Preface: Structure and Dynamics of Stream Fish Assemblages
Gary D. Grossman and John L. Sabo
In the 25 years since the symposium on ecology and evolution of stream fishes coordinated by Matthews and Heins (1987), we have made substantial progress in identifying the processes affecting the structure of, and interactions within, stream fish assemblages. For example, the majority of stream fish ecologists now accept that environmental variation in the form of both long- and short-term flow variation strongly affects many stream fish assemblages. These effects range from low levels of flow variation that provide a stable environment in which interspecific interactions may be important, to flashy streams in which assemblage structure varies from year to year. The importance of environmental variability to the dynamics of stream fish assemblages was hotly debated at the time of the first symposium, with many researchers espousing a strongly “competitionist” (McIntosh 1985) view of the world, that diversity and coexistence within stream fish assemblages only was maintained via partitioning of limited spatial or trophic resources. This debate now appears to be resolved and many stream fish ecologists view the maintenance or restoration of natural variability in flow as essential to the continuation or re-establishment of natural and diverse stream fish assemblages (Poff et al. 1997, 2007; Taylor 2010, this volume). That is not to say that resource limitation and predation are unimportant processes in stream fish assemblages (Harvey and Stewart 1991; Power et al. 2008), but it is to say that these processes cannot be invoked as the only mechanisms capable of explaining patterns in assemblage structure or resource use.