Light Limitation in a Stream Ecosystem: Responses by Primary Producers and Consumers

作者：Walter R. Hill, Michael G. Ryon, Elizabeth M. Schilling · 发表于：Ecology · 年份：1995 · DOI：10.2307/1940936 · 被引用次数：427 · 研究领域：Fish Ecology and Management Studies、Freshwater macroinvertebrate diversity and ecology、Soil and Water Nutrient Dynamics

Heavy shade presents serious challenges for primary producers and food—limited herbivores in forest streams. In this study, we examined the response of periphyton and grazing snails (Elimia clavaeformis) to summer shade in White Oak Creek (WOC), a second—order stream in a Tennessee deciduous forest. Three experiments were performed: (1) in situ manipulation of light and snail density to test the effects of light limitation and grazing; (2) construction of photosynthesis—irradiance (P—I) curves to test for shade adaptation by periphyton; and (3) measurements of snail growth vs. irradiance, to qualify the indirect relationship between grazers and an abiotic constraint on photosynthesis. In the first experiment, light and snail densities were manipulated in a 2 X 2 factorial design: two light treatments were created by removing streamside vegetation from four sites in WOC and by pairing each of these sites with an adjacent, shade site; two snail density treatments at each site were created by adding snails at normal (970 individuals/m 2 ) and low (50 individuals/m 2 ) density to the two sides of Plexiglas channels. Snails at normal densities cropped periphyton biomass to low levels regardless of light regime, but periphyton productivity was higher at the open sites where snails grew faster and accumulated more lipid. Snail growth and lipid accumulation were strongly affected by intraspecific competition in both light regimes. In the second experiment, photosynthesis—irradiance c...