Competition and facilitation between a native and a domestic herbivore: trade‐offs between forage quantity and quality

Abstract

Potential competition between native and domestic herbivores is a major consideration influencing the management and conservation of native herbivores in rangeland ecosystems. In grasslands of the North American Great Plains, black-tailed prairie dogs (Cynomys ludovicianus) are widely viewed as competitors with cattle but are also important for biodiversity conservation due to their role in creating habitat for other native species. We examined spatiotemporal variation in prairie dog effects on growing-season forage quality and quantity using measurements from three colony complexes in Colorado and South Dakota and from a previous study of a fourth complex in Montana. At two complexes experiencing below-average precipitation, forage availability both on and off colonies was so low (12-54 g/m2) that daily forage intake rates of cattle were likely constrained by instantaneous intake rates and daily foraging time. Under these dry conditions, prairie dogs (1) substantially reduced forage availability, thus further limiting cattle daily intake rates, and (2) had either no or a small positive effect on forage digestibility. Under such conditions, prairie dogs are likely to compete with cattle in direct proportion to their abundance. For two complexes experiencing above-average precipitation, forage quantity on and off colonies (77-208 g/m2) was sufficient for daily forage intake of cattle to be limited by digestion rather than instantaneous forage intake. At one complex where prairie dogs enhanced forage digestibility and [N] while having no effect on forage quantity, prairie dogs are predicted to facilitate cattle mass gains regardless of prairie dog abundance. At the second complex where prairie dogs enhanced digestibility and [N] but reduced forage quantity, effects on cattle can vary from competition to facilitation depending on prairie dog abundance. Our findings show that the high spatiotemporal variation in vegetation dynamics characteristic of semiarid grasslands is paralleled by variability in the magnitude of competition between native and domestic grazers. Competitive interactions evident during dry periods may be partially or wholly offset by facilitation during periods when forage digestibility is enhanced and forage quantity does not limit the daily intake rate of cattle.

Black-Tailed Prairie Dogs, Cattle, and the Conservation of North America’s Arid Grasslands

“…These patterns probably resulted from prairie dog activities during the grass growing season that enhance forage quality, such as removal of standing dead biomass and clipping of vegetation that increases plant nitrogen uptake, in addition to the lack of other more palatable forage options during the winter season [20,52]. …”

“…However, these ecological relationships between cattle and prairie dogs probably vary across the geographic ranges and different species of prairie dogs, and with variation in precipitation and plant productivity [52]. For example, in the mixed-grass prairie, cattle spend significantly more time in pastures with prairie dog colonies compared to pastures without colonies [39].…”

Successive sheep grazing reduces population density of Brandt’s voles in steppe grassland by altering food resources: a large manipulative experiment

“…Repeated grazing is often necessary for maintaining high levels of secondary compounds (Gustafson and Ryan 1976), because the responses of food quality to grazing may be delayed (Saetnan et al 2012). The response of forage nitrogen content and digestibility in plants to grazing may be positive (Augustine and Springer 2013) or neutral (Saetnan et al 2012). In our study, MG in August showed a positive effect on crude protein.…”

“…The food competition hypothesis has been proposed to explain population declines of small rodents under livestock grazing pressure in other studies (Augustine and Springer 2013). Consistent with this hypothesis, decreased forage quantity, reflected in lower plant cover and height, have been widely reported in grazed sites (Steen et al 2005;Torre et al 2007).…”

A Management Framework for the Transition from Livestock Production toward Biodiversity Conservation on Great Plains Rangelands

“…Cattle and bison exhibit considerable dietary overlap (Plumb andDodd 1993, Hartnett et al 2007) and therefore above relatively low population levels we expect their relationship to be competitive. Effects of prairie dogs on livestock production are complex and, depending on site conditions such as rainfall amounts, may be facilitative or competitive (Derner et al 2006, Augustine andSpringer 2013). When competitive, the cost of prairie dog control may exceed reduced revenues from livestock production (Breland et al n.d.).…”