Resistance of aquatic insects to a low-flow disturbance: exploring a trait-based approach

Abstract Low-flow disturbances are predicted to increase in frequency and intensity because of climate change and extensive human water withdrawal, but the effect of decreased flow on aquatic insect communities is not well understood. I explored the resistance of aquatic insects to reduced flow by creating an experimental low-flow disturbance that diverted ∼40 to 80% of the water in 3 replicate streams for 2 summers. I sampled the aquatic insect community in control and treatment reaches before and during the 3-mo water diversions. I used a trait-based approach to analyze the data because traits have the potential to increase mechanistic understanding and predictive capabilities. The analysis focused on 6 traits: desiccation resistance, maximum crawling rate, armoring, size at maturity, rheophily, and habit. Community trait composition underwent strong seasonal shifts, but few consistent responses to reduced flow were observed. The 2 trait states that did appear to confer increased resistance were high crawling rate and armoring. These trait states can provide protection from predators. Thus, biotic interactions might be important during low-flow disturbance.