Do Inhibitory Interactions Between Detritivores Influence Leaf Breakdown?

Recent research suggests that inhibitory interactions among detritivore taxa may influence the effect of either taxa on detrital processing. Larvae of the stonefly Tallaperla maria were found to inhibit leaf consumption by larvae of the cranefly Tipula abdominalis in a previous study. I conducted a field experiment to determine whether Tipula consumption declined linearly with increasing Tallaperla density or if there was a threshold density of Tallaperla above which Tipula would cease to consume leaves. In 2013, I added 1 Tipula larva to enclosures containing conditioned yellow birch leaves along with increasing numbers of Tallaperla larvae. Enclosures with no insect larvae served as controls in which only leaching and microbial breakdown occurred. The presence of Tipula did not increase decomposition rates relative to microbial controls. Treatments of Tallaperla in enclosures at 2, 4, and 5 densities resulted in a significant increase in leaf breakdown relative to controls. No differences were found among treatments containing insect larvae. In 2014, I added 1 Tipula larva to enclosures containing increasing numbers of Tallaperla. Neither the presence of Tipula nor the addition of Tallaperla increased leaf breakdown rates relative to controls. In both years, leaf decomposition function was negatively correlated with increasing detritivore diversity.