The influence of a neotropical herbivore (Lamponius portoricensis) on nutrient cycling and soil processes.

The role of phytophagous insects in ecosystem nutrient cycling remains poorly understood. By altering the flow of litterfall nutrients from the canopy to the forest floor, herbivores may influence key ecosystem processes. We manipulated levels of herbivory in a lower montane tropical rainforest of Puerto Rico using the common herbivore, Lamponius portoricensis (Phasmatidea), on a prevalent understory plant, Piper glabrescens (Piperaceae), and measured the effects on nutrient input to the forest floor and on rates of litter decomposition. Four treatment levels of herbivory generated a full range of leaf area removal, from plants experiencing no herbivory to plants that were completely defoliated (>4,000 cm(2) leaf area removed during the 76-day study duration). A significant (P<0.05) positive regression was found between all measures of herbivory (total leaf area removed, greenfall production, and frass-related inputs) and the concentration of NO (3) (-) in ion exchange resin bags located in the litter layer. No significant relationship was found between any of the herbivory components and resin bag concentrations of NH (4) (+) or PO (4) (-) . Rates of litter decay were significantly affected by frass-related herbivore inputs. A marginally significant negative relationship was also found between the litter mass remaining at 47 days and total leaf area removed. This study demonstrated a modest, but direct relationship between herbivory and both litter decomposition and NO (3) (-) transfer to the forest floor. These results suggest that insect herbivores can influence forest floor nutrient dynamics and thus merit further consideration in discussions on ecosystem nutrient dynamics.