Doctoral Dissertations

Date of Award

8-1998

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Ecology and Evolutionary Biology

Major Professor

James Drake

Committee Members

Kenneth Rose, Tom Hallam, Dewey Bunting

Abstract

A general individual-based fish community simulator is presented. The model tracks the daily feeding, growth, movement, reproduction, and mortality of individuals of up to six species for multiple generations in up to three spatial boxes. The version presented in this dissertation is based on Lake Mendota, Wisconsin. Six species are followed: yellow perch, bluegill, white bass. cisco, walleye, and northern pike. The environment consists of daily temperature, dissolved oxygen, and prey densities in each of the epilimnion, hypolimnion, and littoral zone spatial boxes. Feeding parameters and larval mortality rates were calibrated until all species persisted at reasonable biomasses, with realistic mean lengths at age and diets by life stage. A general introduction and overview is given in Part 1. In Part 2 alternative baseline calibrations are presented which differ in their degree of interannual variability. Correlation analysis of survival and growth rates showed that larvae were influenced by competition, yearlings by predation, and young of the year (YOY) juveniles by both. Adult growth was density-dependent for planktivores and positively related to forage biomass for piscivores. Cisco dynamics were effectively independent of the other species. The calibrated model was used to compare the effects of a biomanipulation experiment (piscivore enhancement) versus a coincident cisco die-off event, and to evaluate alternative stocking regimes for their ability to sustain improved water quality. Predicted total zooplankton consumption was used to indicate effects on algae and water quality. The effects on community composition of piscivore enhancement and cisco die-off differed between the low and high variability baseline conditions. Under both baseline conditions, cisco die-off produced similar short-term but much larger long-term reductions in zooplankton consumption than piscivore enhancement. Delayed changes in YOY juvenile and larval survival illustrated complex indirect food web responses to piscivore enhancement. None of the three alternative stocking regimes analyzed yielded ideal management results. Stocking either had little effect on zooplankton consumption or resulted in significant changes in piscivore mean lengths or in the composition of the fish community. In Part 3 the importance of food web structure in determining population responses to global climate change is examined. Six alternative food webs were configured as subsets of the 6-species Lake Mendota food web: two versions of the 6-species food web, which differed in yellow perch biomass, a 3-species (yellow perch, bluegill, white bass) competition food web, two versions of a 2-species (yellow perch, walleye) predator-prey food web differing in yellow perch biomass, and a 1-species (yellow perch) population model. All food webs included yellow perch. To simulate climate change, published predictions of changes in temperature and dissolved oxygen in Wisconsin lakes under 2x atmospheric COj were superimposed onto temperature and dissolved oxygen profiles for Lake Mendota. Population responses of yellow perch to climate change depended upon food web arrangement. Yellow perch abundance decreased in response to climate change in the 3-species and high-biomass 6-species food webs, and increased in the remaining food webs. Population responses in the 1 -species model were consistent with predictions based only on yellow perch bioenergetics (increases in size, abundance, and biomass), but were modified in other food web by competition and predation in the model. White bass and northern pike were relatively minor components of the food web under baseline conditions but emerged as dominant species under climate change. A summary of results and concluding remarks are given in Part 4. Adapting to environmental changes will require understanding of changing ecological processes at many levels. Individual-based models provide a method for integrating processes from individuals to communities.

Key words: individual based, multi-species, fish, simulation model, biomanipulation. Lake Mendota, predation, density dependence, depensatory mortality, population dynamics, food web global warming, climate change.

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