Predator/Prey-Interactions Promote Decomposition of Low-Quality Detritus
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Predation on detritivores is expected to decelerate detritivore-mediated decomposition processes. In field mesocosms, we studied whether the decomposition of leaf and needle litter of live oak (Quercus virginiana) and loblolly pine (Pinus taeda), respectively, was affected by saltmarsh detritivores (Gastropoda: Littoraria irrorata and Melampus bidentatus) and predacious omnivores (Decapoda: Armases cinereum) and their interactions. Both crabs and snails alone increased decomposition (mass loss) rates of oak litter, while a combination of both resulted in the same mass loss as in animal-free controls, probably due to crabs feeding on snails rather than litter. Neither crabs nor snails alone affected mass loss of pine litter, but a combination of both significantly increased decomposition rates. Irrespective of the litter type, crabs significantly increased mortality of the snails but gained biomass only on pine litter and only when detritivorous snails were present. Our findings suggest that unidirectional facilitation of omnivorous semi-terrestrial crabs by their detritivorous prey (saltmarsh snails) promotes the decomposition of low-quality (pine) litter. On high-quality (oak) litter, by contrast, negative effects of the predator prevail, resulting in a drop of decomposition rates when crabs were present, probably owing to predation on detritivorous snails. Thus, the effects of predator/prey-interactions on decomposition processes are context-dependent and are controlled by resource quality.
KeywordsDecomposition processes Predator/prey-interaction Omnivory Saltmarsh Spatial subsidy
Experiments described herein comply with the current laws of the U.S.A. and were conducted in conformity with the “Guiding principles in the care and use of animals” approved by the Council of the American Physiological Society. AB and CE were financially supported through grants from the Christian-Albrechts-Universität zu Kiel. Franziska Seer, Gregor Putze and Yury Zablotski provided invaluable assistance at all stages of the field work. We thank the U.S. National Science Foundation (OCE06-20959) for financial support. This is contribution number 1017 of the University of Georgia Marine Institute. This work is a contribution of the Georgia Coastal Ecosystems LTER program.
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