9701332 Lewis While biodiversity continues to be the focus of many ecological studies and conservation efforts, its relation to ecosystem function remains unresolved. The literature provides examples of both interdependence and independence between biodiversity and functioning of ecosystems. The purpose of this project is to test three hypotheses, as follows: (1) a given biotic compartment in an incrementally stressed ecosystem will show suppression of biodiversity first, and suppression of biomass subsequently; (2) suppression of ecosystem function is primarily related to suppression of biomass, rather than to biodiversity per se; and (3) suppression of biomass differs among biotic compartments according to a predictable series of thresholds: multicellular organisms < unicellular autotrophs < microbial decomposers. These hypotheses will be tested on a group of streams, some of which have been stressed by acidic mine drainage. These streams are excellent model systems because they include a wide gradient of multiple stresses (low pH, high concentration of metals, oxide deposition), each of which is quantifiable. Pilot studies on these streams are consistent with the three hypotheses. The project will focus on expansion of the information on benthic insects and periphyton as necessary to test the hypotheses, and use of molecular techniques to obtain comparable information on microbial decomposer compartments.
