Shredder Feeding and Growth Rates

Low-order streams running through forests receive large amounts of tree leaves, which provide food for invertebrate shredders. Information on shredder ingestion of leaves and growth rates can be important in studies aiming to elucidate the ecology of shredders and how global change or stressful conditions such as exposure to pesticides may affect shredders. The aim of the procedures described in this chapter is to estimate feeding and growth rates of shredders. Specimens are individually allocated to chambers with known amounts of leaves offered as food. Ingestion is calculated as the decrease in leaf litter mass exposed to shredders for a defined period, assuming that the difference is due to feeding. Growth rates are measured as mass increase per unit of consumer body mass over time by assuming either linear or exponential growth. Typical ingestion rates range from 0.002 to 2.3 mg leaf dry mass mg−1 animal dry mass day−1 and growth rates range from ~0.2 to 16 μg mg−1 day−1. Application of the method has helped to identify opposing feeding strategies when exposed to food of contrasting quality: maximization of food intake and growth on high-quality litter or increased ingestion rates when feeding on a low-quality diet allowing constant growth.