Preface: When and Where Do Fish Have Strong Effects on Stream Ecosystem Processes?
Michael J. Vanni
The notion that fishes, or for that matter animals in general, can have strong effects on stream ecosystems is a relatively new idea. This is evident when comparing the composition of this volume with that of the Matthews and Heins (1987) book. The latter contains only two chapters explicitly focused on how fish affect other biota, and the effects of fish on bona fide “ecosystem processes” (e.g., primary production, nutrient cycling) were discussed in only one of these chapters (Matthews et al. 1987). In contrast, this volume has an entire section, consisting of four chapters, focused on the importance of fishes in stream ecosystems.
The evolution of the idea that fish can be important at the ecosystem scale is also mirrored in trends in general stream ecology books over the past several decades. The Hynes (1970) classic text on stream ecology contains no mention of the idea that fishes can mediate stream ecosystem processes; interspecific competition is the only biotic interaction involving fish that is discussed. More generally, there is essentially no discussion of community- or ecosystem-level impacts of predation by fish or other animals. There is also very little discussion of nutrient cycling, whether by fish or other animals, or of biotic regulation of nutrients in general. In essence, the prevailing idea was that the influence of physical factors, namely flow regime, overwhelmed biotic interactions in structuring communities and regulating ecosystem processes. In contrast, Allan and Castillo’s (2007) book on stream ecology has two entire chapters dedicated to species interactions and communities (plus a chapter on energy flow through food webs), and these include sections on community-level effects of grazers and predators, trophic cascades, and food web interactions. Additionally, Allan and Castillo’s (2007) chapter on nutrient dynamics includes a significant section on consumer (animal) effects on nutrient dynamics.