The world's grassland ecosystems are shaped in part by a key functional group of social, burrowing, herbivorous mammals. Through herbivory and ecosystem engineering they create distinctive and important habitats for many other species, thereby increasing biodiversity and habitat heterogeneity across the landscape. They also help maintain grassland presence and serve as important prey for many predators. However, these burrowing mammals are facing myriad threats, which have caused marked decreases in populations of the best‐studied species, as well as cascading declines in dependent species and in grassland habitat. To prevent or mitigate such losses, we recommend that grasslands be managed to promote the compatibility of burrowing mammals with human activities. Here, we highlight the important and often overlooked ecological roles of these burrowing mammals, the threats they face, and future management efforts needed to enhance their populations and grassland ecosystems.

A mathematical analysis of the changes in plant relative growth rates necessary to increase aboveground production following grazing was conducted. The equation derived gives an isoline where production of a grazed and ungrazed plant will be the same. The equation has four variables (mean shoot relative growth rate, change in relative growth rate after grazing, grazing intensity, and recovery time) and may be analyzed graphically in a number of ways.Under certain conditions, small increases in shoot relative growth rate following grazing will lead to increased aboveground production. Under other conditions, very large increases in relative growth rate after grazing can occur without production being increased over that of ungrazed plants. Plants growing at nearly their maximum potential relative growth rate have little opportunity to respond positively to grazing and potentially can sustain less grazing than plants with growth rates far below maximum. Plants with high relative growth rates at the time of grazing require large increases in growth rate while slow growing plants require only small increases. High grazing intensities are least likely to increase production and high grazing frequencies require greater responses than infrequent grazing events.

Plant responses to herbivory and links to belowground nitrogen cycling were investigated at Wind Cave National Park, South Dakota. Laboratory estimates of net nitrogen mineralization were highest in soils from the more altered areas of prairie dog colonies (Cynomys ludovicianus) and lowest in the adjacent, lightly grazed, uncolonized grassland. The ratio of CO2: net nitrogen mineralized, as index of immobilization, was highest in the uncolonized grassland and lowest in the altered core areas. Soil moisture was an important modifier of in situ field estimates of net nitrogen mineralization. Root biomass, an important carbon source for decomposers in perennial grasslands, was lowest in the altered core area and highest in the adjacent uncolonised grassland. Decreased nitrogen immobilization and increased net nitrogen mineralization in the laboratory incubations likely resulted from decreased root carbon inputs in grazed areas, which limited carbon availability to decomposers. Such increases in plant—available nitrogen may partially explain the frequently reported grazing—induced increases in shoot nitrogen concentrations. These studies suggest that carbon allocation to roots is a key link determining nitrogen—cycling responses to herbivory.

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Global minimum temperatures ( T MIN ) are increasing faster than maximum temperatures, but the ecological consequences of this are largely unexplored. Long-term data sets from the shortgrass steppe were used to identify correlations between T MIN and several vegetation variables. This ecosystem is potentially sensitive to increases in T MIN . Most notably, increased spring T MIN was correlated with decreased net primary production by the dominant C 4 grass ( Bouteloua gracilis ) and with increased abundance and production by exotic and native C 3 forbs. Reductions in B. gracilis may make this system more vulnerable to invasion by exotic species and less tolerant of drought and grazing.

We explored how responses of two populations variable in grazing tolerance provide feedbacks to nutrient supply by controlling carbon supply to soil heterotrophs. The study focused on differences in production and carbon and nitrogen allocation patterns between the two populations. The grazing-tolerant population, or on-colony population, is found on intensively grazed prairie dog colonies, and a grazing-intolerant population, the off-colony population, is found in uncolonized grasslands. Equations describing the production and allocation responses to defoliation for the two ecotypes described were incorporated into CENTURY, a nutrientcycling simulation model. Simulations showed an increase in plant production that paralleled increases in net nitrogen mineralization. Production was greater with grazing and was maintained at higher grazing intensities for the on-colony than the off-colony population. Differences between the populations provided important controls over nitrogen losses. Feedbacks between plant responses to grazing and nitrogen cycling accounted for increased nitrogen availability with grazing. These feedbacks were more important determinants of ecosystem function than were fertilization effects of urine and feces deposition. The simulation results suggest that ecosystem function may be sensitive to physiological differences in population responses to periodic disturbances like herbivory.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. Field experiments were performed over two growing seasons to investigate the response of Schizachyrium scoparium (C4 photosynthetic pathway) and Poa pratensis (C3) to natural and simulated bison urine deposition in a northern, mixed prairie in South Dakota. We also assessed potential feedbacks of urine deposition on herbivore grazing by monitoring grass response to defoliation and herbivore grazing preference for vegetation occupying urine patches.Total aboveground biomass and root mass were higher and root:shoot ratios were lower on urine patches than in the surrounding plant community. Higher total aboveground biomass on urine patches resulted primarily from increased aboveground P. pratensis production. Urine deposition in May had little effect on aboveground production of S. scoparium except during July when S. scoparium was most active. Urine deposition date and plant phenology appear important in determining changes in species composition. Following urine deposition, aboveground N concentrations of P. pratensis and S. scoparium were higher on patches relative to conspecifics off patches. This increase in N concentration following urine deposition was greater in P. pratensis. We suggest the large increase in P. pratensis biomass following urine deposition is related to its relatively large response to increased soil N availability and its rhizomatous habit. Root N concentrations were higher on urine patches. Poa pratensis on urine patches initiated growth earlier in the season and postponed senescence relative to plants off patches. Aboveground production following clipping was greater on urine patches and N concentrations in regrowth of both species were higher than concentrations in plants not previously clipped.Aboveground herbivore utilization was greater on urine patches than on adjacent vegetation. Although urine patches covered only 2% of the study site, they provided 7% of the biomass and 14% of the N consumed by aboveground herbivores from June through August. Urine patches probably provided an even greater source of forage and N for herbivores earlier and later in the growing season when surrounding vegetation was mostly quiescent.

Photosynthesis and regrowth were compared over a 10-day period following defoliation of about 75% of the tillers of western wheatgrass (Agropyron smithii) plants collected from a black-tailed prairie dog (Cynomys ludovicianus) town and a grazing exclosure at Wind Cave National Park, South Dakota. Prior to defoliation, dog town plants had more tillers, but fewer leaves per tiller, shorter and narrower leaf blades, more horizontal leaves, and higher leaf blade/leaf sheath ratios than plants from the grazing exclosure. Rates of net photosynthesis (P) did not differ significantly among plants of the two populations, either prior to or following defoliation. From Days 2-10 following defoliation, P of remaining undamaged leaves averaged 104% of predefoliation rates while P of similar leaves on non-defoliated plants declined steadily with time. averaging only 79% predefoliation rates during this period. Following defoliation, transpiration rates followed similar trends to CO exchange, and rates did not differ between plants of the two populations. Absolute rates of leaf elongation and shoot production were greater in plants from the exclosure. However, defoliation of plants from the exclosure population resulted in a 20% reduction in their cumulative shoot dry weight, while cumulative shoot dry weight of plants from the prairie dog town was not significantly affected by defoliation. This apparent ability of plants from the prairie dog town population to withstand defoliation better than plants from the exclosure was atributed to factors such as the higher leaf blade/leaf sheath ratio and more horizontal leaf angles of plants from the former population.