Density-Dependent Rates of Population Growth: Estimation in Laboratory Populations

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Abstract
The fecundity of Drosophila in the laboratory depends on the levels of crowding during the larval stage. In addition, the function describing the number of adults produced by an initial number of eggs is not one-to-one. Consequently, the population dynamics determined from adult-to-adult transitions are likely to be biased (Prout and McChesney 1985). This result has called into question the general conclusion that laboratory populations of Drosophila have asymptotically stable population dynamics, since these observations were based on adult-to-adult transitions. Prout and McChesney''s own data seem to indicate that eigenvalues less than -1 may occur in laboratory populations of Drosophila. A reexamination of their data actually supports the notion that laboratory populations of Drosophila have stable dynamics. However, a thorough resolution of this question will require a determination of the population dynamics by observing changes in the numer of eggs. For populations of Drosophila kept in the serial-transfer system, it is shown that the two currently practiced methods for determining population stability are not equivalent. Since the method employing the mth-order difference equation (Mueller and Ayala 1981.alpha.) takes into account the complicated features of the serial-transfer system, it should be the preferred method.