9: The Ecology of Populations

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Learning Objectives

Define what ecologists mean by a population of organisms and the focus and scope of the science of population ecology.
Introduce the key features of populations studied by ecologists, wildlife biologists, and conservation biologists -- such as size, density, and range -- and the field methods used to study them.
Outline common patterns of population change, such as growth, extirpation, extinction, and cycles.
Introduce the concepts of population regulation, density independence, and density dependence.

9.1: What is population ecology?
Ecology is often defined as the study of the distribution and abundance of organisms. Population ecologists study what determines the occurrence and abundance of species in space and time: their geographic ranges, population sizes and densities, what factors result in them being so rare or common, and why these characteristics change over time.
9.2: Population Ecology Research Methods
There are many ways to quantify the occurrence, density, and absolute population size of populations. This section highlights some of the more commonly used methods to study populations.
9.3: Population Dynamics and Regulation
Changes in population size over time and the processes that cause these to occur are called population dynamics. How populations change in abundance over time is a major concern of population ecology, wildlife ecology, and conservation biology. The processes and mechanisms that drive population change include competition, the availability of food or other resources, extreme weather, inbreeding, predators and parasites.
9.4: Scientist Spotlight - Jessie Isabelle Price

Summary

Populations are one of the major levels of biological organization, and "population thinking" has played a key role in ecology and evolutionary biology since Darwin. Currently, many researchers and natural resource managers are trained as population ecologists, from academics who study basic questions in evolutionary ecology to government scientists who determine catch limits for fisheries. In this chapter we define what populations are, their key features which are considered by basic and applied ecologists, and the techniques used out in the field to study populations. We'll also introduce key ecological concepts which will be elaborated on in the next chapter, including population regulation, density independence, and density dependence.