The influence of environmental heterogeneity on patterns and processes in streams

This introduction to 9 articles on the influence of heterogeneity on pattern and processes in streams describes why we need to examine heterogeneity and outlines major themes we need to consider. Contributors show that a wide range of lotic patterns and processes may be influenced by physical and biological heterogeneity, including the spatial distribution and persistence of biota, predator-prey interactions, and flux of materials among ecosystem compartments. Authors have relied on both theoretical approaches (e.g., numerical simulation models) and empirical approaches (e.g., manipulative experiments) to garner insights into the causes and consequences of spatial and temporal variability in streams. We outline 6 major themes that emerged from this collection of papers and from the symposium on ecological heterogeneity held at the 1995 meeting of the North American Benthological Society in Keystone, Colorado. These themes encompass much of the nature of heterogeneity, and they have important implications for the study of pattern and process in streams. To elucidate on these themes, we provide specific examples from the papers in this series.