Effects of an Omnivorous Katydid, Salinity, and Nutrients on a Planthopper-Spartina Food Web

• Published in: Estuaries and coasts 2012-03, Vol.35 (2), p.475-485
• Main Authors: Jiménez, Juan M., Więski, Kazimierz, Marczak, Laurie B., Ho, Chuan-Kai, Pennings, Steven C.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal populations; Animal, plant and microbial ecology; Aquatic ecology; Aquatic plants; Biological and medical sciences; Brackish water ecosystems; Coastal Sciences; Coasts; Decapoda; Diet; Earth and Environmental Science; Ecology; Environment; Environmental Management; Estuaries; Food chains; Food webs; Freshwater & Marine Ecology; Fundamental and applied biological sciences. Psychology; Grasses; Herbivores; Insects; Nutrient nutrient interactions; Nutrients; Omnivores; Orchelimum; Orchelimum fidicinium; Plant nutrition; Plant populations; Plants; Prey; Prokelisia; Salinity; Salt marshes; Shellfish; Spartina alterniflora; Synecology; Tettigoniidae; Trophic levels; Water and Health; Wetland ecology
• ISSN: 1559-2723; 1559-2731
• DOI: 10.1007/s12237-011-9458-7

Top-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.