Effects of an Omnivorous Katydid,Salinity, and Nutrients on a Planthopper-<Emphasis Type="Italic">Spartina</Emphasis> Food Web |
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| Authors: | Juan M Jiménez Kazimierz Wi?ski Laurie B Marczak Chuan-Kai Ho Steven C Pennings |
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| Institution: | (1) Department of Biology and Biochemistry, University of Houston, Houston, TX 77204-5001, USA;(2) Present address: Department of Ecosystem and Conservation Sciences, College of Forestry and Conservation, University of Montana, Missoula, MT 59812, USA;(3) Present address: Institute of Ecology and Evolutionary Biology, National Taiwan University 1, Sec. 4, Roosevelt Rd., Taipei, 106, Taiwan, Republic of China; |
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| Abstract: | 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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