Transactions of the American Fisheries Society 122:459-466. 1993 Linking Life History Theory, Environmental Setting, and Individual-Based Modeling to Compare Responses of Different Fish Species to Environmental Change WEBSTER VAN WINKLE, KENNETH A. ROSE, KIRK O. WINEMILLER, DONALD L. DEANGELIS, AND SIGURD W. CHRISTENSEN Environmental Sciences Division. Oak Ridge National Laboratory Post Office Box 2008. MS-6038. Oak Ridge. Tennessee 37831-6038. USA ROBERT G. OTTO R. G. Otto & Associates. Post Office Box 306. Vienna. Maryland 21869. USA BRIAN J. SHUTER Fisheries Research Section. Ontario Ministry of Natural Resources Box 5000. Maple. Ontario L6A JS9. Canada Abstract.-We link life history theory, environmental setting, and individual-based modeling to compare the responses of two fish species to environmental change. Life history theory provides the framework for selecting representative species, and in combination with information on im- portant environmental characteristics, it provides the framework for predicting the results of model simulations. Individual-based modeling offers a promising tool for integrating and extrapolating our mechanistic understanding of reproduction, growth, and mortality at the individual level to population-level responses such as size-frequency distributions and indices of year-class strength. Based on the trade-offs between life history characteristics of striped bass Morone saxatilis and smallmouth bass Micropterus dolomieu and differences in their respective environments, we pre- dicted that young-of-year smallmouthbass are likely to demonstrate a greater compensatory change in growth and mortality than young-of-year striped bass in response to changes in density of early life stages and turnover rates of zooplankton prey. We tested this prediction with a simulation experiment. The pattern of model results was consistent with our expectations: by the end of the first growing season, compensatory changes in length and abundance of juveniles were more pro- nounced for smallmouth bass than for striped bass. The results also highlighted the dependence of model predictions on the interplay between density of larvae and juveniles and characteristics of their zooplankton prey. Predicting the responses of fish populations to In this paper we link life history theory, envi- environmental change continues to be a major ronmental setting (i.e., the spatial and temporal challenge in fisheries science. Populations are rou- characteristics of the abiotic and biotic compo- tinely challenged by natural and anthropogenic nents of the local environment), and individual- changes in the environment, such as variations in based modeling to compare the responses of two temperature and runoff and changes in stocking fish species to environmental change. Life history and fishing practices. In trying to interpret popu- theory provides the framework for selecting rep- lation responses to such changes, scientists are resentative species, and in combination with in- faced with a diversity of life history strategies, life formation on important environmental character- stages, and environmental settings (Winemiller and istics, it provides the framework for predicting the Rose 1992); limited understanding of mechanisms results of model simulations. Individual-based involved in regulation of populations and com- modeling offers a promising tool for integrating munities (Rothschid 1986); and evidence indicat- and extrapolating mechanistic understanding of ing that differences among individuals are likely reproduction, growth, and mortality at the indi- to be important (Lomnicki 1992). Given this sit- vidual level to population-level responses such as uation, we believe that integrating existing knowl- size-frequency distributions and indices of year- edge about the processes underlying reproduction, class strength. Based on the trade-offs between life growth, and mortality of individuals belonging to history characteristics of striped bass Morone sax- fish species with different life histories will help at His and smallmouth bass Micropterus dolomieu scientists meet the challenge of prediction. and differences in the environments of these two 459