Food Limitation of Two Lotic Grazers: Quantity, Quality, and Size-Specificity

Abstract

A food augmentation experiment demonstrated that growth and lipid accumulation by grazing snails (Elimia clavaeformis) and caddisflies (Neophylax etnieri) from a snail-dominated stream in eastern Tennessee were strongly food limited. Elimia (two size classes) and third-instar Neophylax from White Oak Creek were given one of four diets in laboratory streams: (1) low-biomass periphyton (from White Oak Creek), (2) high-biomass periphyton (from an unshaded, nutrient-enriched stream that lacked effective grazers), (3) low-biomass periphyton and leaves, and (4) high-biomass periphyton and leaves. Small Elimia grew 2× faster and large Elimia grew 5× faster on high-biomass periphyton than on their normal diet of low-biomass periphyton. Neophylax grew 7× faster on the high-biomass periphyton. The high-biomass periphyton also produced significantly higher ratios of lipid to ash-free dry mass for both grazers. Leaf additions did not increase growth or lipid accumulation, even for Elimia, a feeding generalist. Measur...