Abstract
Lotic fish have developed life history strategies adapted to the natural variation
in stream flow regimes. The natural timing, duration, and magnitude of flow events has
contributed to the diversity, production, and composition of fish assemblages over time.
Studies evaluating the role of hydrology in structuring fish assemblages have been more
common at the local or regional scale with very few studies conducted at the continental scale.
Furthermore, quantitative linkages between natural hydrologic patterns and fish assemblages
are rarely used to make predictions of ecological consequences of hydrologic alterations. We
ask two questions: (1) what is the relative role of hydrology in structuring fish assemblages at
large scales? and (2) can relationships between fish assemblages and natural hydrology be
utilized to predict fish assemblage responses to hydrologic disturbance? We developed models
to relate fish life histories and reproductive strategies to landscape and hydrologic variables
separately and then combined. Models were then used to predict the ecological consequences
of altered hydrology due to dam regulation. Although hydrology plays a considerable role in
structuring fish assemblages, the performance of models using only hydrologic variables was
lower than that of models constructed using landscape variables. Isolating the relative
importance of hydrology in structuring fish assemblages at the continental scale is difficult
since hydrology is interrelated to many landscape factors. By applying models to damregulated
hydrologic data, we observed some consistent predicted responses in fish life history
strategies and modes of reproduction. In agreement with existing literature, equilibrium
strategists are predicted to increase following dam regulation, whereas opportunistic and
periodic species are predicted to decrease. In addition, dam regulation favors the selection of
reproductive strategies with extended spawning seasons and preference for stable conditions.