Of the 53 mammals listed in the foregoing accounts, all but one (_Mus
musculus_) are native North American species. These fall into five
rather well-defined faunal groupings as outlined by Hoffmann and Jones
(1970:364-365). A majority (27) can be characterized as "widespread
species." Most of these have broad distributions over much of North
America; a few do not, but are widely enough distributed that it is
impossible to assign them with certainty to a more circumscribed
assemblage. Mammals from northwestern South Dakota that can be
characterized as widespread are: _Myotis leibii_, _Myotis lucifugus_,
_Eptesicus fuscus_, _Lasionycteris noctivagans_, _Lasiurus cinereus_,
_Castor canadensis_, _Peromyscus maniculatus_, _Ondatra zibethicus_,
_Erethizon dorsatum_, _Canis latrans_, _Canis lupus_, _Vulpes vulpes_,
_Ursus americanus_, _Ursus arctos_, _Procyon lotor_, _Mustela frenata_,
_Mustela vison_, _Taxidea taxus_, _Mephitis mephitis_, _Lutra
canadensis_, _Felis concolor_, _Lynx rufus_, _Cervus elaphus_,
_Odocoileus hemionus_, _Odocoileus virginianus_, _Antilocapra
americana_, and _Bison bison_. The above list is composed mainly of
volant or relatively large and mobile mammals, several of which occur
also in Eurasia or range well into the Neotropics.
A few widespread species deserve special comment. Two, the pronghorn and
bison, are typical inhabitants of the interior grasslands of North
America and might be considered steppe species save for the fact that
each has an extensive distribution beyond that region. Four other
species, _Erethizon dorsatum_, thought of primarily as a mammal of
coniferous forests, and _Ursus arctos_, _Taxidea taxus_, and
_Odocoileus hemionus_, all more or less western taxa, are not so broadly
distributed as are other members of this grouping. Of the five bats,
three are year-round residents, but _Lasiurus cinereus_ and evidently
_Lasionycteris noctivagans_ are migrants.
The remaining 25 kinds of mammals are representative of four regional
faunal groupings as follows: boreomontane species (10), steppe species
(nine), species with Sonoran affinities (four), and species of the
eastern deciduous forest (two).
_Boreomontane species._--Of the 10 mammals in this faunal group, three
(_Eutamias minimus_, _Tamiasciurus hudsonicus_, and _Microtus
pennsylvanicus_) are distributed both in the boreal forests to the north
of the plains and in montane areas to the west. Six species (_Myotis
evotis_, _Myotis volans_, _Plecotus townsendii_, _Thomomys talpoides_,
_Neotoma cinerea_, and _Ovis canadensis_) are primarily montane in
distribution and evidently reached northwestern South Dakota from the
west in late Wisconsin or post-glacial times; all but the pocket gopher
occur there now only in the vicinity of coniferous timber or rocky
buttes. The remaining species, _Zapus hudsonius_, is a glacial "relic."
The nearest populations now are far to the north, and this jumping mouse
occupies only restricted habitats in northwestern South Dakota and
adjacent regions. In Harding County, _Z. hudsonius_ presently is known
only from Deer Draw in the Slim Buttes.
_Steppe species._--Taxa intimately associated with the Great Plains are:
_Lepus townsendii_, _Cynomys ludovicianus_, _Spermophilus
tridecemlineatus_, _Perognathus fasciatus_, _Perognathus hispidus_,
_Reithrodontomys montanus_, _Microtus ochrogaster_, _Mustela nigripes_,
and _Spilogale putorius_ (subspecies _interrupta_). A few of these are
endemic to the plains, but most occur in grassland habitats beyond the
borders of the region. All clearly are well adapted to, and therefore
presumably evolved in response to, the environment of the interior
grasslands; this zoogeographic unit, then, is characterized by truly
steppe species that have relatively narrow habitat requirements and
largely concordant patterns of distribution.
The case of the spotted skunk deserves brief commentary. This species
was not taken or observed by members of our field parties and local
residents made no claim to its presence except for a few vague
recollections of spotted skunks having been seen "years ago." Visher
(1914:91), however, reported that _Spilogale_ was much commoner than
_Mephitis_ in the early part of the century. However that may have been,
_Spilogale putorius_, as currently understood, would be judged to be a
widespread species except that recent evidence strongly suggests that
the plains race (_interrupta_) is not of the same species as spotted
skunks to the west (subspecies _gracilis_). Furthermore, the ranges of
the two are not in contact. Whatever its ultimate specific affinities
may be, _S. p. interrupta_ clearly is a plains mammal, and thus is here
considered in that zoogeographic unit.
_Sonoran species._--_Sylvilagus audubonii_, _Dipodomys ordii_,
_Reithrodontomys megalotis_, and _Onychomys leucogaster_ are invaders to
the Northern Great Plains from the Sonoran region to the southwest. The
latter two, however, are rather broadly distributed on the Great Plains
and their assignment as Sonoran species is somewhat arbitrary. It is of
interest that as many as nine mammals with southwestern affinities occur
as far north as southwestern South Dakota and adjacent Wyoming.
_Eastern species._--Only _Sylvilagus floridanus_ and _Peromyscus
leucopus_ can be identified as species primarily associated with the
eastern deciduous forest. The former is limited in northwestern South
Dakota to brushy habitats in riparian communities, whereas _P. leucopus_
is restricted to relatively good stands of deciduous timber and
presently is known to occur only in Deer Draw of the Slim Buttes.
Throughout its known range in the western part of the Northern Great
Plains, _P. leucopus_ is represented by small and disjunct populations
associated with riparian deciduous timber. The known population nearest
to Harding County is on the Black Hills to the south; next nearest are
several isolated or semi-isolated populations along the Yellowstone
River in eastern Montana. Presumably, this white-footed mouse spread
northwestward into the western part of the plains region along river
systems, in company with deciduous trees, in some post-glacial period
when the climate was warmer and wetter than now. Subsequent drying
altered substantially the distribution and perhaps composition of
riparian forests, and isolated populations of _P. leucopus_ evidently
survived only in restricted areas, such as Deer Draw, many of them
probably marginal habitat for the species.
_Unverified species._--If the 10 species listed as of "unverified
occurrence," it seems highly likely that as many as eight will be found
to occur, or occurred within historic time, in Harding County. Among
these eight are one steppe species (_Vulpes velox_), three with
boreomontane affinities (_Sorex cinereus_, _Gulo gulo_, and _Lynx
canadensis_), two (_Sciurus niger_ and _Urocyon cinereoargenteus_) that
are associated with the eastern deciduous forests, and two (_Sorex
merriami_ and _Lagurus curtatus_) that are Great Basin elements.
It is noteworthy that the last-mentioned faunal unit is not known to be
represented in northwestern South Dakota.