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<br />Hesse & Mestl 1993) exhibit one or more shortcomings. These shortcomings can include a <br /> <br />failure to consider the hydrologic needs of more than a few species or species groups; a failure <br /> <br />to consider the role of hydrologic processes in geomorphic changes or ecosystem functions, <br /> <br />such as material transport and cycling or food web support; or a failure to consider the full <br /> <br />range of temporal variability in hydrologic regimes (beyond simple characterizations suchas~ <br /> <br /> <br />mean monthly flows or flood frequencies). In addition, investigations of human perturbatio!Js <br /> <br /> <br />to hydrologic regimes have been far too limitedin,scope and detail, thereby.constraining.oUJt <br /> <br /> <br />perceptions of the linkages between hydrologic alteration and ecosystem degradation. . ,Y,;t] (,', <br /> <br /> <br />Clearly, it is impossible to know the hydrologic requirements of all species or therolc. <br /> <br /> <br />of all hydrologic processes in ecosystem structure andfurn;tion. In the absence of. ;is ,t:l1l2 <br /> <br /> <br />comprehensive knowledge about biohydrologic relationships within an ecosystem, ma~t <br /> <br /> <br />decisions generally have been based upon the known or perceived hydrologic requirements;of; <br /> <br /> <br />one, or at most a few, target species (Reiser et al. 1989). Generally, the targeted species;baVe <br /> <br /> <br />been limited to those occurring in aquatic environments; for instance, the vast majority of <br /> <br /> <br />instream flow prescriptions and water, rights. have been based upon the requirements off'OO; <br /> <br /> <br />alone (e.g., Bishop et al. 1990; Jirka & Homa 1990; Beecher 1990; Kulik 1990; Zincone&u": <br /> <br /> <br />Rulifson 1991). When environmental management decisions are based upon the hydrologiec;, .... <br /> <br /> <br />requirements of only a few aquatic species, the needs of other species, as well as ecosystenr)!h. <br /> <br /> <br />processes and functions, are neglected and may even be compromised by the resulting" . :hAqZ' <br /> <br /> <br />management prescription. Hill & Platts (1991) pointed out that when the hydrologic .f; 'me <br />requirements of both aquatic and riparian species and communities are considered, perceptions: <br />of the range of flows needed to sustain these systems may be expanded well beyond what '''" <br /> <br />3 <br />