Basic Analyses 1: Demographic Measures and Events in the Life Cycle

Abstract

A fitted IPM describes how a population as a whole changes in total abundance and in its size or state distribution. The case studies in Chapter 2 illustrated how the familiar measures of population change (stable population structure, long-term growth rate, reproductive value, etc.) can be calculated from an IPM. But the kernels that comprise an IPM also describe how individuals change in size or other state variables over their lifetime. In this chapter, we take a closer look at population growth, and then show how a fitted IPM can be used to calculate statistics summarizing the life cycle, such as age-specific fecundity and survival probability, expected lifespan, lifetime reproductive output, and size at death. For many of these it is also possible to calculate the expected variation among individuals that results just from chance events, such as the stochasticity of who lives and who dies in a given year, without any inherent differences among individuals.