The determination of key factors from life table data.

A new method is proposed for detecting key factors from life tables for animals whose life-cycle is divided into several stages. This method is based upon an equation that partitions the variance of the number alive at the end of the life-cycle into components associated with variation in the number entering the first stage of the cycle, variation in survival rates, and also density-dependent aspects of survival. It is illustrated by analysing Blank and Ash's (1962) census data for a population of partridges. The conclusions reached are somewhat different from those reached by Blank et al. (1967) when they applied Varley and Gradwell's (1960) type of key factor analysis to the same set of data.