Foundations of stream ecology

Ecologists engaged in the study of running waters have developed a number of conceptual models whose purpose is to synthesize empirical information that describes structure, function, and processes of lotic ecosystems over their enormous range of natural variations. Such models are of great value in organizing what might otherwise be a collection of seemingly unique case studies into a broader understanding based on unifying principles. They gain power and acceptance from their ability to predict outcomes in new settings and explain differences observed among, for example, streams of differing discharge or occurring in different landscape and climatic settings. Models occasionally are proven inadequate, but exceptions also can strengthen models by revealing needed extensions.

Students wishing to explore the full range of models that currently influence our thinking about streams and rivers will benefit from the papers by Minshall et al. (1983), Statzner and Higler (1985), Junk et al. (1989), Petts (1984) Townsend et al. (1994), Poff et al. (1997), Lorenz et al. 1997, Lake (2000), Galat and Zweimuller (2001), Poole (2002), Ward et al. (2002), Weins

(2002), Benda et al. (2004), and Thorp et al. (2006). Two models in particular, the river continuum concept (Vannote et al. 1980) and nutrient spiraling (Newbold et al. 1982a), have been especially influential to this generation of stream ecologists. More recently, the long-standing recognition that fluvial networks are both heterogeneous and hierarchical has been freshly infused by collaborations between ecologists and geo-morphologists, leading to more explicit formulations of the episodic connectivity of spatially distinct units, and hence more appreciation of discontinuities along the continuum (Poole 2002, Ward et al. 2002, Thorp et al. 2006). An expanded view of scale, both temporal and spatial, enhanced through the contributions of hydrologic and geomorphological studies and with concepts from landscape ecology (Weins 2002), has greatly benefited stream ecology. At smaller scales extending down to cellular and molecular processes, new methods using isotopes and tools of microbial ecology promise rapid advances in our understanding of underlying mechanisms (Zak et al. 2006). Perhaps inadequately captured at present in the conceptual models discussed by the authors cited above, advances in our ability to understand functional relationships at the microbial and molecular scales may drive many of the advances in lotic ecology in coming decades.

Today's students have the enviable opportunity to observe future developments in stream ecology, and we have little doubt that the next several decades will be as exciting as recent decades. In closing, we provide our short list of foundational principles on which the future will build. Students can gain a diversity of viewpoints by consulting the papers cited within.

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