This project will describe the spatial and temporal patterns of trophic structure and the proportion of total biomass in primary producer, primary consumer, and secondary consumer trophic levels in a desert stream ecosystem. The spatial context for this description will be a hierarchical arrangement of patches from the relatively small scale of algal or macrophyte assemblages to large scale run-riffle-pool habitats. Temporal change will be assessed along successional trajectories associated with flooding and drying. Losses and gains of biomass at each trophic level will be evaluated both within and between patches to determine how patches are linked. Experiments will identify mechanisms shaping trophic structure and causing observed temporal changes in trophic structure. Mesocosm experiments will manipulate resources and consumers in 3-level systems, and a natural stream experiment will manipulate nutrients and top predators. Descriptive and experimental results will be used to evaluate ecosystem-level consequences of specific trophic configurations; this evaluation will indicate whether change in community-level properties drives change in ecosystem structure and function. This research explores questions concerned with the relative influence of top-down (propagated from the top to the bottom of the food chain) and bottom-up (propagated from the base) processes in determining patterns observed in nature. These are important issues concerned with the responses of ecological systems to disturbance. The facilities for this research are excellent; the investigators are productive and innovative experts in the area of stream ecology.
