Date of Award:
Doctor of Philosophy (PhD)
J. Juan Spillett
Objectives of this study were: (1) to determine the status of the utah prairie dog (Cynomys parvidens, Allen), a rare mammal endemic to southcentral Utah, and (2) to identify habitat factors which limit densities of this species. Seven components of the habitat were studied: barriers, other animals, soil, temperature and precipitation, topography, vegetation, and water. Prior to collection of habitat data, virtually all populations of the species were found by extensive searching and interviewing; the number of animals and the area occupied were determined for each population.
Results justified the endangered status of the Utah prairie dog. Area occupied by this prairie dog was reduced by an estimated 87 percent during the past 50 years. During this time, the animals disappeared from 34 localities. Recently, total numbers also were reduced: between 1970 and 1971, the total population dropped from an estimated 8, 600 animals to 5, 700. Only 48 substantial populations existed in 1971. Six other populations were exterminated the preceding year by rodent control.
Although the loss of prairie dogs between 1970 and 1871 resulted from rodent control, another loss between 1971 and 1972 resulted from drought. A drought decimated all populations in regions without water. Topographic region, which reflected water available to plants, was more strongly correlated to density of this prairie dog than any other parameter (r20' • 67).
The crucial role of water was confirmed by analysis of vegetative parameters. Since grasses, forbs, and shrubs have distinctive water contents, they indicated prairie dog response to plant water. Forb cover, which contains the highest relative water content, was the only type of cover that was positively correlated to the density of these animals. Shrubs, with the lowest water content, were negatively correlated; and grasses, with an intermediate water content, were neutral relative to density.
Two other parameters also demonstrated the critical nature of water: the mean number of grasses, forbs, and shrubs, and heterogeneity among plant communities. No other parameters were significant (p :::_. 05) in multiple regression. Together, these explained 75 percent of the variability in abundance of the Utah prairie dog. The mean number of grasses, forbs, and shrubs was negatively correlated with density; coefficients of this parameter probably reflected the time required for prairie dogs to select plant parts with adequate water. On the other hand, heterogeneity among plant communities was positively correlated to density, and indicated emergency sources of plant water. Such water probably allowed prairie dogs to avoid population reductions otherwise associated with drought.
The critical nature of plant water is especially meaningful in light of long-range drying trends. The Utah prairie dog's habitat has become progressively drier during the past several thousand years. If these trends continue, the animal may become extinct. However, their possible extinction can be delayed by transplanting animals to sites adjacent to streams or irri[;ated fields. Transplanting also can help solve the secondary problem of rodent control: since prairie clogs are often eradicated on private lands, transplant sites should be controlled by the public. Public lands in southern Utah usually contain little water; therefore, purchase of certain private lands with adequate water for the animals is a key to managing this unique prairie dog.
Collier, G. Donald, "The Utah Prairie Dog: Abundance, Distribution, and Habitat Requirements" (1975). All Graduate Theses and Dissertations. 2760.
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