Long-term variability, disturbance, and biological traits of aquatic invertebrates in Mediterranean-climate streams

Disturbance in mediterranean-climate streams can result from natural (e.g., flooding and drying) or human-induced (e.g., fire) processes. I examined long-term temporal variability of benthic macroinvertebrate communities and their biological traits in response to periods of floods and droughts, and to the impacts of a prescribed fire on aquatic and riparian communities in a Sierra Nevada mixed-conifer forest.; I assessed temporal change and response to disturbance using univariate and multivariate analyses, based on three long-term datasets from northern California streams: 17--20 years at four sites in Hunting and Knoxville Creek (Lake Co.); 7 years at Big Sulphur Creek (Sonoma Co.); and 7--8 years at six sites in Blodgett Forest Research Station (El Dorado Co.). Biological traits were coded for 263 macroinvertebrate taxa. The life history of the caddisfly Heteroplectron californicum was examined using monthly data (1.5 years) from Webb Creek (Marin Co.).; Biological-trait composition is relatively more stable than community composition and abundance both between seasons and among years. However, seasonal and annual changes in habitat from variable precipitation patterns are reflected in biological-trait composition. Traits conferring resilience or resistance to flooding or drying are more common in both wet seasons and years, and dry seasons and years, respectively. Extreme multi-year droughts resulted in long lasting, directional change in communities. Some taxa are temporally rare; up to one-third of taxa at a site only occurred once in 7--20 years. Prescribed fire was patchy in the riparian zone and had short-term or no effects on water chemistry, sediment, large woody debris, periphyton, and benthic macroinvertebrate communities. The life history of a wood-boring caddisfly, Heteroplectron californicum, was found to be one-year with some cohort-splitting.; In mediterranean-climate streams several patterns are evident: (1) long-term variability (both seasonal and annual) of aquatic macroinvertebrate communities results from interannual variability in precipitation, (2) the effects of droughts are long-lasting, (3) temporal rarity of invertebrate taxa is common in long-term datasets, (4) there are minor and short-term effects of a small-scale prescribed fire on stream and riparian communities, and (5) biological traits provide mechanistic understanding of community-level variation and relationships in response to habitat conditions.