Consequences of climatic variability and land-management change for mammals in a working Great Plains landscape

Background/Question/Methods Semiarid grasslands such as shortgrass steppe embody the working landscape, with livestock grazing performing the ecological roles of large mammalian herbivores that once roamed these grasslands. At the northern limit of shortgrass steppe in north-central Colorado, variability in the timing and amount of precipitation influences plant productivity and diversity, which in turn determine the availability of resources and biotic interactions for consumers such as small mammals. Many of these species depend on vegetative cover and the abundance of arthropods and seeds as food, and thus are likely to be sensitive to changes to precipitation and grazing. Ecosystem engineers, such as prairie dogs and pocket gophers, provide habitat for other species and are a key source of small-scale disturbance that alters plant diversity. The expansion and contraction of prairie dog colonies in response to climatic variability and an invasive disease, plague, in particular pose significant challenges to land management because of the potential for competition with livestock and because of the recognized conservation importance of prairie dogs. We took advantage of 15 years of small mammal population monitoring and experimental studies of grazing effects and prairie dogs associated with the Shortgrass Steppe Long-Term Ecological Research project to explore the possible consequences of changes in climate and land use for mammal populations in shortgrass steppe. 

Results/Conclusions Changes in small mammal populations over the past 15 years suggest strong and persistent responses to climatic variability. We observed a marked shift in rodent species composition in favor of more arid-adapted granivores following a prolonged drought in the early 2000s. The abundance of black-tailed jackrabbits and acreage of prairie dog colonies also increased over this period, while coverage of gopher mounds declined. Regional increases in prairie dog acreage occurred within the context of local extinction-colonization events of colonies in response to plague, resulting in an increase in the number and connectivity of colonies but a decrease in mean size. Vegetation in colonies responded quickly to extinction of prairie dogs, while responses of consumers were more variable and lagged behind those of plants. Small mammal communities were sensitive to long-term removal of grazing, perhaps reflecting the close proximity of our study site to northern mixed prairie, and to the availability of burrows and mounds associated with prairie dogs and gophers. We discuss ongoing and new experiments designed to investigate the interactions between climate and land-use practices, including grazing, fire and prairie dog management.