Several studies in the past decade have shown that rates of ecosystem processes may be affected by the number of species involved in the processes. However, how products, such as frass and feces, that are derived from those processes indirectly affect other functional feeding groups (FFGs) and whether such effects vary with species number are not well understood. We manipulated presence/absence and species richness of shredding larval stoneflies in laboratory microcosms containing leaf litter to test whether the number of species affected the growth of suspension-feeding black fly larvae. The presence of shredders increased the production of particles (>0.1 mm) and contributed to 30 to 56% higher black fly growth than in the absence of shredders. In addition, species richness and composition of shredders significantly affected black fly growth. Thus, our results show that species richness and composition in one FFG may affect FFGs further down the processing chain, most likely via effects on both quantity and size distribution of products derived from the process.