Learning Objectives
11.4.1 Justify the use of life tables to determine population growth and size.
11.4.2 Describe how age or size structure influences population growth and population size.
11.4.3 Compare the three types of survivorship curves.
11.4.4 Analyze life table data and calculate a net reproductive rate (R0) and exponential growth rate (r).
Up to this point, we have assumed that individuals within a population do not vary in their birth (b) and death (d) rates. This is a big assumption given that we know real populations are made up of individuals of different ages, sizes, and sexes, which vary in their capacity to reproduce and survive. Information about the varying patterns of reproduction and survival in a population is essential if we want to understand current population growth or predict future population sizes. A life table provides a summary of how survival and reproductive rates vary with the age, size, or life stage of the individuals within a population. These summaries can then be used to predict future population trends and develop strategies for managing populations of commercial or ecological value. Before we explore life tables in more detail, let's first consider how populations can differ in their age and survivorship structure.