Effects of manipulation of basal resources on food web pathways in karst spring ecosystems

 Effects of Manipulation of Basal Resources on
Food Web Pathways in Karst Spring Ecosystems
Teresa M. Carroll¹ and James H. Thorp²

¹Department of Biology, Drury University, Springfield, MO 65802; tcarroll@drury.edu; 417-873-6971; FAX 417-873-7278

²Kansas Biological Survey and Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS 66047; thorp@ku.edu; 785-864-1532; FAX 785-864-1537

 Studies of ecosystem function and trophic dynamics of surface systems are often poorly understood, limited in space and time, and focused on a single consumer trophic level rather than involving manipulation of basal resources. In contrast, we experimentally manipulated microalgae in an Ozark springbrook food web that issues from a small cave, is fueled by hypogean allochthonous materials, and is therefore considered a heterotrophic system. While most cave-based springs resemble heavily forested streams, this spring's riparian zone has been partially deforested, and autochthonous production should be the dominant basal resource. To evaluate the relative importance of autochthonous production to the trophic food web, we experimentally reduced the production of benthic algae to invertebrate communities enclosed in cages, half of which were placed under a canopy of polyethylene shade cloth (techniques mimicking the percentage of shading in 2 similar Ozarks springs; % light penetration = ~ 20% PAR). Clay tiles were secured in each treatment area to determine the relative availability of benthic algae to consumers (as Chl-a). Consumer isotope ratios indicated a shift toward more allochthonous-based food web pathways and an increase in importance of feeding generalist in manipulated sections compared to that in the spring's control sections.