The distributions of animals are influenced by geographic, vegetational, and altitudinal factors. The Mesa Verde is intermediate in geographic position and altitude between the high Southern Rocky Mountains and the low southwestern desert. For this reason, we find on the Mesa Verde (1) a preponderance of species having wide distributions in this part of the country, and having relatively wide ranges of tolerance for different habitats, (2) a lesser number of exclusively montane or boreal species than occur in the higher mountains to the northeast of the Mesa and that may reach the limits of their ranges here, and (3) a small number of species of southern or Sonoran affinities. Fifty-four species are recorded above.
Forty-one of these species are represented by specimens from the Park. Thirteen additional species in the list have been seen in the Park.
On the Grand Mesa, which is more elevated than, and some 110 miles north of, the Mesa Verde ([see Figure 1]), 55 per cent of the species of mammals have boreal affinities and the other 45 per cent are wide-spread species (Anderson, 1959:414). Boreal species from the Mesa Verde are Sorex vagrans, Sylvilagus nuttallii, Spermophilus lateralis, Marmota flaviventris, Tamiasciurus hudsonicus, Microtus montanus, and Microtus longicaudus. These seven species comprise only thirteen per cent of the mammalian fauna of the Mesa Verde. Other boreal species that occur in the mountains of Colorado on the Grand Mesa or elsewhere (Findley and Anderson, 1956:80) and that do not occur on the Mesa Verde are Sorex cinereus, Sorex palustris, Ochotona princeps, Lepus americana, Clethrionomys gapperi, Phenacomys intermedius, Zapus princeps, Martes americana, Mustela erminea, and Lynx canadensis. The 47 species from the Mesa Verde that are not exclusively boreal make up 87 per cent of the mammalian fauna. Most of these are wide-spread species and are more abundant in the deserts or other lowlands than in the coniferous forests of the highlands, for example the eight species of bats, and Sylvilagus audubonii, Thomomys bottae, Taxidea taxus, Bassariscus astutus, Canis latrans, Cynomys gunnisoni, Reithrodontomys megalotis, and Lepus californicus. A few of the wide-spread species are more common in the highlands than in the lowlands, for example Ursus americanus, Felis concolor, Castor canadensis, Erethizon dorsatum, and Cervus canadensis, and the ranges of three of these, the bear, mountain lion and wapiti, are more restricted today than formerly. A few species find their favorite habitat and reach their greatest abundance in altitudinally and vegetationally intermediate areas such as upon the Mesa Verde, or in special habitats, such as the rock ledges, and crevices that are so abundant on the Mesa. Examples of this group of species are Spermophilus variegatus, Peromyscus crinitus, Peromyscus truei, Neotoma cinerea, and Neotoma mexicana. One species, Dipodomys ordii, is restricted to the desert. Species that are restricted to the desert and that occur in Montezuma County, Colorado, but that are not known from the Mesa Verde are Ammospermophilus leucurus, Perognathus flavus, and Onychomys leucogaster.
Species known to have changed in numbers in the past 50 years are the mule deer that has increased, and the prairie dog that has decreased. Possibly beaver have increased along the Mancos River. The muskrat, mink, beaver, and raccoon usually occur only along the Mancos River, as there is no other permanent surface water in the Park.
Species such as the bighorn and the marmot that are rare within the Park, or those such as the chickaree, the prairie dog, the wandering shrew, the montane vole, and the long-tailed vole that occupy only small areas of suitable habitat within the Park are the species most likely to be eliminated by natural changes, or through the activities of man. For example parasites introduced through domestic sheep that wander into the range of bighorns within the Park might endanger the bighorn population. An increase in grazing activity, road building, and camping in Prater and Morfield canyons might eliminate the small areas of habitat occupied by the montane vole and the wandering shrew. Fire in Chickaree Draw could destroy all the Douglas fir there, and consequently much of the habitat occupied by the chickaree.
Probably some species inhabit the Mesa that have not yet been found, but they are probably few, and their discovery will not alter the faunal pattern in which the few boreal species occupy restricted habitats in the higher parts of the Mesa, and a preponderance of geographically wide-spread species occupy all or most of the Mesa, and surrounding areas. Additional bats are the species most likely to be added to the list.
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LITERATURE CITED