Carpenter
1994; Nelson and Platnick 1981). The procedure consists of determining the
terminal number of nodes and areas that are necessary to add to the tax-
on-area cladogram so that it agrees with the general area cladogram, that
is, to map one cladogram onto the other to determine their congruence. The
smaller the number of nodes and terminal areas that must be added, the
