Threshold responses of grassland and sagebrush birds to patterns of disturbance created by an ecosystem engineer

Authors: DUCHARDT, COURTNEY - University Of Wyoming; Augustine, David; BECK, JEFFREY - University Of Wyoming

Submitted to: Landscape Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2019
Publication Date: 4/2/2019
Citation: Duchardt, C.J., Augustine, D.J., Beck, J.L. 2019. Threshold responses of grassland and sagebrush birds to patterns of disturbance created by an ecosystem engineer. Landscape Ecology. 34(4):895-909. https://doi.org/10.1007/s10980-019-00813-y.
DOI: https://doi.org/10.1007/s10980-019-00813-y

Interpretive Summary: Black-tailed prairie dogs live in rangelands of the western Great Plains, and they often strongly influence their environment by digging burrows and intensively grazing on the vegetation. This intense grazing often alters the types of plants growing on prairie dog colonies, and maintains them in a short statured state. For this reason, prairie dogs are often referred to as “ecosystem engineers.” The effects that prairie dogs have on vegetation can also greatly alter habitat for other coexisting species, such as birds. Some previous research shows that prairie dogs may enhance habitat for one suite of birds while degrading habitat for others. We examined the influence of prairie dogs on coexisting birds in grassland-shrubland landscape in eastern Wyoming. We evaluated how birds associated with shortgrass, midgrass, and sagebrush (Artemisia spp.) plant communities respond to the size and distribution of prairie dog colonies, and identified thresholds where abundance changes. We surveyed bird abundance on prairie dog colonies of varying sizes and shapes, across colony edges into undisturbed habitat, and within undisturbed sagebrush in northeastern Wyoming. We modeled species responses to colony presence, distance to colony edge, and total area and edge density of colonies at four spatial scales (100 m, 225 m, 500 m, 1000 m radii from a given location). Sagebrush specialists like Brewer’s sparrow and sage thrasher were 4.5 times more abundant in undisturbed shrublands. In contrast, mountain plovers were abundant on colonies but showed a non-linear response to colony edge, increasing in abundance up to 600 m from edges then declining further towards the center of large colonies.

Technical Abstract: Context: Burrowing mammals play a role in rangeland disturbance worldwide, enhancing habitat for certain species while negatively affecting others. However, little is known concerning effects of disturbance spatial pattern on co-occuring fauna. In the North American Great Plains, colonial black-tailed prairie dogs (Cynomys ludovicianus) may enhance habitat for one suite of birds while degrading habitat for others. Objectives: We examined the influence of prairie dogs on birds in a mosaic grassland-shrubland landscape. We evaluated how birds associated with shortgrass, midgrass, and sagebrush (Artemisia spp.) plant communities respond to spatial pattern of prairie dog disturbance, and identified thresholds where abundance changes. Methods: We surveyed bird abundance on prairie dog colonies of varying sizes and shapes, across colony edges into undisturbed habitat, and within undisturbed sagebrush in northeastern Wyoming. We modeled species responses to colony presence, distance to colony edge, and total area and edge density of colonies at four spatial scales (100 m, 225 m, 500 m, 1000 m). Results: Sagebrush specialists like Brewer’s sparrow (Spizella breweri) and sage thrasher (Oreoscoptes montanus) were 4.5 times more abundant in undisturbed shrublands. Conversely, the shortgrass-specialist mountain plover (Charadrius montanus) was abundant on colonies but showed a non-linear response to colony edge, increasing in abundance up to 600 m from edges then declining further towards colony cores. Conclusions: While some species may be broadly intolerant to disturbance, disturbance-dependent birds can display a ”goldilocks syndrome” relative to disturbance size. As such, management for multiple species of conservation concern can be optimized relative to other goals by identifying thresholds associated with the effect of disturbance.