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The effects of grasshoppers on soil animal communities in the Shortgrass Steppe of northern Colorado




Post, Keith Harrison, author
Wall, Diana H., advisor
Knapp, Alan K., committee member
Kondratieff, Boris C., committee member
Ocheltree, Troy W., committee member

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A burgeoning area of research in ecology is on the linkages between aboveground and belowground components of terrestrial systems. Leaf-feeding insects can affect soil communities directly via frass deposition or indirectly through alterations in the quantity or composition of plant roots or the amount of labile carbon exuded belowground. These pathways can affect the three soil energy channels (i.e., root, soil bacterial, and soil fungal) by altering the absolute and/or relative amounts of their source materials and, in turn, impact soil microbial community composition and higher trophic levels, including soil nematodes and microarthropods. This aboveground-belowground interaction is important to fully understanding the functioning of terrestrial ecosystems, especially in the context of global climate change. This study investigated the effects of short-term grasshopper exclusion in the shortgrass steppe of northern Colorado on plant abundance and temporal changes in trophic groups of soil animals. Above- and belowground plant biomass, soil nematode, and soil microarthropod responses to altered grasshopper abundances were determined using grasshopper exclosures and caged controls from late summer–early fall 2014. Plant community composition during the study was drastically different than long-term data. Bouteloua gracilis, a co-dominant grass, was reduced to an average of 5.75% of total aboveground biomass, whereas the typically rare, annual grass Vulpia octoflora exploded to over 93%. Total above- and belowground plant biomass and aboveground biomass from V. octoflora and other grasses (mainly B. gracilis) were unaffected by grasshopper exclusion. Grasshopper feeding enhanced the ratio of bacterivorous to fungivorous nematodes, which remained similar through time in exclosures. Proportions of bacterial-feeding nematodes increased in caged controls but decreased in exclosures, while there was a trend for the opposite pattern for plant parasitic nematodes. Temporal changes in the densities of soil microarthropods, mites, and mite trophic groups were similar between cage types. Results indicate that grasshoppers enhanced the relative dominance of the soil bacterial energy channel, likely through greater frass deposition. Apparent exclosure effects on plant parasitic nematodes suggest a possible belowground plant response to altered grasshopper populations, which could have been weak because these effects were specific to the then-rare B. gracilis, which was about to enter senescence. Implications of this research in the context of global climate change, particularly droughts in the shortgrass steppe, are discussed.


Includes bibliographical references.
2015 Summer.

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shortgrass steppe
soil food web
soil fauna


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