Resource Pulses and Spatial Subsidies in Ozark Karst Springs: Effects on Community Structure and Food Webs

Abstract

Spatial and temporal patterns of invertebrate community composition, biomass, functional diversity, foodweb dynamics, and foodweb complexity were examined in three Ozarks springs. Also examined was the effect of an experimental manipulation of algal production (function of light limitation) on foodweb pathways and complexity. Food source-consumer interactions were determined using carbon and nitrogen stable isotope and stoichiometric analyses. Biocomplexity and functional diversity increased temporally and spatially along the spring source-springbrook gradient likely due to variability in the composition and availability of food sources. Foodweb analyses indicated that the trophic base of the foodweb was autochthonous, shifting temporally towards a greater reliance on allochthonous resources. Spatial and temporal shifts in food availability and utilization were associated with corresponding increases in foodweb complexity. Isotope ratios, based on manipulation of algal production, indicated a shift toward more allochthonous-based pathways and increases in omnivory and foodweb complexity in manipulated (shaded) sections of the spring.