Effects of grasshoppers on prairies: Herbivore composition matters more than richness in three grassland ecosystems

Authors: LAWS, ANGELA - University Of Houston; PRATHER, CHELSE - University Of Houston; Branson, David - Dave; PENNINGS, STEVEN - University Of Houston

Submitted to: Journal of Animal Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2018
Publication Date: 9/10/2018
Publication URL: http://handle.nal.usda.gov/10113/6152997
Citation: Laws, A.N., Prather, C.M., Branson, D.H., Pennings, S. 2018. Effects of grasshoppers on prairies: Herbivore composition matters more than richness in three grassland ecosystems. Journal of Animal Ecology. 87(6):1727–1737. https://doi.org/10.1111/1365-2656.12897.
DOI: https://doi.org/10.1111/1365-2656.12897

Interpretive Summary: In grassland ecosystems, grasshoppers are common and important herbivores. However, we do not understand the role orthopteran diversity plays in ecosystem function nor how the role of grasshoppers might vary among rangeland sites. Some grasshoppers feed exclusively on grasses, some exclusively on forbs, while others feed on a mixed diet of grasses and forbs. By using different combinations of orthopteran species in field mesocosms, examine effects of functional richness, species richness, and species identity on grassland processes using parallel field experiments in three grassland sites in Montana, Kansas, and Texas. Using field cages to manipulate orthopteran functional and species richness, we tested if grasshopper feeding mode would be more important than species richness in determining detrimental effects of grasshoppers rangeland production. Results were qualitatively similar across all three grassland ecosystems. This generality despite the tremendous differences among the sites is both striking and encouraging, because it suggests that it will be possible to generalize about grasshopper community effects widely among grasslands. Grasshoppers play important roles in many ecosystems and future studies should consider effects on these additional functions to assist managers in deciding when grasshopper control efforts are warranted to protect rangeland.

Technical Abstract: Understanding how biodiversity affects ecosystem functioning is a key question in ecology. Previous research has found that plant diversity often enhances many ecosystem processes, but less is known about the role of consumer diversity to ecosystem processes, especially in terrestrial ecosystems. Furthermore, we do not know how general biodiversity responses are among sites. Here, we examined the role of insect herbivore (Orthoptera) diversity on plant production using parallel field experiments in three grassland sites located in Texas, Kansas, and Montana, USA. Using mesocosms, we independently manipulated herbivore species richness, functional richness (functional feeding group), and functional composition. Diversity treatments were maintained throughout the experiment by replacing dead individuals. Plant biomass was destructively sampled at the end of the experiment. We found no effect of species richness or functional richness on plant biomass. However, herbivore functional composition was important. Treatments with grass feeding species only reduced plant biomass more than treatments with mixed feeding species only and treatments with mixed and grass feeding species together. Our experiments were conducted in three grassland types that differed in abiotic conditions, plant community and orthopteran community composition. Despite these differences among sites, patterns in plant responses to diversity treatments were consistent among sites, indicating that this finding is robust among grasslands.