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Browsing by Author "Jester, Douglas B. Jr."

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    A General Population Dynamics Theory for Largemouth Bass
    Jester, Douglas B. Jr.; Garling, Donald L. Jr.; Tipton, Alan R.; Lackey, Robert T. (Virginia Tech. Division of Forestry and Wildlife Resources, 1977)
    In this report, we develop a general theory of the relationship between life history and population structure for largemouth bass. In its most usable form the model is represented by a stochastic integral equation that is analogous to the classical Lotka model for age structure of populations. The corresponding differential equations can also be used successfully when closed-form solutions are available or when the phenotype dimension is low enough to permit numerical solution. Three general conclusions are presented. First, population dynamics may be appropriately viewed as a consequence of life history phenomena. This view suggests that, at least where prediction of population structure or where explanation of the phenomena is desired, such phenomena as density-dependence may be most appropriately described by analyzing effects of population structure and density on life history in the population. The second conclusion is that variation in life history may be important in determining population structure. Terms describing effects of variation are explicitly included in the model equations. The magnitude of these terms, however, is completely unknown for any life histories with which we are familiar. The third conclusion to be drawn is that population structure, at least averaged over time, should be fairly stable in large populations. Effects of variation in small populations, on the other hand, have not been analyzed and might be important.
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    A general population dynamics theory for largemouth bass fisheries
    Jester, Douglas B. Jr. (Virginia Polytechnic Institute and State University, 1977)
    Resolution of the main issues in largemouth bass management will require the ability to predict the effects of exploitation on population structure, optimally select size limits, relate bass population structure to prey population structure, and predict the effects of fluctuations in recruitment on production and yield. A general model of population structure was developed for use in studying these problems. The model was derived by examining the relationship between life history and population structure. Life history processes are described as mixed continuous and jump stochastic processes. The model was derived in two forms, an integro-differential equation and a stochastic integral equation, which include all of the classical continuous-time population models as special cases. Two general results concerning the model were proven. First, the stochastic integral equation was shown to predict the same expected population structure as a deterministic model using average birth and death rates whenever the processes are uncorrelated. However, it is very unlikely that birth rate, death rate, and density will be independent, so the stochastic and deterministic models will generally diverge. Second, it was shown that with density-independence the expected population structure in the stochastic model is asymptotically stable. Special cases of the model were used to illustrate the possible effects of exploitation on average catchability and population structure. Methods for calculation of optimal length limits and production and yield were illustrated for simple cases. Use of the full power of the model, however, must await more detailed description of factors influencing mortality and growth, especially the effect of the density and size structure of available prey.