Chapter 1. Chapter 22: Community Ecology

1.1 Introduction

Welcome to the Interactive Study Guide for Chapter 22: Community 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 are keystone species in a community, and why are pollinators considered keystone species?
• What are food chains and food webs, and how does energy flow through them?
• What positive and negative interactions occur among members of a community?

1.2 Driving Question 1:

Why should you care?

A keystone species is one that plays a role in its community that is more important than would seem apparent by the size of its population. Bees are keystone species because of their role in pollination—the process of moving pollen (the minute male sexual stage of a flowering plant) from one flower to another. Bees are important pollinators for the crops that supply us with most of our food, fuel, and clothes. One in every three bites of food we eat is pollinated directly or indirectly by honeybees. You should care about keystone species because they are the ones whose existence is important for entire ecosystems. Healthy ecosystems protect the resources that you use.

Flowering plants (angiosperms) are the most diverse group of plants by far. For most of them, flowers serve as ways to attract pollinating animals to them, and the transfer of pollen by those animals is essential for fertilization and seed production. For pollination to occur properly, pollen must be transported from the stamen, where the pollen is produced, to the pistil, which contains the eggs that will become seeds, and which itself will become a fruit. Most plants will not produce seeds or fruits unless they are fertilized. Even if you never eat vegetables, your livelihood relies on flowering plants and therefore on pollinators.

What should you know?

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

1. Explain the concept of a keystone species.
2. Interpret information about the importance of bees and other pollinators to commercially important crops.
3. Describe the process of commercial crop pollination by bees.
4. Describe the steps involved in pollination.
5. Identify the parts of a flower.
6. Identify the parts of a fruit.
7. Explain the inter-relationship between pollinators and flowering plants.

Infographic Focus:

The infographics most pertinent to the Driving Question are 22.1, 22.2, and 22.3.

1.3 Driving Question 2:

Why should you care?

You should care about food chains because of your position in the food chain. Humans are consumers at the top of their food chain, meaning that we typically aren't eaten (thankfully!). Since energy is lost as it moves up the food chain from photosynthetic producers (in other words, plants), the higher we eat on the chain (in other words, the higher the trophic level), the more energy is required to feed us.

You should care about food webs because humans too often fail to see how most things are connected to each other. Individual organisms in the food web have multiple important roles that keep the community healthy.

What should you know?

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

1. Name the terms used to describe different trophic levels in a food chain, and explain how they obtain energy.
2. Trace the flow of energy through trophic levels.
3. Explain how much energy is transferred between trophic levels.
4. Describe the interconnections between members of a food web.

Infographic Focus:

The infographics most pertinent to the Driving Question are 22.4 and 22.5.

1.4 Driving Question 3:

Why should you care?

As mentioned in previous chapters, you are actually a collection of organisms living together—human cells plus bacterial cells both benefitting from each other—a form of mutualism. Humans may be host to other kinds of organisms like archaea or even arthropods. For example, most people harbor populations of harmless mites that live off the dead cells from our skin or hair but do no harm to us—an example of commensalism. Organisms living with us that gain benefit while harming us are employing parasitism. Hardly any organism truly lives alone.

Different pollinators are attracted to different kinds of flowers, and many flowers are specialized for specific pollinators. The different kinds of flowers provide a niche for those pollinators. The competitive exclusion principle is the hypothesis that two species can't rely on an identical niche because one will always prevail. In other words, two pollinators couldn't coexist if they pollinated exactly the same species of flowers.

Bees are just an example of the many groups of organisms that compete for similar niches and resources. They are also examples of a group in which there are native and non-native organisms living together and competing with each other. Honeybees, which are from the Eastern Hemisphere, have threatened bees native to North America by competing with them for resources (flowers) since they were brought here by European settlers. Now, honey bees are threatened by their more aggressive cousins, Africanized honeybees.

What should you know?

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

1. Compare and contrast three different kinds of symbioses: mutualism, parasitism, and commensalism.
2. Explain how characteristics of a flower create ecological niches for the pollinators it attracts.
3. Describe three different ways that species with similar ecological niches compete for the same resources.

Infographic Focus:

The infographics most pertinent to the Driving Question are 22.6, 22.7, 22.8, and 22.9.