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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Effects of an Omnivorous Katydid, Salinity, and Nutrients on a Planthopper-Spartina Food Web
Auteurs :	Juan M. Jimenez, Auteur ; Kazimierz Wieski, Auteur ; Laurie B. Marczak, Auteur ; Chuan-Kai Ho, Auteur ; Steven C. Pennings, Auteur
Type de document :	Article
Dans :	Estuaries and Coasts (35(2) MAR 2012)
Article en page(s) :	475-485
Résumé :	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.

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