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

Abstract

The importance of cascading effects of grasshopper predators on plant biomass involving grasshoppers in grassland ecosystems appears variable. A constraint of most grasshopper trophic cascade studies to date is that they examine responses of a single grasshopper species, while grasshopper feeding guilds could affect whether a trophic cascade is observed. As grasslands are grass dominated, grass feeding grasshoppers generally have stronger impacts on plant biomass than mixed grass and forb feeding species indicating that trophic cascades should be observed more commonly with grass feeding species. Grasshopper feeding preference could have important implications for predicting the outcome of grasshopper predator-prey interactions. I conducted similar experiments in two years with different grasshopper feeding guilds, grass feeding and mixed grass and forb feeding, to examine the importance of cascading predator effects at a grass dominated 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.