Geography Reference
In-Depth Information
during Pleistocene pluvial intervals. Full regional deserts formed during intergla-
cials and reached their maximum extent after the Wisconsinan glacial. As a con-
sequence, sister taxa in alternate desert areas might share common ancestry at
one of at least two broad ages: the Late Miocene to Pliocene, along with tectonic
events that underlay the early development of regional deserts, or the Pleistocene
in association with climatic oscillations. Several authors have postulated models
to account for the biotic evolution of these deserts (Grismer 1994; Hubbard 1973;
Morafka 1977; Morafka et al. 1992; Murphy and Aguirre-León 2002), discussing
specific vicariance events. Riddle and Hafner (2006) developed a five-step ap-
proach to analyze the relationships between North American desert areas, com-
bining phylogeographic hypotheses, PAE, and primary and secondary BPA.
Riddle and Hafner (2006) analyzed twenty-two taxon cladograms from mam-
mal, bird, reptile, amphibian, and cactus phylogroups, with species distributed in
a subset of the North American warm desert biota that they considered adequate
for their study. To identify the areas of endemism, they applied PAE to eleven core
warm desert distributional areas. They used primary and secondary BPA to exam-
ine biogeographic structure across the areas found with PAE. PAUP version 4.0
(Swofford 1999) was used for both PAE and BPA.
The PAE of the eleven areas of distribution, which was run removing sequen-
tially areas lacking many endemic species, led to the identification of four areas of
endemism (
fig. 5.12a
)
: Continental East (Trans-Pecos, Coahuilan, and Zacatecan
areas), Continental West (Sonoran and Coloradan areas), Peninsular South (Mag-
dalenan and San Lucan areas), and Peninsular North (Cirios area). A single most
parsimonious primary BPA cladogram (
fig. 5.12b
)
was produced, with 120 steps,
a consistency index of 0.70, and a retention index of 0.58. In the cladogram,
Continental West and Continental East are sister areas, and Peninsular North and
Peninsular South are sister areas. The high number of synapomorphies suggests
common vicariance patterns, although there are several homoplasies, especially
between Continental West and Peninsular North, and Continental West and Pen-
insular North and Peninsular South. Secondary BPA resulted in a cladogram (
fig.
5.12c
) with duplications involving all areas except Peninsular South.
