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Energy Availability, Spatial Heterogeneity and Ecosystem Size Predict Food-Web Structure in Streams

R. M. Thompson and C. R. Townsend
Oikos
Vol. 108, No. 1 (Jan., 2005), pp. 137-148
Published by: Wiley on behalf of Nordic Society Oikos
Stable URL: http://www.jstor.org/stable/3548498
Page Count: 12
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Energy Availability, Spatial Heterogeneity and Ecosystem Size Predict Food-Web Structure in Streams
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Abstract

We used standardized techniques to assemble eighteen food webs in streams. Our aim was to identify the determinants of food-web structure with particular reference to energy availability (related to land use), spatial heterogeneity and ecosystem size (both independent of land use). Forested streams displayed lower algal productivity and higher standing crops of organic matter than the grassland streams. The organic matter in the pine streams was probably of lower quality than that elsewhere. Measures of energy availability and spatial heterogeneity predicted species richness and connectance. A combination of energy availability, spatial heterogeneity and ecosystem size accounted for the representation of particular invertebrate feeding groups in the streams. Algal production and organic matter standing crop were important determinants of invertebrate biomass and overall food-web structure. Grassland sites showed a positive relationship between algal productivity and food chain length whereas forest sites displayed a positive relationship between ecosystem size and food chain length. Therefore, these results provide support for both Pimm's productivity hypothesis and Cohen and Newman's ecosystem size hypothesis.

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