Geography Reference
In-Depth Information
hypothesis of primary biogeographic homology; (d) the general area cladogram fals-
ifies the hypothesis of primary biogeographic homology.
A biogeographic analysis by Donoghue et al. (2001) followed this ap-
proach when analyzing disjunctions of several taxa in the Northern Hemi-
sphere. These authors initially assigned the taxa analyzed to two general-
ized tracks (Atlantic and Pacific) and then undertook the cladistic biogeo-
graphic analysis of the taxa belonging to each of the tracks separately.
Riddle and Hafner (2006) presented similar arguments to develop an ap-
proach for the analysis of historical relationships that combines parsimony
analysis of endemicity, phylogeography, and cladistic biogeography.
Biogeographicprocessesarethosethatshapethegeographicdistributionof
taxa. There are three basic biogeographic processes: dispersal, vicariance,
and extinction (
fig. 2.5
). Once patterns have been discovered, explanations
on the processes that have shaped them are sought, and the hypotheses
can be tested until robust theories become accepted (Brown and Lomolino
1998).
Dispersal is the expansion of the distributional area of a taxon, covering
all types of geographic translocation (Myers and Giller 1988b). For classic
dispersalists (e.g., Darwin 1859; Matthew 1915; Wallace 1876), it meant the
movement by active migration or passive transfer of a species from its cen-
ter of origin, usually crossing a preexisting barrier, allowing it to colonize a
new area and, eventually, differentiate into new taxa. More recent authors
usually imply not a precise center of origin but the ancestral area where the
taxon evolved (Bremer 1992, 1995). The term
dispersal
has been used with
different and ambiguous meanings because it appears to be an explanation
of a pattern in terms of ideas about a process (Eldredge 1981).
Dispersal
hasbeencommonlyusedtodescribeprocessesactingondifferenttemporal
scales, such as the routine transport of propagules (short-term or biological
timescale), the chance crossing of barriers (short- to long-term scale), and
the change of the distributional area of a taxon (short- to long-term or evolu-
tionary timescale). It is useful to distinguish between the movement of an or-
ganism within its area of distribution, named dispersion (Platnick 1976), or-
ganismic dispersal (Wiley 1981), or intrarange dispersal (MacDonald 2003),
and extrarange or biogeographic dispersal (MacDonald 2003).
