Flow conditions, benthic food resources, and invertebrate community composition in a low-gradient stream in Missouri

We examined how community measures (richness, diversity, density), community composition las measured by ordination site scores), and functional-feeding-group composition of benthic invertebrates were related to stream hydraulics and benthic food resources within the Jacks Fork River in Missouri, USA. Invertebrates were collected in the autumn of 1992 and spring of 1993 from 11 habitats in upper, middle, and lower stream segments encompassing a full range of physical and hydraulic conditions. Community composition, diversity, and relative densities of some of the functional groups were highly correlated with hydraulic variables such as current velocity, Froude number, and Reynolds number and with some measures of benthic organic matter. Ordination also revealed a gradual, longitudinal change in invertebrate community composition that was not related to simple or complex hydraulic variables. Taxa richness, density, and diversity were generally not correlated to this gradient. Overall, variation in community composition within any 1 segment of stream was greater than variation throughout the total stream system, indicating that local factors had the greatest influence on the invertebrate community Composition was the community property and current velocity was the environmental variable most likely to be correctly extrapolated over space and time within this relatively pristine stream system.