Ecosystem engineering varies spatially: A test of the vegetation modification paradigm for prairie dogs

Authors: BAKER, BRUCE - Retired Non ARS Employee; Augustine, David; SEDGWICK, JAMES - Retired Non ARS Employee; LUBOW, BRUCE - Colorado State University

Submitted to: Ecography
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2012
Publication Date: 4/4/2012
Citation: Baker, B., Augustine, D.J., Sedgwick, J.A., Lubow, B.C. 2012. Ecosystem engineering varies spatially: A test of the vegetation modification paradigm for prairie dogs. Ecography. 36(2):230-239.

Interpretive Summary: Prairie dogs can influence aboveground and belowground structure of grassland and shrubland ecosystems, but their effect on aboveground vegetation structure has primarily been studied at a single site in the northern mixed prairie of South Dakota, USA. We examined the degree to which prairie dogs decrease the height and volume of vegetation and the cover of grasses and tall shrubs, and increase the cover of bare ground and forbs across a broad region of western North America. We sampled vegetation on and off 279 colonies at 13 major complexes of three prairie dog species distributed across five ecoregions in Montana, South Dakota, Wyoming, Utah, Colorado, Kansas, Arizona and Mexico. We found consistent effects of black-tailed prairie dogs in northern mixed prairie of Montana, Wyoming and South Dakota, where visual obstruction (a surrogate for vegetation height and volume), grass cover, and tall shrub cover were lower, and bare ground and forb cover were higher, on colonies than at paired off-colony sites. Outside the northern mixed prairie, all prairie dog species consistently reduced visual obstruction, but their effects on cover of plant functional groups varied with prairie dog species and the grazing tolerance of dominant perennial grasses. White-tailed prairie dogs in sagebrush steppe of Wyoming and Utah did not reduce shrub cover, whereas black-tailed prairie dogs suppressed shrub cover at all complexes with tall shrubs in the surrounding vegetation matrix. Effects of black-tailed prairie dogs in shortgrass steppe of Colorado/Kansas were similar to effects of Gunnison’s prairie dogs in Arizona, which may reflect the dominance of grazing-tolerant shortgrass species at both complexes. Variation in vegetation modification by prairie dogs may be understood in terms of the responses of different dominant grass species to intense defoliation and differences in foraging behavior among prairie dog species. Regional variation in the effects of prairie dogs suggests spatial variation in their role as a keystone species in grasslands.

Technical Abstract: Prairie dogs (Cynomys spp.) can substantially modify aboveground and belowground structure of grassland and shrubland ecosystems, but generalizations about their engineering effect on aboveground vegetation structure are derived largely from intensive studies at a single site in the northern mixed prairie of South Dakota, USA. We tested the emergent paradigm that prairie dogs decrease the height and volume of vegetation and the cover of grasses and tall shrubs, and increase the cover of bare ground and forbs. We sampled vegetation on and off 279 colonies at 13 major complexes of three prairie dog species distributed across five ecoregions in North America (northern mixed prairie, sagebrush steppe, shortgrass steppe, Colorado Plateau grassland, and Chihuahuan desert grassland). The paradigm was generally supported at seven black-tailed prairie dog (C. lucovicianus) complexes in northern mixed prairie, where visual obstruction (a surrogate for vegetation height and volume), grass cover, and tall shrub cover were lower, and bare ground and forb cover were higher, on colonies than at paired off-colony sites. Outside the northern mixed prairie, all prairie dog species consistently reduced visual obstruction, but their effects on cover of plant functional groups varied with prairie dog species and the grazing tolerance of dominant perennial grasses. White-tailed prairie dogs (C. leucurus) in sagebrush steppe did not reduce shrub cover, whereas black-tailed prairie dogs suppressed shrub cover at all complexes with tall shrubs in the surrounding vegetation matrix. Effects of black-tailed prairie dogs in shortgrass steppe were similar to effects of Gunnison’s prairie dogs (C. gunnisoni) in Colorado Plateau grassland, which may reflect the dominance of grazing-tolerant shortgrass species at both complexes. Variation in vegetation modification may be understood in terms of the responses of different dominant perennial grasses to intense defoliation and differences in foraging behavior among prairie dog species. Spatial variation in the engineering effects of prairie dogs suggests spatial variation in their keystone role, and that engineering by other burrowing herbivores may vary across broad geographic regions.