Vascular Plant and Vertebrate Inventory of Saguaro ... - USGS

leaf-nosed bat (Macrotus californicus), western
mastiff bat (Eumops perotis), little brown bat
(Myotis lucifugus), and western yellow bat
(Lasiurus xanthinus).
Discussion
Biogeography
As noted in the other chapters, the biology of
the district reflects a fascinating geography. The
district is located within two major watersheds,
the Santa Cruz River on the west side of the
Rincons and the San Pedro River on the east
side. More importantly, the Rincon Mountains
contain elements of several major biogeographic
provinces, including the Sonoran Desert to the
south and west, the Rocky Mountain region to
the north and east, the Chihuahuan Desert to
the east, and the Madrean region to the south.
The Rincon Mountain District also hosts a
significant elevational range, from 814 m (2,670
ft) to 2,641 (8,665 ft), and a number of different
plant communities. As a result, the district
contains mammals that represent several different
biogeographic origins, including a large number
of species not present in the Tucson Mountain
District. Thus, the Rincon Mountain District’s
mammals include classic Sonoran Desert species
(e.g., the round-tailed ground squirrel); species
strongly associated with the Madrean region
and central America (e.g., the white-nosed coati,
collared peccary, and southern long-nosed bat);
“northern” species (e.g., the American black bear
and northern raccoon); and typically western
species (e.g., the Botta’s pocket gopher and
American badger).
A number of species, particularly bats
and rodents, are on the edge of their range in
the district. Our documentation of the fulvous
harvest mouse is the furthest northwest location
ever recorded for this species (Hoffmeister
1986). Similarly, the Rincon-Catalina complex
represents the northwestern-most site for the
yellow-nosed cotton rat and the northeastern-
most site for the Arizona pocket mouse. In
contrast, several species we did not capture
are found just southeast of the district in the
Santa Rita Mountains and nearby sky island
84
mountain ranges including the pygmy mouse
(Baiomys taylori), fulvous cotton rat (Sigmodon
fulviventor), hispid pocket mouse (Chaetodipus
hispidus), and others (Hoffmeister 1986). It is
possible that with more intensive effort these
species might be found in the district. Indeed,
Davis and Dunford (1987) suggest that the
yellow-nosed cotton rat has only recently
migrated into the Rincon Mountains. Lowe
(1992) and Swann et al. (2005) have discussed
the biogeography of reptiles and amphibians in
the Rincon Mountains and factors that possibly
influence distribution; it seems possible that these
same patterns occur for smaller mammals as well.
Habitat Associations
Despite its close proximity to Tucson, the district
has had only a few mammal studies. Our study
represents the first comprehensive inventory of
the district below the high country (which was
studied by Davis and Sidner 1992), and the first
to quantify relative abundance and distribution
of species. We trust that it will provide a good
baseline for evaluating future changes in the
mammal community at the district.
Our study indicates that the Rincon
Mountains have a typical assemblage of other
sky island mountain ranges, with the exception
of some semi-desert grassland species and
the addition of a strong desert component. It
is noteworthy that species richness for small
mammals was similar between middle and high
elevations. Overall, species richness was highest
at the lowest elevations and decreased at higher
elevations. There is a strong desert component
in the mammalian community of the district,
with a large number of species, ranging from
the Sonoran Desert pocket mouse to mule deer,
found only at lower elevations. However, a few
species such as the Abert’s squirrel and Mexican
woodrat were found only at high elevations. The
middle elevations are richest overall, containing
components of both deserts and forests.
We did not attempt to separate riparian
from upland species richness in this study.
However, as would be expected, wet riparian
areas at all elevations stand out as hotspots of
mammal diversity. Davis and Sidner (1992)