Macroinvertebrate communities, secondary production, and life history patterns in two adjacent streams in Idaho, USA

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We compared community attributes, secondary production, and life histories of macroinvertebrates in two adjacent streams with contrasting environmental characteristics. Environmental variables (measured as coefficients of variation) were up to an order of magnitude greater in Little Lost River (Lost River) than in Birch Creek. In particular, the flow regime was 12 x more variable in Lost River, a stream fed largely by surface runoff, than in Birch Creek, a groundwater-fed stream. Birch Creek accumulated more annual degree days, had higher ionic concentrations, and developed greater periphyton biomass than Lost River. Although, the mean density of macroinvertebrates was similar between the streams, species richness was higher and mean biomass was lower in Lost River. Annual macroinvertebrate production was dominated by Chironomidae and was 1.6 x higher in Lost River than Birch Creek. However, if Chironomidae are excluded, total annual production was 1.5 x greater in Birch Creek than in Lost River. Life cycles of some common taxa reflected the different environmental conditions in each stream. Our data support the idea that certain attributes of macroinvertebrate assemblages (density, biomass, and production) are structured by environmental factors regulating growth (e.g. water chemistry, thermal loading, periphyton), whereas other biotic attributes (e.g. species richness, assemblage composition, and life histories) are more influenced by thermal and flow regimes.