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Competition and facilitation between a native and domestic herbivore: Tradeoffs between forage quantity and quality

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Potential competition between native and domestic herbivores for forage 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 ludocivianus) are widely viewed as competitors with cattle, but are also important for biodiversity conservation due to their role as a keystone species influencing a wide range of native flora and fauna. We examined spatiotemporal variation in prairie dog effects on growing-season forage quality and quantity based on 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•m-2) 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 these 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•m-2) was sufficient for daily forage intake rates of cattle to be limited by digestion rather than instantaneous forage intake rates. 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 weight 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 degree of 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 that may be visibly evident during dry periods can be partially or wholly offset by facilitation during periods when forage quantity does not limit the daily intake rate of cattle and forage digestibility is enhanced on prairie dog colonies.
David J. Augustine , Tim L. Springer
Cynomys ludovicianus , agroecosystems , arid lands , atmospheric precipitation , biodiversity , cattle , digestibility , digestion , dry environmental conditions , ecological competition , fauna , feed intake , flora , grasslands , grazing , growing season , herbivores , indigenous species , keystone species , primary productivity , rangelands , semiarid zones , spatial variation , temporal variation , weight gain , wet environmental conditions , wildlife management , Colorado , Great Plains region , Montana , South Dakota
Ecological Applications 2013 v.23 no.4
Journal Articles, USDA Authors, Peer-Reviewed
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