Direct and indirect effects of an ecosystem engineer on a shrubland-prairie food web

Authors: DUCHARDT, COURTNEY - University Of Wyoming; Porensky, Lauren; PEARSE, IAN - Us Geological Survey (USGS)

Submitted to: Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2020
Publication Date: 1/12/2021
Citation: Duchardt, C., Porensky, L.M., Pearse, I.S. 2021. Direct and indirect effects of an ecosystem engineer on a shrubland-prairie food web. Ecology. 102(1). Article e03195. https://doi.org/10.1002/ecy.3195.
DOI: https://doi.org/10.1002/ecy.3195

Interpretive Summary: A species that directly alters the surrounding habitat in a way that affects other species is termed an "ecosystem engineer", and these species are often identified as conservation targets. There is evidence that black-tailed prairie dogs are important ecosystem engineers in the Great Plains, and that they are associated with higher wildlife diversity. However, there are many ways prairie dogs can affect different species (e.g., as a prey resource, or in changing the structure of habitat), and most studies do not directly investigate which aspects of prairie dogs affect other species. We collected data on vegetation, arthropods and birds to determine if and how prairie dogs affect these different groups. We found that prairie dogs decrease the cover of shrubs and vegetation, and that shrub-nesting birds decrease in response to this reduction. At the same time, other bird species are directly and positively correlated with the density of prairie dogs. This indicates that management that mimics prairie dog disturbance may not be adequate, and that having prairie dogs in the landscape is necessary for certain species.

Technical Abstract: Keystone engineers are critical drivers of biodiversity throughout ecosystems worldwide. Within the North American Great Plains, the black-tailed prairie dog is an imperiled ecosystem engineer and keystone species with well-documented impacts on the flora and fauna of rangeland systems. However, because this species affects ecosystem structure and function in myriad ways (i.e., as a consumer, a prey resource, and a disturbance vector), it is unclear which effects are most impactful for any given prairie-dog associate. We applied Structural Equation Models (SEM) to disentangle direct and indirect effects of prairie dogs on multiple trophic levels (vegetation, arthropods, and birds) in the Thunder Basin National Grassland. Arthropods did not show any direct response to prairie dog occupation, but multiple bird species and vegetation parameters were directly affected. Surprisingly, the direct impact of prairie dogs on colony-associated avifauna (horned lark [Eremophila alpestris] and mountain plover [Charadrius montanus]) had greater support than a mediated effect via vegetation structure, indicating that prairie dog disturbance may be greater than the sum of its parts in terms of impacts on localized vegetation structure. Overall, our models point to a combination of direct and indirect impacts of prairie dogs on associated vegetation, arthropods, and avifauna.