What is the right scale? Encouraging fruitful engagement for ecology with ecohydraulics

Abstract In ecohydraulics research, both physical and biological variables must be sampled at scales that are appropriate to the questions being addressed. This essay focuses on ecological topics that may be addressed in the context of ecohydraulics and the scales appropriate for their investigation. The first sections discuss definitions of scale, how environmental heterogeneity influences experimental and sampling designs, and the importance of recognizing that physical and ecological heterogeneity are not necessarily related. Thus, the scales appropriate for a particular research problem should be determined primarily by the ecological phenomenon of interest, plus the generation time and life-space of the study organisms. Studies over the large scales relevant to population and community ecology are logistically difficult and numerical models, but not scaled physical models, may facilitate extrapolations between scales for ecological phenomena. Three examples illustrate how complementary sets of studies executed at different scales can collectively contribute to ecological research problems in an ecohydraulics context. Two examples have strong roots in ecology (population dynamics in disturbed environments; ecosystem engineers) and the third arises from a need to solve applied problems (fish passage). These are topical areas of research to which ecohydraulics could make significant contributions.