The Influence of Topography and Vegetation on the Distribution of Small Mammals in Southwestern Utah

-The distribution of 15 species of small mammals was studied along a 160 km transect in southwestern Utah. The transect followed an elevational gradient and incorporated five community types. Ordination analysis revealed that abundance and distribution of certain small mammal species were influenced by topographic features (Hurricane Cliffs) and vegetational characteristics. The influence of physical and environmental factors on the distribution and abundance of small mammals in the southwestern United States has been well documented by numerous investigators (Hardy, 1945; Durrant, 1952; Allred and Beck, 1963; Armstrong et al., 1973; Beatley, 1976; Armstrong, 1977a). The purpose of this paper is to examine the distribution of small mammals as it relates to elevation and vegetation. We have chosen southwestern Utah for the following reasons: 1) Durrant (1952) and later Armstrong (1977a) subdivided this region into two major faunal areas as a result of mammal distribution and changes in physiography; 2) elevation varies from approximately 1950 m to 700 m over a distance of 160 km; 3) vegetational changes accompany elevational changes in this region; 4) presently, this region is being scrutinized for possible industrial development. STUDY AREA.-Eleven sampling stations for vegetation and small mammals were established in representative habitats along a 160 km transect in southwestern Utah (Fig. 1). The stations follow an elevational gradient from north of Kanab to the St. George Basin to the Nevada border. This region is located in a transition area of the Great Basin and Mojave deserts, in the Virgin River Valley Province as recognized by Durrant (1952) and Armstrong (1977a). The area is characterized by a rugged landscape with two major topographic features, the Hurricane Cliffs and the Beaverdam Mountains. The Hurricane Cliffs were formed by a major fault and rise approximately 400 m above the adjacent western areas of the St. George Basin. The Beaverdam Mountains rise approximately 2000 m and form a north-south barrier along the western edge of Utah. The study area encompasses five community types: pinyon-juniper, sagebrush, shadscale, blackbrush, creosote bush. The general distribution of these community types can be correlated directly with topography (see Results). METHODS. Vegetational analyses and small mammal studies were conducted at each sampling area during February, April, and August 1975. Vegetational sampling was designed to determine plant associations and dominant plant species at each site. Since the main goal was to determine small mammal occurrence along the transect, the three sampling periods were pooled for further analysis. Trees and shrubs were sampled using the point-centered quarter method of Cottam and Curtis (1956). Annual and perennial herbaceous vegetation was sampled using 25 0.9 m by 0.9 m quadrats placed at 3-m intervals along five parallel 15-m tape lines spaced 20 paces apart. Canopy-coverage for herbaceous vegetation was estimated for each species present in the quadrant. These estimates were made according to six cover classes: 0 5, 5 25, 25 50, 75 95, and 95 100%. An average cover value was calculated using the midpoint percentage value of each covering class. Estimates of percent cover of herbaceous plants and density/hectare were calculated for all stations except station 7, where the relative density of plant species and total cover were calculated. This content downloaded from 157.55.39.32 on Mon, 10 Oct 2016 04:24:32 UTC All use subject to http://about.jstor.org/terms The Southwestern Naturalist