Extended Life Table

Abstract

Life table analysis of studbooks combines mortality and fecundity data in a single table. This table is named in this book “extended life table” to avoid confusion, as life table can also refer to mortality data alone. This chapter shows methods of estimating net reproductive rate (R ₀), generation time ($\bar{T}$) and intrinsic rate of increase (r) from age–specific mortality and fecundity rates. The method to calculate Fisher’s reproductive value (V _x ) is described. This measure refers to the number of expected future offspring (of the same sex) produced by an individual of a given age that is weighted against population growth. The unweighted value is used as a measure of fitness. The age distribution of a population that is growing geometrically with constant mortality and fecundity rates will gradually approach a fixed or stable age distribution. The proportion of individuals in different age classes can be estimated from age–specific survivorship (l _x ) and the finite rate of increase (λ). The use of midpoint survivorship (L _x ) to estimate the proportional number of births in species that breed all year round (birth–flow) is discussed. The last section of this chapter compares life tables and census data to estimate population growth.