Effects of Drought on Stream Insects and its Ecological Consequences

Global climate change scenarios predict more frequent and extended droughts, especially in the mid-latitudes. For many stream insects, these increasing periods of drought are likely to cause local if not regional extinctions, with potentially severe consequences for stream ecosystem function. Drought is a steadily intensifying 'ramp' disturbance that disrupts lateral, longitudinal and even vertical hydrological connectivity, depending on the spatial patterns of drying and drought severity. These hydrological changes affect many stream insects via impacts on refuges and water quality interacting with changes wrought by human activities. Selective extirpation of specific groups of insects during drought may alter benthic food web linkages or fundamental ecosystem processes such as organic matter breakdown. Management of flowing waters must consider these impacts, seeking to protect natural resilience (e.g. refuges) and explicitly acknowledging how drought affects aquatic insect community composition and function. However, there is much still to learn about drought and its impacts on stream insects. For example, we lack data from long-term studies that illustrate lag effects or other repercussions of droughts. Factors affecting rates and trajectories of post-drought recovery by stream insect communities are also poorly understood, hampering assessments of resistance and resilience to this increasingly common disturbance.