Geography Reference
In-Depth Information
Figure 1.1
Flowchartwiththefivestepsofanevolutionarybiogeographicanalysis.
Biotic components are sets of spatiotemporally integrated taxa that coexist
in given areas. Their identification is the first stage of an evolutionary
biogeographic analysis. There are two basic ways to represent biotic com-
ponents: generalized tracks and areas of endemism. The former are studied
by panbiogeography, whereas the latter are the units of cladistic biogeo-
graphy.
Panbiogeography emphasizes the spatial or geographic dimension of
biodiversity to allow a better understanding of evolutionary patterns and pro-
cesses (Craw et al. 1999). A panbiogeographic analysis comprises three
basic steps: (1) constructing individual tracks for two or more different taxa,
(2) obtaining generalized tracks based on the comparison of the individu-
al tracks, and (3) identifying nodes in the areas where two or more gener-
alized tracks intersect. Individual tracks are the basic units of panbiogeo-
graphy, representing the primary spatial coordinates of species or supra-
specific taxa, which operationally correspond to line graphs connecting the
different localities or distributional areas of a taxon according to their geo-
graphic proximity. Generalized tracks result from the significant superposi-
tion of different individual tracks and indicate the preexistence of ancestral
biotic components that became fragmented by geologic or tectonic events.
Nodes are complex areas where two or more generalized tracks superim-
pose and are usually interpreted as tectonic and biotic convergence zones.
Areas of endemism are areas of nonrandom distributional congruence
between different taxa (Morrone 1994b). Müller (1973) suggested a protocol
that has been applied to identify areas of endemism and that consists of
plotting the ranges of species on a map and finding the areas of congruence
between several species. This approach assumes that the species' ranges
are small compared with the region itself, that the limits of the ranges are
known with certainty, and that the validity of the species is not in dispute.
Cladistic biogeography assumes a correspondence between the phylogen-
etic relationships of the taxa and the relationships between the areas they
inhabit (Platnick and Nelson 1978). Cladistic biogeography uses information
