Introduction
The pattern of growth of a population is determined by the temporal pattern of the organism’s reproduction and mortality. Some species have discrete generations that do not exist simultaneously. For example, annual plants germinate, grow, flower, and set seed in one year. All the adults die and a new generation arises from seed the next year. In other species the generations overlap—individuals may breed more than once per season and some individuals survive to reproduce again in another season. In these species offspring may coexist with their parents—the generations overlap.
We use different mathematical approaches to describe the growth of species with discrete and overlapping generations. Populations with discrete generations can be described by geometric growth equations. Populations with overlapping generations are best described by equations for exponential growth. In this exercise you will explore the difference between these two models of population growth.
Learning Goals
After reading your text and completing this exercise, you should be able to:
- Explain the variables used in geometric and exponential growth equations.
- Understand how geometric and exponential equations describe population growth.
- Discuss the difference in the pattern of population growth over time for populations with discrete and overlapping generations.
- Explain how the growth curves are affected by the time scale of the graph, the initial population size, and the reproductive rate.