INSECT OUTBREAKS, RESOURCE PULSES, AND ECOSYSTEM RESILIENCE TO PERTURBATION: Hakalau Forest Reserve, HI
Resource pulses are short duration events of high resource availability, such as insect outbreaks or mast seed events, and are found across many different types of ecosystems. Pulse events are of ecological interest because they allow us to study factors that affect ecosystem resilience to perturbation. Concurrently, ecosystems are undergoing shifts in species composition due to habitat conversion and exotic species that may alter their resilience to perturbations. Various hypotheses suggest that invaders may be highly adept at taking advantage of high resources, because they have already proven their ability to adapt to novel systems, although these have not been explicitly tested in a resource pulse context. On the other hand, monocultures of one species or functional group, may not be as well equipped to take up resource pulses. Hawaiʻi Island is experiencing a massive defoliation event of its dominant hardwood, Acacia koa by a foliar-feeding caterpillar, Scotorythra paludicola. A diverse group of researchers from the USGS, University of Hawaiʻi, and USDA-Forest Service are monitoring Scotorythra moths and caterpillars, soil and plant nitrogen (N), tree mortality, predatory insects, and birds. Preliminary data from my work shows that large quantities of caterpillar frass have led to soil N pulses, increasing soil available N in some sites three-fold. Results suggest that sites with a more native, diverse understory show little sign of the soil N pulse. This could be due to higher biomass and productivity, or a greater niche breath than sites that have exotic grasses dominating the understory vegetation. Although these data are very preliminary, they point to interesting future research paths concerning species diversity and community response to perturbation.