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How Well Does the Edmonson‐Paloheimo Model Approximate Instantaneous Birth Rates?

Lynch, Michael
Ecology 1982 v.63 no.1 pp. 12-18
Daphnia pulex, age structure, analysis of variance, birth rate, eggs, equations, factor analysis, models, mortality, seasonal variation, variance, zooplankton
An equation independently derived by Edmondson and Paloheimo for estimating instantaneous birth rates without a knowledge of mortality rates has been extensively employed by zooplankton ecologists. This expression is exactly true only under the unlikely conditions that the age distribution is stable and that egg mortality is equal to that averaged across the entire population. Here I compare estimates of instantaneous birth rates (b) using the Edmondson—Paloheimo equation to those determined with a general model which accounts for age structure instability and egg mortality in two Daphnia pulex populations. Despite the fact that the assumptions of the Edmondson—Paloheimo models are rarely met, it mimics the seasonal pattern of b quite well, with few exceptions. An analysis of variance suggests that the model will provide an adequate approximation of the true population birth rate when a variance in b of 0.003 can be tolerated. A much more critical factor in the analysis of instantaneous rates in plankton populations is the development of accurate sampling techniques.