MACROINVERTEBRATE COMMUNITIES, SECONDARY PRODUCTION, AND LIFE-HISTORYPATTERNS IN 2 ADJACENT STREAMS IN IDAHO, USA

We compared community attributes, secondary production, and life histo ries of macroinvertebrates in two adjacent streams with contrasting en vironmental characteristics. Environmental variables (measured as coef ficients of variation) were up to an order of magnitude greater in Lit tle Lost River (Lost River) than in Birch Creek. Ln particular, the fl ow regime was 12 x more variable in Lost River, a stream fed largely b y surface runoff, than in Birch Creek, a groundwater-fed stream. Birch Creek accumulated more annual degree days, had higher ionic concentra tions, and developed greater periphyton biomass than Lost River. Altho ugh? the mean density of macroinvertebrates was similar between the st reams, species richness was higher and mean biomass was lower in Lost River. Annual macroinvertebrate production was dominated by Chironomid ae and was 1.6 x higher in Lost River than :Birch Creek. However, if C hironomidae are excluded, total annual production was 1.5 x greater in Birch Creek than in Lost River. Life cycles of some common taxa refle cted the different environmental conditions in each stream. Our data s upport the idea that certain attributes of macroinvertebrate assemblag es (density, biomass, and production) are structured by environmental factors regulating growth (e.g. water chemistry, thermal loading, peri phyton), whereas other biotic attributes (e.g. species richness, assem blage composition, and life histories) are more influenced by thermal and flow regimes.