Environmental heterogeneity and its effect on species richness and abundance is currently a focal point of research in ecology, and nowhere is spatial-temporal variation greater than in rivers and streams. The communities of invertebrates, that have evolved in concert with the unique patterns of physico-chemical variability typical of these habitats, exhibit a range of traits that is most useful in testing modern ecological paradigms. The overall, longterm objective of our lab's research programme is to understand the ecological processes that control the distribution, formation, structure and dynamics of running water communities. Because control is believed to act hierarchically, we carry out research at the levels of community, population and individual. Emphasis is currently directed towards studies of freshwater springs, estuaries, tropical rivers, temporary streams, and the hyporheic zone.