DOES WESTERN SPRUCE BUDWORM HERBIVORY ALTER MACROINVERTEBRATE COMMUNITY COMPOSITION AND STREAM FOOD-WEB DYNAMICS?
In the Pacific Northwest, herbivorous Western Spruce Budworm (WSB) outbreaks have increased intensity and extent along Douglas-fir forest riparian areas. As headwaters rely on riparian energy and nutrient subsidies, WSB outbreaks could increase headwater stream resources. We hypothesized that frass inputs from WSB herbivory would directly elevate stream resources and solar radiation via canopy defoliation. We predicted higher diversity in headwater streams with high herbivory from more heterogeneous food resources. We also predicted greater total macroinvertebrate density and more collectors from increased energy and nutrient inputs in headwaters exposed to high WSB herbivory. Macroinvertebrate communities were compared between headwater streams with low (n=4) and high (n=4) WSB herbivory. We found total density was greater in high WSB herbivory sites, but contrary to our prediction, diversity was greater in the low WSB herbivory sites. Increased shredder and scraper densities in high WSB herbivory sites may be from added frass as a food resource. Additional stable isotopic analysis of food resources are needed to determine contribution of frass to macroinvertebrates. Our results will quantify the effects of herbivorous WSB outbreaks on community composition and stream food-web interactions.
Deion Everhart (Primary Presenter/Author), University of Central Arkansas, firstname.lastname@example.org;