Chapter 1. Chapter 21: Population Ecology

1.1 Introduction

Welcome to the Interactive Study Guide for Chapter 21: Population Ecology! This Study Guide will help you master your understanding of the chapter's Driving Questions, using interactive Infographics and activities, as well as targeted assessment questions. Click "Next" to get started, or select a Driving Question from the drop-down menu to the right.

DRIVING QUESTIONS

• What is ecology and what do ecologists study?
• What are the different patterns of population growth?
• What factors influence population growth and population size?

1.2 Driving Question 1:

Why should you care?

The study of ecology is becoming increasingly important as concern grows about the effect of environmental degradation not only on human health and well-being but also on the well-being of all species that call Earth home. Ecology is studied at many levels; understanding the levels of ecology will help you understand and interpret ecological information.

Have you ever looked at an aerial photo of North America at night? If you have, you might have noticed that there is an interesting pattern of lights: all of the coasts are outlined; there’s a scattering of lights throughout the eastern half of the continent; and most of the western interior is dark. The superficial reason for this pattern is immediately apparent—the lights indicate where the biggest populations of people live. But the deeper questions of what historical, cultural, economic, and geographical factors have caused this distribution of people are much more complex. Just as a sociologist might want to study the distribution of people, ecologists often need to study the distribution pattern of various organisms; they tailor their studies to the nature of the organisms so that they can learn the right questions to ask about why those organisms live where they do.

Understanding how organisms distribute themselves reveals how they interact. Think again of human interactions—how would four strangers arrange themselves in an elevator? Would you expect them to bunch up in the same corner or to distribute themselves uniformly into each corner of the space? People tend to want to give each other space in close quarters. If you increase the scale, however, to human interactions at the neighborhood or town level, you will see that their distribution tends to be clumped: there are subdivisions, apartment complexes, and townhouses. This tends to be because of the distribution of suitable land for housing, the need for utilities, and zoning restrictions. Just as there is much to learn from the way people arrange themselves, there is much to learn about the way other organisms are distributed.

What should you know?

To fully answer this Driving Question, you should be able to:

1. Explain the nested levels of ecology.
2. Explain how distribution patterns may affect population sampling methods.
3. Explain the difference between random, clumped, and uniform distribution patterns.
4. Explain what factors cause distribution patterns.

Infographic Focus

The infographics most pertinent to the Driving Question are 21.1 to 21.3.

1.3 Driving Question 2:

Why should you care?

All populations grow, and all have upper limits to their size—including human populations. The global human population has been growing exponentially for the last century, and evidence suggests that we are approaching the upper limit of sustainable population. Learning about population growth and carrying capacity in other organisms will help you understand what humans are facing.

What should you know?

To fully answer this Driving Question, you should be able to:

1. Compare and contrast exponential and logistic population growth.
2. Understand how population growth rate is calculated.
3. Define and explain the role of carrying capacity in the growth of populations.

Infographic Focus

The Infographic most pertinent to the Driving Question is 21.4.

1.4 Driving Question 3:

Why should you care?

A central truth in ecology is that everything is connected. We often forget that we are part of nature, not outside of it. Just as ants modify their environment by building colonies, we modify our environment by building cities. The level and complexity of the ways we change the world to suit our purposes may be greater than that of most animals, but we are still animals living in and affecting nature. Realizing that we are still connected to the environment is important.

For populations of predators like the wolves on Isle Royal to survive, they must have an adequate supply of prey. If they were to eat all the moose and other prey animals on the island, they would die out. Instead, populations of wolves and moose periodically fluctuate, maintaining an equilibrium.

Both living and nonliving conditions can influence the populations of an organism, whether they are wolves, trees, moose, or people. For humans, abiotic factors that affect population growth are natural disasters, climate, and availability of resources like clean water. Biotic factors include diseases, birthrates, and death rates.

Global climate change is recognized by most scientists, especially ecologists, and ecologists are especially concerned about the effects of changing climate on ecosystems. Why should you care? Some of the predicted effects include the proliferation of organisms that spread disease, such as mosquitoes that carry malaria.

What should you know?

To fully answer this Driving Question, you should be able to:

1. Interpret fluctuating patterns of prey and predator populations over time.
2. Explain the inter-relationship between wolf population size, moose population size, and tree growth at Isle Royale.
3. Explain the various ways the health of moose and wolves can be assessed indirectly from their scat, urine, and blood.
4. Explain how abiotic and biotic factors influence wolf and moose population size.
5. Differentiate between density-dependent and density-independent influences on wolf and moose population sizes.

Infographic Focus

The infographics most pertinent to the Driving Question are 21.5 to 21.9.