Link back to the Teacher’s Guide Table of Contents

Unit 8 Teacher’s Guide Table of Contents

  1. Topic 8.1: Response to the Environment/Animal Behavior
  2. Topic 8.2: Energy Flow in Organisms and Ecosystems
  3. Topics 8.3 – 8.5: Population Ecology and Community Ecology
  4. Topics 8.6 – 8.7: Biodiversity and Disruptions to Ecosystems

Essential Links

  1. The College Board’s AP Bio Course and Exam Description.
  2. My Condensed Version of the Course and Exam Description: takes the objectives, Enduring understandings, and key ideas of the 230-page CED and renders it into 40 pages.
  3. My AP Exam Review Outline: Takes the Course and Exam description and renders it into student (and teacher) friendly language.
  4. 2023-24 AP Bio Scope and Sequence Calendar: A spreadsheet that lays out the entire course.

Topic 8.1: Response to the Environment (Animal Behavior)

Teaching objectives for Topic 8.1, Responses to the Environment

Topic 8.1 covers some of the best stuff in biology. But if you’re like me, you’ll find that examining the College Board’s objectives in their Course and Exam Description won’t give you the clearest guidance about what to teach. That’s because these learning objectives start with exclusion statements that discourage us from diving into the specifics.
  • In relation to how changes in the environment are related to physiological or behavioral changes, no specific physiological mechanism is required.
  • In relation to communication and behavioral systems, the details of these systems are outside the scope of the exam and course.
On top of that, the learning objectives are very general. Here’s my summary of what you’ll find on the CED. 
  1. Based on cues in the environment, organisms change their behavior and physiology.
  2. Communication between organisms in response to internal or external changes can change behavior.
  3. Signaling changes the behavior of other organisms and is subject to natural selection.
  4. A variety of signals (visual, auditory, tactile, chemical, and electrical) are used to indicate social dominance, find food, and induce or solicit mating.
  5. Learned and innate behaviors are subject to natural selection.
  6. Cooperation between members of the same population can increase fitness.

So, what I chose to do on is to focus on some important biological literacy goals that will also help our students as we get them ready for the AP Bio exam. We want our students to be able to explain 1) how animal behavior can be elicited in response to environmental cues, 2) how animals communicate with one another, and  3) how animal behavior is optimized by natural selection. And, on top of that, being able to analyze sets of data and diagrams related to animal behavior is something that shows up pretty frequently on the AP Bio exam.

Holding all that in mind, here’s what I came up with. There’s a strong emphasis on case study analysis.

Teaching about Responses to the Environment on

Our module on animal behavior covers this material in four tutorials. You can find the main menu on this page.

Fixed Action Patterns and Behavior Genes

Fixed action patterns are “hard-wired” behaviors found in many animals (including humans). These patterns were first discovered by the Dutch Ethologist Niko Tinbergen. Once your students learn about these, we move on to the evidence that certain behaviors can be genetically encoded. This takes us into foraging behaviors in Drosophila larvae, nest-building behavior in mice, and parental care in voles. In these rodents, the concentration of a certain hormone seems to determine whether fathers are monogamous or promiscuous. In the case study, there’s a discussion of a Partner Preference test which is fascinating in its own right but also linked to the AP Bio choice chamber lab (discussed below).

Learning and Orienting

In this tutorial, we move from hard-wired behaviors to ones that involve learning. The first of these is imprinting, first discovered (and hilariously manipulated) by Austrian zoologist Konrad Lorenz. This is followed by an analysis of much more complex learned behaviors: learning songs in songbirds, and navigation in wasps. The tutorial ends with an unbelievably cool study of how ants know how to make their way back to the nest after foraging. This is known as the ant odometer, and you don’t want to miss it.


This tutorial examines the internal and external cues that animals use during migrations. In the first case study, we focus on how Indigo buntings navigate by learning how to follow the stars. In the second, we look at how sea turtle hatchlings are able to first find their way to the sea. Once the turtles make it out to sea, they face the challenge of long-distance migrations (that often span thousands of miles). To do that, they use magnetoreception and perception of geomagnetic signatures to find their way back to the beaches where they originally hatched. I found this to be mind-blowing when I first learned about it. My guess is that your students (and you) will feel the same.

Living in Groups

The module ends with a tutorial about group behavior and its biological basis. The first case study looks at alarm calls in Belding’s ground squirrels. Who do you think gives alarm calls first: males or females? Why would that be? What you’ll see this that this study is a great way to get into the concept of kin selection and inclusive fitness. This leads to a look at haplodiploidy in bees, and how that can explain the social structure of a bee hive. We end with a discussion of honey bee dances, and how bees use their dances to communicate about the direction and distance to food sources to other members of the hive.

Additional Resources

In the AP Biology Lab Manual, you can find the “Fruit Fly Behavior Lab” (investigation 12). I use a much simpler (and less expensive) version of this lab. My version involves pill bugs (Armadillium vulgare), which you or your students can probably find in any park (or backyard). If students collect 10 each, you’ll have more than enough. I have a set of choice chambers that I bought from Carolina biological supply, but you can have your students construct their own by cutting out the bottom of two milk cartons, cutting out a notch to make a pathway between them, and then scotch taping them together. Then just lay a paper towel that’s cut to size on the bottom of each carton and you’ll be set.

Here’s a link to my version of the lab. I’m sure it can be improved. And just to prove to myself that it could be done, I just spent about 10 minutes putting together a milk-carton choice chamber. Here’s a photo.

Topic 8.2: Energy Flow Through Ecosystems

Learning objectives for Topic 8.2, Energy Flow through Ecosystems

Here are the College Board’s objectives for Topic 8.2 rendered into a much friendlier format.

  1. Compare and contrast endotherms and endotherms.
    • Endotherms use thermal energy generated by metabolism to maintain homeostatic body temperatures.
    • Ectotherms lack efficient internal mechanisms for maintaining body temperature. Their temperature can fluctuate widely, though they may regulate their temperature behaviorally by moving into the sun or shade or by aggregating with other individuals.
  2. Describe the relationship between metabolic rate and size.
    • Generally, the smaller the organism, the higher the metabolic rate.
  3. Describe the relationship between energy gain or loss and growth/survival/reproduction
    • Net energy gain results in energy storage or the growth of organisms or populations.
    • Net energy loss results in loss of mass, death, and population decline.
  4. Describe how energy flow through ecosystems can be graphically represented.
    • Through food chains, food webs, and energy pyramids.
  5. *Define biogeochemical cycle, and (as a representative example) explain the carbon cycle.
  6. Explain the effects of changes in energy availability on trophic levels and ecosystem structure.
    • Changes in energy availability can affect the number and size of the trophic levels. Specifically, a change in the producer level can affect the number and size of other trophic levels.
  7. Compare autotrophs and heterotrophs
    • Autotrophs capture energy from physical or chemical sources in the environment;
    • Heterotrophs capture energy by eating or absorbing chemical energy in organic compounds.
  8. Compare photoautotrophs with chemoautotrophs
    • Photoautotrophs use light to synthesize organic compounds. Plants, algae, and cyanobacteria are photoautotrophs.
    • Chemoautotrophs power the creation of organic compounds by oxidizing small inorganic molecules (such as iron). This process can occur in the absence of oxygen. All chemoautotrophs are bacteria or archaea.

Teaching about Energy Flow through Ecosystems on

Topic 8.2 Part 1: Energy Use in Organisms

This tutorial starts by clarifying the ways that autotrophs, heterotrophs, and chemoautotrophs derive energy from the environment to sustain their life processes.

This leads to a general discussion of metabolic rate, and the way in which energy use scales with size, as shown in the graph below

That makes sense, right? You’d expect that the energy required to sustain an elephant would be much more than the energy required to sustain a smaller animal (like a pig) or a mouse.

But what’s fascinating is that as an animal’s mass increases, its metabolic rates/gram of tissue decreases. A gram of tissue in a shrew (the smallest mammal) is burning through energy a million times faster than a gram of elephant tissue does. When graphed, that relationship looks like this:

The reasons for this are largely (but not entirely) related to surface area: volume ratios and this topic will give you a great opportunity to do some review of topic 2.3 (Surface Area and life). For a deeper dive into this material, I strongly suggest that you read this archived article from the NY Times (from 1999: no subscription needed).

The tutorial ends with a discussion of metabolic differences between endotherms and ectotherms, and adaptations that occur in both groups related to optimizing energy use.

Topic 8.2, Part 2: Carbon Cycle

It’s hard to imagine teaching about ecosystems at the AP/Introductory college level without teaching about biogeochemical cycles. But the term “biogeochemical cycle” doesn’t appear anywhere in the 2019 Course and Exam Description. Nor does the term “carbon cycle.” Oversight? Hard to know. My first tutorial focuses on … the Carbon Cycle. It’s pretty easy, and I can’t imagine sending my students out into a world where the number 1 issue is climate change caused by disruption of the carbon cycle without them understanding the carbon cycle. I hope you feel the same way.

Topic 8.2, Part 3: Food Chains and Food Webs 

This tutorial will teach your students about autotrophs, heterotrophs, food chains, food webs, and the basics of trophic levels.

Topic 8.2, Part 4: Trophic Levels

This tutorial goes into depth about trophic levels and will take your students through energy pyramids and the 10% rule. Pyramids of numbers and biomass are also covered.

Additional Resources

As I said above, it’s not clear if the Carbon Cycle is part of the curriculum anymore. But if you teach it, I have a music video for you. I also have one about food chains. My Food Chains Song is one of the only songs I’ve written to someone else’s melody. It’s based on the Ballad of Jed Clampett, also known as the “Beverly Hillbillies Song.” Both songs are immensely singable (and playable on guitar). Here are the links.

  1. Carbon Cycle
  2. Food Chains Song

I can’t share the links for the next two items directly (because they’re copyrighted material) but the high school biology POGILS on “Energy Transfer in Living Organisms,” and “Ecological Pyramids are both excellent and highly recommended.

HHMI has a terrific video about how aquatic food webs in rivers can be studied. In addition, there’s an HHMI card-sort activity about modeling food webs in a tropical rainforest ecosystem.

Topics 8.3 – 8.5: Population Ecology and Community Ecology

Learning objectives for Topics 8.3-4 (Population Ecology) and 8.5 – 6 (Community Ecology and Biodiversity)

If you want to look at the College Board’s objectives for these topics, the links are above. Here’s an outline of how I cover this material on

Population Ecology

  1. Explain the general factors behind population growth, and the general equation for this growth  (dN/dt = B – D)
  2. Explain what exponential growth is and when it occurs, and be able to use its relevant equation (dN/dt = rmaxN)
  3. Define limiting factors.
  4. Compare and contrast Density Dependent and Density Independent Limiting Factors
  5. Define carrying capacity.
  6. Be able to use the Logistic Growth equation (dN/dt = rmaxN (K-N/K))
  7. Explain how population growth can be influenced by resource availability and predator-prey interactions.

Community Ecology

  1. Describe the key Interactions that occur between the species in a community. This includes the following interactions and being able to describe the positive and negative effects on each species.
    • Mutualism
    • Parasitism
    • Commensalism, amensalism
    • Competition (leading to niche partitioning and character displacement)
    • Predator/Prey interactions (leading to evolutionary arms races)
  2. Explain what keystone species are, and what happens when keystone species are removed from their ecosystems.
    • An organism whose activity defines the structure of the entire ecosystem.
    • Often these are carnivores that control herbivores, increasing productivity and overall biodiversity.
    • When keystone species are removed, ecosystems can collapse.
  3. Explain how communities change over time during the process of ecological succession.

Teaching about Population Ecology and Community Ecology on

Here’s how I cover the objectives listed above.

Topics 8.3-8.4: Population Growth

This tutorial teaches exponential growth and logistic growth. This includes limiting factors, carrying capacity, predator/prey-related population oscillations,  and r v. K selection.

Topic 8.5, Community Ecology, Part 1: Species Interactions

This first community ecology tutorial starts with a discussion about niches and habitats. It then runs your students through the gamut of species interactions (mutualism, parasitism, commensalism, amensalism, predation, herbivory, and parasitoidism).

Two of these interactions receive special attention. The section on competition is expanded to include competitive exclusion, niche partitioning, character displacement, and realized v. fundamental niches. A section on evolutionary arms races gets students to take a closer look at the consequences of predator/prey and parasite/host interactions.

Topic 8.5, Community Ecology, Part 2: Keystone Species and Trophic Cascades

This second community ecology tutorial looks at keystone species and trophic cascades. I built this tutorial around the HHMI video “Some Species are More Equal than Others.”

Topic 8.5, Community Ecology, Part 3: Ecological Succession

The term “ecological succession” doesn’t appear in the College Board’s Course and Exam Description. I can’t imagine teaching a unit on ecology without teaching this concept. But if you have to skip a tutorial because you’re running out of time, then this would be the one to skip.

Additional Resources

Flinn’s High School level POGIL on Population gives great reinforcement of exponential and logistic growth.

Topics 8.6 and 8.7: Biodiversity and Disruption to Ecosystems

Learning objectives for Topic 8.7 (Disruptions to Ecosystems)

If you want to look at the College Board’s objectives for these topics, you can do so on my condensed outline (the link is above). Here’s how I’ve rendered these objectives into a form that’s easier for you and for your students
  1. Define Biodiversity, and describe its key components.
    • Species composition and richness.
  2. Know how to use Simpson’s Biodiversity Index.
  3. Explain the connection between biodiversity and ecosystem resilience.
    • Less biodiversity and less ecosystem complexity often equate to less resilience to environmental change.
  4. List and describe the traits that predispose a species to become an invasive species.
    • High reproductive rates, tolerance of a wide range of conditions, generalist ecological niche.
  5. Explain how invasive species affect ecosystem dynamics and biodiversity.
    • When invasive species enter a new habitat, they tend to grow exponentially.
    • As invasive species are freed from control by their former predators or competitors, they can outcompete or overexploit the species in their new environment, or overrun their new habitat.
    • The overall effect is a decrease in biodiversity.
  6. Describe the human activities that lead to changes in ecosystem structure and/ or dynamics.
    • Destruction or degradation of habitat, habitat fragmentation, the introduction of invasive species,
    • The introduction of new diseases can devastate native species.
    • Climate disruption is altering habitats worldwide.
  7. Explain how geological and climatic changes can change ecosystem structure and/or dynamics.
    • Changes in geology and climate can alter habitats and change ecosystem distribution.

Topic 8.6: Biodiversity

This tutorial looks at the three dimensions of biodiversity (genetic, species, and ecological). As a preview of the last topic of the course (ecosystem disruption) I provide an overview of biodiversity’s importance. The tutorial ends by looking at how biodiversity can be measured and walks students through how to understand and use the Simpson Biodiversity Index.

Topic 8.7: Disruptions to Ecosystems

The tutorial starts by setting the stage. We’re in what’s widely regarded as the Anthropocene Age: humans have become the dominant biological and geological force on the planet. One of the main consequences of our preeminence is the Sixth Extinction (the fifth was when the dinosaurs were wiped out 65 million years ago). If you haven’t read Elizabeth Kolbert’s book The Sixth Extinction, then you should put it on your summer reading list. If you can’t make that happen, then you can read Kolbert’s 2009 article about the sixth extinction in the New Yorker.

I follow this introduction with an excerpt about the unique biological role of humanity from what might be a surprising source: one of my favorite movies, The Matrix. I’m curious about what you think about this section. Is it useful? Something students can relate to? If you have an opinion, use the “Contact” menu to send me an email and let me know.

After setting the stage, the rest of the tutorial runs through the major ways that humans have disrupted ecosystems. These include

  1. habitat destruction
  2. habitat fragmentation
  3. overharvesting/overhunting
  4. spreading invasive species

The tutorial ends with measures that we can take as a species to protect other species. This includes some large-scale moves (controlling human population growth, moving from fossil fuels to renewable energy), but also some smaller-scale things such as

  1. strategies for bringing endangered species back from the edge,
  2. principles for the design of nature reserves (it’s all about maximizing quality habitat and avoiding population bottlenecks for the species within the reserves),
  3. Focusing on biodiversity hotspots.

HOLY COW. That’s the end of the course! Congratulations.

Additional Resources

  • Flinn’s POGIL on Eutrophication gives a nice window into ecosystem disruption through changing nutrient cycling. This tutorial fits well with one of the objectives in Community Ecology (ENE-4.B.2: Interactions among populations determine how they access energy and matter within a community).
  • HHMI’s Lionfish Invasion is a great way to tie together invasive species with a review of population growth models.

Unit 8 Cumulative Objectives, Flashcards, and Quizzes

To pull together Unit 8, use the AP Bio review materials (flashcards, MC Quizzes, Practice FRQs, and click-on challenges) on Your students can access these same materials on the Biomania AP Bio app, and results from both are recorded in your teacher dashboard.

As always, you’ll want to use the progress check questions for Unit 8 on AP Classroom.