OOS 44-7 - Comparing aquatic and terrestrial top-down forces on a single intertidal plant

Thursday, August 11, 2011: 3:40 PM
15, Austin Convention Center
Steven Pennings, Biology and Biochemistry, University of Houston, Houston, TX and Brian R. Silliman, Department of Zoology, University of Florida, Gainesville, FL

The grass, Spartina alterniflora, which is the dominant angiosperm in salt marshes along the Atlantic and Gulf Coasts of the United States, is consumed by herbivores of both terrestrial (insects, mammals, birds) and marine (snails, crabs) origins.  Which of these herbivory pathways has the strongest impact on plant productivity?  Most studies have examined one pathway or the other, but not both together. We compiled and synthesized the results of experimental studies that excluded herbivores in the field to assess the relative importance of terrestrial versus marine herbivores on Spartina alterniflora productivity.


Studies of terrestrial herbivores were mostly done in the mid-Atlantic; studies of marine herbivores were mostly done in the south Atlantic.  Studies of sap-sucking insects and fungal-farming snails were the most common; studies of grasshoppers, vertebrates, and crabs were rare.  Both terrestrial and marine herbivores were capable of substantially reducing the biomass of Spartina.  Effects increased with herbivore density, in fertilized plots, and at low latitudes, and varied with abiotic conditions experienced by Spartina.  Because the herbivore community varies spatially in composition and density, either terrestrial or marine herbivores can dominate the food web at any particular site, and the data are inadequate for scaling up to the entire coastline.  A rigorous assessment of herbivore impacts requires an understanding of spatial variation in herbivore densities, an understanding of how herbivore behavior mediates herbivore density, an understanding of abiotic context, and an experimental approach.

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