No abstract

/ Prairie dogs (Cynomys spp.) have been labeled as keystone species because of their influence on biological diversity and ecosystem function. However, the validity of several assumptions used to support keystone status is questionable. We review the strength of the evidence and the magnitude of the prairie dog's effects on ecosystem structure and function. We use this review to reevaluate the keystone role for prairie dogs. Our goal is to encourage sound management of the prairie dog ecosystem by improving the ecological foundation of their keystone status. Our review confirms that prairie dogs affect a number of ecosystem-level functions but that their influence on prairie vertebrates may be less than previously suggested. Species richness and abundance patterns were variable among plants, mammals, and birds and were not consistently higher on prairie dog colonies compared to uncolonized areas. In addition, only nine of the 208 species listed in the literature as observed on or near prairie dogs colonies had quantitative evidence of dependence on prairie dogs. Abundance data indicated opportunistic use of colonies for an additional 20 species. A total of 117 species may have some relationship with prairie dogs, but we lacked sufficient data to evaluate the strength of this relationship. The remaining 62 species may be accidental or alien to the system. Despite our conclusion that some prairie dog functions may be smaller than previously assumed, collectively these functions are quite large compared to other herbivores in the system. We suggest that prairie dogs also provide some unique functions not duplicated by any other species and that continued decline of prairie dogs may lead to a substantial erosion of biological diversity and landscape heterogeneity across prairie and shrub-steppe landscapes. Thus, we concur that keystone status for prairie dogs is appropriate and may aid conservation efforts that help protect species dependent on prairie dogs and support other important ecosystem functions.KEY WORDS: Prairie dogs; Cynomys spp.; Keystone species; Ecosystem functions; Biological diversityhttp://link.springer-ny.com/link/service/journals/00267/bibs/24n2p177.html

Combined grazing by black-tailed prairie dogs (Cynomys Idovidanus) and bison (Bison b&on) produces and maintains a series of changes in the vegetation of prairie dog colonies. However, because their grazing patterns differ in frequency and intensity through time, their individual impacts may be different. The objective of this study was to determine the individual and combined Influences of these 2 herbivores in maintaining selected vegetation characteristics of a prairie dog colony in a mixed-grass prairie at Wind Cave National Park, S.D. This was assessed by monitoring plant responses during 2 years following exclusion from grazing by 1 or both species. In spite of their different grazing patterns, prairie dogs and bison had similar and independent (i.e., additive) effects in maintaining plant community structure. For example, total above ground biomass increased 32-36s within 2 years of removal of each species, primarily as a result of increases in accumulation of graminoid biomass. Plant species diversity, equitability, and dominance concentration were similar in all treatments both years, although there were slight decreases in relative abundance of forbs and increases in relative abundance of graminoids in the second year after removal of grazers. Mean graminoid leaf nitrogen concentration (May to September) declined slightly but significantly after removal of prairie dogs (1.49 to 1.3896) in 1985, and after bison exclusion (1.64 to 1.50%) in 19ll6. We suggest that rate of vegetation change following removal of grazers depends upon weather conditions, plant species composition, and prior intensity and duration of grazing.

ABSTRACT. 1. Patterns of daily and seasonal activity for seven species of tenebrionid beetles, genus Eleodes, were investigated in the shortgrass prairie of northeastern Colorado. The relationship between time of activity, body temperatures, and rates of water loss of the beetles was examined in the field and in laboratory experiments. 2. Common species were active from April until the end of October; however, asynchronous peaks of abundance occurred. 3. Beetles were diurnally active with peaks of daily activity occurring 2–4 h after sunrise and before sunset. Less than a 2 h shift in mean time of activity occurred between seasons. 4. Within species, body temperatures measured in the field closely corresponded to temperatures selected in an experimental thermal gradient; hence, species seemed to prefer particular body temperatures and were most active during times when those temperatures could be achieved. Body temperatures measured in the field approximated ambient temperatures measured in the vicinity of the beetle. 5. Significant differences among several species were found for times of daily activity and corresponding body temperatures. 6. Ability to resist water loss by evaporation was not correlated with daily or seasonal activity patterns.

Morphologically distinct populations of a North American perennial grass, Agropyron smithii, collected from a heavily grazed prairie dog (Cynomys ludovicianus) colony (PDC) and a grazing exclosure (EX), were grown in an environmental chamber to determine whether: (1) leaf silicon (Si) concentrations are greater in plant populations which differentiated under heavy grazing pressure, and (2) leaf silicification is inducible by defoliation. Mean shoot Si concentration of nondefoliated plants was greater in the PDC population (2.2%) than the EX population (1.9%) over the 18 wk experiment, largely as a result of differences in Si concentrations in leaf blades. However, leaf Si concentration was lower in defoliated plants of each population than in nondefoliated plants, indicating that leaf silicification was not an inducible herbivore defense mechanism in A. smithii. The higher leaf Si concentrations from the heavily grazed population may be associated with grazingrelated environmental stresses such as a warmer, drier microclimate or with morphological characteristics related to grazing tolerance or avoidance.