Population Ecology of Uinta Ground Squirrels

The behavior and ecology of Uinta ground squirrels (Spermophilus armatus) at the Utah State University Forestry Field Station northeast of Logan, Utah were studied from 1964-1971 to determine the role of behavior in population regulation. From 1965 to 1968, data were collected to establish population norms. In 1968, the population density was reduced experimentally to help elucidate regulatory processes. This paper compares the dynamics of the population before and after the population reduction. Before the density reduction, juvenile survival was lower than that of yearlings and adults. The disappearance of juveniles was associated with their tendency to disperse from the natal burrow while still small. The litter size of yearlings was smaller than that of adults. The principal changes following the reduction were an increase in percentage of yearling squirrels breeding and a decrease in dispersal of juveniles. Litter size and proportion of adult females breeding did not change significantly. Dispersal of squirrels from the study area was the principal regulatory factor. Losses during hibernation, presumably to badger predation, also decreased after the reduction. Several conclusions were drawn. The importance of anyone of the complex of factors, which determined the dynamics of the population, varied with place, time, and population density. The value of habitat was affected by population density as well as the physical environment. Density pressures seemed to have more effect on subordinate than on dominant squirrels. Surplus animals from the prime habitat raised the population density in the surrounding area. Dispersing animals probably suffered higher mortality than those which stayed, but this did not imply that dispersal was maladaptive for the individual. (58 pages