Grasshopper feeding preference affects cascading effects of predators on plant biomass in a mixed-grass prairie

Authors: Branson, David - Dave

Submitted to: FOOD WEBS
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2022
Publication Date: 1/31/2022
Citation: Branson, D.H. 2022. Grasshopper feeding preference affects cascading effects of predators on plant biomass in a mixed-grass prairie. Food Webs. 31. Article e00224. https://doi.org/10.1016/j.fooweb.2022.e00224.
DOI: https://doi.org/10.1016/j.fooweb.2022.e00224

Interpretive Summary: In studies with grasshoppers, some rangeland sites consistently find increased plant availability when predators are present with grasshoppers, while others exhibit variability. Numerous grasshopper species exist at most rangeland sites, including species that feed on grasses or a mix of grasses and flowering plants. In this study, positive effects of spiders on grass biomass were only apparent with high densities of a grass feeding grasshopper in a higher production year, indicating for the first time that grasshopper feeding preferences impact the strength of trophic cascades in this grass dominated system. More complex experiments are needed in semi-arid grass dominated ecosystems to understand the importance of grasshopper plant preference on grassland function, but understanding impacts of predators on primary production has important implications for grasshopper management on rangeland.

Technical Abstract: The importance of cascading effects of predators on plant biomass involving grasshoppers appears variable in grassland ecosystems. A constraint of most grasshopper trophic cascade studies to date is that they examine responses of a single grasshopper species, but grasshopper feeding guilds could affect whether a trophic cascade is observed. Grass feeding grasshoppers have been shown to generally have stronger impacts on grass biomass than mixed grass and forb feeding species, indicating that trophic cascades would be predicted to be more commonly observed for grass feeding species than with mixed or forb feeding species in grass dominated grasslands. We conducted separate experiments with a grass feeding and a mixed grass and forb feeding grasshopper species to examine the importance of cascading predator effects at a grass dominated northern mixed prairie site. For both experiments, treatments consisted of invertebrate removal, herbivore only, and herbivore plus predator treatments. There was no indication of a trophic cascade with high densities of a mixed feeding grasshopper species in a year with lower biomass production. Although plant regrowth following herbivory can weaken the appearance of trophic cascades, a trophic cascade on grass biomass was evident with high densities of a grass feeding grasshopper during a year with higher biomass production. As a result, plant preference appears to impact the importance of cascading effects of predators on plant biomass in this system.