Prediction of Population Growth Form in Daphnia pulex Cultures

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Abstract
From previously assembled data on age and density-specific birth, death and growth rates of Daphnia grown under controlled conditions, it is possible to make predictive estimates of population growth form, given an initial density and age distribution. Six alternative models are tested. Four consider birth and death rates as functions of numbers in population. Others treat these rates as related to biomass as well as numbers. Analytical data indicate that a 5 day lag exists between occurrence of a certain density and its effect on birth rate. Two models take this lag into account; others do not. All models involve simplifying assumptions. Different models predict widely disparate population peak values. One model expected a priori, to provide the best approximation of population growth is the only one that does provide a fair fit to observational data. Information required for successful prediction according to this scheme is much too large to make it feasible for natural populations of animals with present knowledge. Wide differences that exist between different predictions emphasize that demographic features can not be neglected in studies of population growth form.