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Presented at the NABS Annual meeting, Athens, Georgia, 2003
in Community Ecology II
A stream field experiment on the effects of light levels across a nutrient gradient on algae and invertebrate grazers
W.K. Taulbee. Department of Biology, University of California, Santa Barbara, California 93106
Light and inorganic nutrients are often the most important resources for primary producers, but primary producers can respond differentially to changes in the relative and absolute levels of each of these resources, which can subsequently affect the behavior of primary consumers. The combined effects of stream shading and nutrient level on benthic algae and invertebrate grazers were examined in 24 in situ stream channels in the eastern Sierra Nevada of California. Two light levels and six nutrient levels were cross classified, with two replicates per treatment, and the effects of these manipulations on algal biomass and quality were followed over three weeks. After three weeks, 100 Baetis mayflies were added to half of these channels, and Baetis epibenthic densities and emigration rates were determined over the next three days. In general, light and nutrient levels had significant independent and interactive effects for algal biomass and elemental composition. The indirect effects on Baetis mayflies were less pronounced, but the interaction between light and nutrients was a marginally significant predictor for per capita emigration. These results suggest that stream communities respond differentially to resource enrichment, depending on the absolute and relative levels of light and nutrients.
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