Mulder and Ruess investigated the direct and indirect effects of herbivory by Brant geese (Branta bernicla nigricans) on Triglochin palustris (arrowgrass), in a subarctic salt marsh in southwestern Alaska. When the authors examined the results from the clipping and grazing experiments only, they were tempted to conclude that the overall effect of geese on arrowgrass is negative, due in part to increased feces deposition, and arrowgrass is outcompeted for light by its neighbors. Nevertheless, the gosling experiment suggests that the presence of other species also can have a positive effect on arrowgrass. The authors cannot predict the net result of these opposing effects; however, they demonstrate that, in examining the effect of herbivory on a plant in the context of a community, we need to focus not just on the plant, but also on feedback from the community to the herbivore, through changes in forage plant size, forage quality, and species composition.
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