The effect of beta-richness on fine particulate organic matter export through interspecific interactions in artificial stream networks

The role of biodiversity in regulating function in spatially complex environments has rarely been tested, but such tests are necessary to extrapolate diversity-function theory to natural systems. Using replicate artificial streams I tested the role of diversity of shredding caddisflies (Pycnopsyche guttifer and Lepidostoma sp.) among two upstream reaches on total decomposition, particle export, and the growth of filtering caddisflies (Hydropsyche betteni and Hydropsyche morosa) in a downstream reach. There were 3 factors: arrangement of shredders among two upstream reaches, leaf species (senesced or green speckled alder), and the presence or absence of filtering caddisflies. At 4 day intervals fine particles were collected from downstream collection filters and the total quantity (g), size spectra, and C/N of particles in 3 size classes (63-125, 125-250, 250-500 µm) were measured. Filterer growth and leaf mass loss over the course of the experiment were also recorded. Interactions between P.guttifer and L. sp were filmed and analyzed to determine how interspecific interactions affected feeding behavior. The results indicate that negative interactions between the two shredders slow the decomposition of senesced but not green speckled alder leaves. Slowed decomposition negatively impacts particle export. These results indicate that the spatial arrangement of shredders in stream networks could impact total network processing and downstream production, but that such effects are context dependent. These results indicate that we cannot scale up the results of simple diversity-function experiments without considering the role of space and context dependent interactions on ecosystem functioning.