Individual-based model of yellow perch and walleye populations in Oneida Lake

Predator-prey dynamics and density dependence are fundamental issues in eco logy. We use a detailed, individual-based model of walleye and yellow perch to investigate the effects of alternative prey and compensatory responses on predator and prey population dynamics. Our analyses focus on the numeric al and developmental responses of the predator, rather than the traditional emphasis on functional responses. The extensive database for Oneida Lake, New York, USA was used to configure the model and ensure its realism. The m odel follows the daily growth, mortality, and spawning of individuals of ea ch species through their lifetime. Three ecologically distinct periods in t he history of Oneida Lake were simulated: baseline, high mayfly densities, and high forage fish densities. Mayflies and forage fish act as alternative prey for walleye. For model corroboration, the three periods were simulate d sequentially as they occurred in Oneida Lake. Model predictions of abunda nces, size at age, and growth and survival rates compared favorably with On eida Lake data. Three hypotheses suggested by the data were evaluated: alte rnative prey stabilizes yellow perch and walleye populations; alternative p rey increases yellow perch and walleye recruitment; and density-dependent g rowth and survival compensate for changes in young-of-the-year mortality. M odel simulations were performed under increased mayfly densities, increased forage fish densities, and increased egg mortality rates. Predicted recrui tment and population stability depended on the magnitude of increased walle ye prey and differed between mayflies and forage fish. Compensation was dri ven by density-dependent growth, resulting in younger age at maturation and increased fecundity. We compare our results using a detailed, size-structu red model capable of numerical and developmental responses of predators to results from classical predator-prey theory. Weaknesses in the current vers ion of the individual-based model and knowledge gaps that require additiona l empirical data collection are also discussed.