D3054: The effects of experimental subsidies on leaf litter arthropod communities

Spatial subsidies are the asymmetric movement of resources from a donor habitat to a distinct recipient habitat. Arthropod rain, i.e., the fall of arthropods from tree crowns to the forest understory, is a potentially important subsidy link between canopy food webs and detritus-based litter food webs. We added homogenized fragments of Blaptica dubia cockroaches in high (12g m-2) and low (2g m-2) concentrations to replicated quadrats of leaf litter as a pulse subsidy in a temperate forest. Controls were: 1) zero subsidy and 2) addition of foam pellets in place of cockroach fragments. Litter in each quadrat was subsampled 2, 5, 10, and 20 days post-treatment. Arthropods were extracted from the litter with Berlese funnels and identified to morphospecies. We found 175 arthropod morphospecies in total. Mean richness and abundance declined over time in the 2g and control treatments, but showed no significant changes in the 12g and foam treatments. Collembola decreased in abundance but not richness, while oribatid mites increased in the 12g treatment. Spider, ant, and predatory mite responses were highly variable and inconsistent over time. These results suggest that pulse subsidies do not generate a consistent, conspicuous, bottom-up trophic cascade in litter. Understanding patterns of nutrient flow in forests is critical to predicting spatiotemporal patterns of biodiversity and ecosystem processes.