Confidence intervals for population growth rate of organisms with two-stage life histories

Although life histories can be modelled with great generality using project ion matrices, for organisms with life histories that can be accurately desc ribed by a simplified set of parameters, e.g. when adult Fecundity and mort ality are independent of age, more accurate estimates of life table paramet ers and of population growth rate and its standard error can be readily obt ained. Here an analytic method for calculating approximate confidence inter vals for population growth rate is given for two-stage life histories that can be described by Four variables representing age at first breeding? fecu ndity per unit time; and juvenile and adult survivorships per unit time. Th e method is applied to experimental data on Capitella sp. I obtained by Han sen et al., and quite good agreement is found between the analytic and boot strap estimates of the standard error of lambda. The analytic estimates wer e a little conservative, probably because of the way the action of mortalit y was modelled. Alternative life-history models are briefly discussed, and the desirability of Formulating life-history models so that the variables i nvolved are independent of each other is stressed. Analytic estimates of la mbda may be biassed if an inappropriate model is chosen or if variables are not independent and the correlations between them are not measured. To all ow for these possibilities, where necessary a conservative approach should be taken to significance testing using the analytic method.