Juan M. JiménezKazimierz WięskiLaurie B. MarczakCHUAN-KAI HOSteven C. Pennings2018-09-102018-09-102012http://www.scopus.com/inward/record.url?eid=2-s2.0-84857657878&partnerID=MN8TOARShttp://scholars.lib.ntu.edu.tw/handle/123456789/371058Top-down and bottom-up effects interact to structure communities, especially in salt marshes, which contain strong gradients in bottom-up drivers such as salinity and nutrients. How omnivorous consumers respond to variation in prey availability and plant quality is poorly understood. We used a mesocosm experiment to examine how salinity, nutrients, an omnivore (the katydid Orchelimum fidicinium) and an herbivore (the planthopper Prokelisia spp.) interacted to structure a simplified salt marsh food web based on the marsh grass Spartina alterniflora. Bottom-up effects were strong, with both salinity and nutrients decreasing leaf C/N and increasing Prokelisia abundance. Top-down effects on plants were also strong, with both the herbivore and the omnivore affecting S. alterniflora traits and growth, especially when nutrients or salt were added. In contrast, top-down control by Orchelimum of Prokelisia was independent of bottom-up conditions. Orchelimum grew best on a diet containing both Spartina and Prokelisia, and in contrast to a sympatric omnivorous crab, did not shift to an animal-based diet when prey were present, suggesting that it is constrained to consume a mixed diet. These results suggest that the trophic effects of omnivores depend on omnivore behavior, dietary constraints, and ability to suppress lower trophic levels, and that omnivorous katydids may play a previously unrecognized role in salt marsh food webs. © 2011 Coastal and Estuarine Research Federation.Omnivory; Orchelimum fidicinium; Prokelisia spp.; Salt marsh; Spartina alterniflora; Top-down and bottom-up interactions[SDGs]SDG14bottom-up control; crab; diet; food web; grass; insect; marine ecosystem; nutrient budget; omnivory; saltmarsh; sea surface salinity; sympatry; top-down control; trophic level; Animalia; Archaeorrhyncha; Decapoda (Crustacea); Hymenachne; Orchelimum; Orchelimum fidicinium; Prokelisia; Spartina; Spartina alterniflora; Tettigoniidaejournal article10.1007/s12237-011-9458-7