PARENT SESSION
Poster Session 33: Trohpic Structure
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Consequences of omnivory for trophic interactions: a case from salt marshes.
Ho, Chuan-Kai *,1, Pennings, Steven1, 1 University of Houston, Houston, TX
ABSTRACT- Omnivory is thought to weaken the strength of trophic interactions in food webs. To test this hypothesis, we examined top-down impacts of an omnivorous salt marsh crab, Armases cinereum. Armases consumes both the shrub Iva frutescens and its aphid herbivores. In a 2-year field experiment, Armases tended to reduce aphid populations (P=0.09), and significantly increased Iva leaf size and number. In the laboratory, Armases strongly suppressed aphid populations and released Iva from aphid damage, which was more serious than the direct damage to Iva caused by Armases. In this case, an omnivore had strong top-down effects leading to a trophic cascade. This result occurred because the top consumer, an omnivore, preferred to eat the herbivore over the plant whenever the herbivore was present in the system. Thus, when herbivores were abundant, Armases essentially functioned as a predator. When herbivores were rare, however, Armases was able to sustain itself in the system by feeding on plants. This pattern of feeding preferences is probably common for omnivores that feed on both herbivores and plants, and this kind of omnivore may therefore have different food web effects than omnivores that feed on multiple animal species (e.g., predators and herbivores).
Key words: omnivory, trophic cascade, top-down, salt marsh