Nutrient-specific foraging by Glossosoma intermedium larvae leads to conspecific case grazing

AbstractNutrient-specific foraging, or selection of resources based on nutritional quality, is a strategy homeostatic consumers use to meet their dietary nutritional needs. Glossosoma intermedium is a homeostatic caddisfly that often grazes nutrient-rich periphyton colonizing the cases of conspecific larvae. We hypothesized that case grazing may be the result of nutrient-specific foraging under conditions where streambed periphyton is nutrient deficient. To test this hypothesis, we monitored larvae in experimental streams. We measured case-grazing frequency and duration under 4 treatments of streambed periphyton: ambient (control), +N, +P, and +NP. Case-grazing frequency was significantly lower in the +NP treatment than in the other treatments, suggesting that nutritional quality influences resource selection by G. intermedium. However, duration of case-grazing bouts was not influenced by treatment. In addition, grazing by G. intermedium increased streambed periphyton C∶P and N∶P more in the +P treatment ...