Bottom‐up when it is not top‐down: Predators and plants control biomass of grassland arthropods. Issue 5 (19th March 2020)

• Record Type: Journal Article
• Authors: Welti, Ellen A. R.; Prather, Rebecca M.; Sanders, Nathan J.; de Beurs, Kirsten M.; Kaspari, Michael
• Editors: Morris, Rebecca
• Is Part Of: Journal of animal ecology. Volume 89:Issue 5(2020)
• Page Start: 1286
• Page End: 1294
• Publication Date: 2020-03-19
• Subjects: biomass -- Exploitation Ecosystem Hypothesis -- grasshopper -- insect -- katydid -- leafhopper -- prairie -- spider; Animal ecology -- Periodicals; 591.7
• DOI: 10.1111/1365-2656.13191
• Languages: English
• ISSNs: 0021-8790

Abstract

Abstract: We investigate where bottom‐up and top‐down control regulates ecological communities as a mechanism linking ecological gradients to the geography of consumer abundance and biomass. We use standardized surveys of 54 North American grasslands to test alternate hypotheses predicting 100‐fold shifts in the biomass of four common grassland arthropod taxa—Auchenorrhyncha, sucking herbivores, Acrididae, chewing herbivores, Tettigoniidae, omnivores, and Araneae, predators. Bottom‐up models predict that consumer biomass tracks plant quantity (e.g. productivity and standing biomass) and quality (nutrient content) and that ectotherm access to food increases with temperature. Each of the focal trophic groups responded differently to these drivers: the biomass of sucking herbivores and omnivores increased with plant biomass; that of chewing herbivores tracked plant quality; and predator biomass did not depend on plant quality, plant quantity or temperature. The Exploitation Ecosystem Hypothesis is a top‐down hypothesis that predicts a shift from resource limitation of herbivores when plant production is low, to predator limitation when plant production is high. In grasslands where spider biomass was low, herbivore biomass increased with plant biomass, whereas bottom‐up structuring was not evident when spiders were abundant. Furthermore, neither predator biomass nor trophic position (via stable isotope analysis) increased with plant biomass, suggesting predators themselves are top‐down limited. Stable isotope analysis revealed that trophic position of the chewing herbivore and omnivore increased significantly with plant biomass, suggesting these groups increased scavenging and meat consumption in grasslands with higher carbohydrate availability. Taken together, our snapshot sampling documents gradients of food web structure across 54 grasslands, consistent with multiple hypotheses of bottom‐up and top‐down regulation. Abstract : The authors asked how biomass and trophic position of four major grassland arthropod taxa shift across 54 North American grasslands, sites spanning gradients of climate, nutrient availability and plant productivity. The results find support for both bottom‐up and top‐down processes governing the amount of consumer biomass a grassland can sustain.