Climate Change Impacts on Community Resilience. Evidence from a Drought Disturbance Experiment

Climate change is expected to alter disturbance regimes with profound effects on the structure and dynamics of ecological communities. In many regions, climate models forecast shifts in precipitation patterns that will exacerbate droughts in rivers and streams, yet ecological impacts on freshwater ecosystems remain poorly understood. We report the results of a stream mesocosm experiment designed to test the effect of drought on the resilience of replicate macroinvertebrate communities, via direct manipulation of flows. Drying disturbances applied at high (monthly) and low (quarterly) frequency over 21-months had contrasting effects on the structure and temporal dynamics of the communities. Macroinvertebrates were resilient to low-frequency disturbance, sustaining abundant and diverse communities, which developed over experimental time. By comparison, high-frequency disturbance exceeded the capacity for recovery, skewing community structure, and generated relatively impoverished, static assemblages dominated by fewer species. Species responses ranged from extirpation to irruption, with smaller short-lived taxa (≤. 1 generation per year), notably chironomids and worms, replacing larger taxa with longer life cycles (≥. 1 generation per year). This research provides one of the first experimental tests of resilience to drought in aquatic ecosystems.