What Do Species Do in Ecosystems?

Three aspects of the role of species in ecosystems are reviewed. (1) Theoretically, what are the possible relationships between ecosystem processes (Likens' (1992) transformation and flux of energy and matter) and the species richness of communities ? (2) Summaries of two experiments with artificially constructed terrestrial ecosystems in the controlled environment facility known as the Ecotron are described. The first draws attention to the role of earthworms as ecosystem engineers; the second explores changes in ecosystem processes in mesocosms assembled with three different levels of biological diversity