Life tables: construction and interpretation

Life tables, which describe how the risk of death (and sometimes fertility) changes with age, are a fundamental tool for describing and exploring the diversity of life histories. Numerous important life history metrics can be derived from them. This chapter provides a broad coverage of life table construction and use and use with a particular focus on nonhuman animals. The calculation of life tables can be divided into approaches: cohort-based, where the data are obtained from individuals born at (approximately) the same time that are followed until death; and period-based, where the data are obtained from a population of mixed ages followed for a particular time-frame (e.g. a year). Worked examples of both approaches are provided using data from published sources. Emphasis is placed on understanding concepts such as rates vs. probability, life expectancy, and generation time. Links are drawn between the survivorship curve (type I, type II, and type III survivorship) and entropy. The chapter also covers the concept of the Lexis diagram which is used to represent births and deaths for individuals in different cohorts. Finally, the assumptions and limitations of life tables are discussed, with pointers to further reading. Code and data are provided.