All herbivores (both vertebrate and invertebrate) can directly
influence soil nutrient inputs through excrement (frass). Frass
inputs from canopy insect herbivores have been shown to influence
soil invertebrates and alter nitrogen and carbon cycles
(Reynolds et al., 2003a), and variation in soil nitrogen has been
shown to alter plant diversity (Wedin& Tilman, 1996, Fig. 3).