Introduction

In this chapter's Case Study, we focused on a fundamental ecological question: What determines the distribution and abundance of a species, in this case kelp? The distribution of a species is simply the geographic area where individuals of the species are present, while its abundance refers to the number of individuals of a species or population.

Determining the distributions and abundances of species, and the factors important to these patterns, can be challenging given that groups of individuals (or populations) often vary dramatically over space and time. Our ability to document this variability and predict these changes can serve as a “measuring stick” for how well we understand events in nature. In this chapter, we will focus on how and why the distribution and abundance of individuals within species and populations vary over the landscape and ways in which to measure that variation. In Chapters 10 and 11, we'll expand our view of populations by considering how they vary over time using both examples and population growth models. But first, we'll begin by describing aspects of populations and individuals, including estimations of abundance, in more detail.