PARENT SESSION
Tuesday, August 8, 8:00-11:30 am
COS 20 - Food webs I: trophic interactions
Mississippi, Mezzanine Level, Cook Convention Center
Presiders: D Gruner
More than muck munchers: detritivores mediate predator-herbivore interactions.
Hines, Jes*,1, Denno, Robert1, 1 Department of Entomology, College Park, MD
ABSTRACT- Although it is widely recognized that primary production and decomposition are necessarily linked, there has been little investigation into the nature of interactions between primary producer and decomposer-based food webs. In the salt marsh system, predatory spiders such as Pardosa littoralis aggregate in areas rich in leaf litter-detritus. Therefore detritivores living in leaf litter have the potential to enhance predator populations by serving as a food resource. In contrast, if detritivores are able to rapidly consume leaf litter, the preferred habitat of predatory spiders, the presence of detritivores may preclude an abundance of spiders. In a factorial combination of mesocosms containing the salt marsh cord grass Spartina alterniflora, we manipulated the presence and absence of leaf litter, herbivores, detritivores, and predators. We measured how changes in interaction strength between these factors altered the ability of spiders to exert top-down control on detritivores and herbivores and examined cascading effects on decomposition. Detritivores with strong effects on decomposition such as the salt marsh isopod, Philoscia vittata, were less vulnerable to predation than amphipods such as Orchestia grillus, which had relatively reduced effects on decomposition. Both detritivores were consumed by Pardosa spiders even in the presence of a dominant salt marsh herbivore Prokelisia dolus. Decomposition rates were enhanced by the presence of detritivores and reduced in the presence of spiders, an effect that was dampened in the presence of herbivores. These results emphasize that the strength and consistency of predator-detritivore interactions can mediate interactions between predators and herbivores feeding on live plant material.
Key words: trophic dynamics, decomposers, interaction strength