Contrasting effects of salamanders on forest-floor macro- and mesofauna in laboratory microcosms

We employed laboratory microcosms to test the hypothesis that predation by the salamander, Plethodon cinereus, alters invertebrate species composition of a terrestrial detritus-based food web and thereby influences leaf-litter decomposition rates. We comparedh litter invertebrates among samples of leaf-litter substrate samples in microcosms either with or without individual salamanders. We used mesh leaf-litter bags to quantify leaf-litter decomposition and temporal changes in invertebrate abundance and community composition during colonization of new litter by invertebrates. We report that substrates within microcosms with P. cinereus had more podomorphic Collembola, fewer enchytraeid worms and fewer macroinvertebrate detritivores than controls at the end of the 3 month experiment. Total invertebrate density, and densities of podomorphic Collembola and Acari increased more rapidly in litter bags within salamander microcosms than in controls. In contrast, entomobryid Collembola were fewer in litter bags in salamander microcosms in comparison to controls. However, salamanders had no effect on leaf-litter decomposition rates. We hypothesize that salamander predation enhanced microbi-detritivore mesofauna densities by (1) reducing numbers of larger detritivores that compete with mesofauna, and/or by (2) providing a subsidy in the form of salamander feces that promoted growth of microflora. Further, we hypothesize that increases of mesofauna in salamander microcosms compensated for effects on litter decomposition that may have resulted from reductions in detritivorous macrofauna.