Ecosystem Dominoes: Modeling Trophic Cascades and Keystone Species
An Interactive Ecology Inquiry for High School Learners
Materials Needed
- Physical Dominoes or Wooden Blocks (Jenga blocks work great): 10–12 blocks
- Color-Coded Index Cards or Sticky Notes: Green (Producers), Blue (Primary Consumers), Red (Secondary/Apex Predators), Yellow (Abiotic Factors)
- Large Poster Paper or Whiteboard: For mapping ecosystem connections
- Markers and Pens: At least two contrasting colors (e.g., Black for energy flow, Red for disruption)
- Ecosystem Scenario Cards: Included in lesson body (or printed)
- Digital Device with Internet Access (Optional): For quick species research
Lesson Overview & Objectives
| Target Audience: | High School / Grade 10 (Age 15) — Flexible for homeschool or classroom |
| Estimated Time: | 60 to 75 minutes |
| Core Subject: | Ecology / Environmental Science (Systems Thinking, Community Ecology) |
Learning Objectives
By the end of this lesson, the learner will be able to:
- Identify and define key ecological concepts: keystone species, trophic cascades, top-down control, and indirect interactions.
- Construct a visual trophic web model featuring at least 6 interconnected species across 3 trophic levels.
- Predict and justify the systemic impacts on an ecosystem when a key organism is removed or introduced, using evidence-based reasoning.
Success Criteria
- My ecosystem diagram correctly shows energy direction (arrows pointing from food to consumer).
- I can clearly explain how changing one population creates a ripple effect on at least two other species that don't directly interact with it.
- I can design a realistic ecological management proposal to fix a disrupted system.
1. Introduction: The Hook & Setup (10 Minutes)
The Hook Activity: The Falling Forest
Set up 5 dominoes in a straight line on a table, spaced so each falls into the next. Label each domino with a piece of tape/sticky note:
[Apex Predator: Sea Otter] → [Herbivore: Sea Urchin] → [Producer: Giant Kelp] → [Habitat: Fish Species] → [Coastal Protection: Shoreline Erosion]
Action: Flick the first domino ("Sea Otter removed by hunting"). Watch the whole line collapse.
Teacher / Educator Talking Points (Ages 15-appropriate)
"When most people think about nature, they picture simple linear food chains: grass gets eaten by deer, deer get eaten by wolves. But real ecosystems operate much more like complex engines or intricate software networks. If you pull out one single component, the entire system can reconfigure in ways you'd never expect."
"In the 1960s, an ecologist named Robert Paine literally pulled starfish off rock walls in Washington State and threw them into the ocean to see what would happen. He discovered that without that one starfish species, the whole community collapsed—mussels took over everything and total biodiversity plummeted. He coined the term Keystone Species. Today, we're going to dive into how ecosystems collapse—and how ecologists design solutions to rebuild them."
2. Body: Core Content & Guided Practice (45 Minutes)
Part A: Direct Instruction & Demonstration ("I Do") — 15 Mins
Concept Deep-Dive:
- Keystone Species: An organism that holds an entire system together, despite often having a relatively small overall biomass (like the wedge-shaped keystone at the top of a stone archway).
- Trophic Cascade: An ecological process that starts at the top of the food chain and filters all the way down to the bottom (or vice versa).
- Direct vs. Indirect Effects:
- Direct: Wolves eat Elk (Wolf population up → Elk population down).
- Indirect: Wolves eat Elk, so Elk stop lingering near riverbanks, which allows Willow trees to grow back, which brings Beavers back to build dams! (Wolf presence → Beaver boost).
Educator Modeling: Draw a mini-web on paper/board:
* Scenario: Orcas shift diet to Otters due to whale population decline.
* Result: Otters drop → Urchins explode → Kelp Forests get overgrazed → Fish nurseries vanish.
Part B: Collaborative Modeling ("We Do") — 15 Mins
Together with the student, build a interactive model on poster paper for the famous Yellowstone National Park Trophic Cascade.
Step-by-Step Instructions:
- Take green sticky notes for Producers (Willow Trees, Aspen, Riverbank Grasses). Place them at the bottom of the poster.
- Take blue sticky notes for Primary Consumers / Herbivores (Elk, Deer, Beavers). Place them in the middle.
- Take red sticky notes for Apex Predators / Secondary Consumers (Gray Wolves, Songbirds, Bears). Place them at the top.
- Draw black arrows showing Energy Transfer (e.g., Willow → Elk → Wolf). Note: Arrows point to the consumer!
- The Disruption Event: Place a red "X" over the Wolf note (representing their extirpation in the 1920s).
- Use a red marker to trace what happens to each node:
- Elk population increases (↑) and stays by riverbanks.
- Willow and Aspen trees get overgrazed (↓).
- Beavers have no wood for dams (↓). Songbird nesting sites disappear (↓).
- River banks erode, changing the physical shape of the river!
Part C: Independent Applied Challenge ("You Do") — 15 Mins
Task: "The Ecosystem Rescue Challenge"
Select ONE of the following real-world scenario cards below. Map the ecosystem on paper and answer the challenge prompts.
Option A: The Australian Out-of-Control Amphibian
Context: Invasive Cane Toads were introduced to control beetles in sugar cane fields. Instead, they produce toxins that kill native predators (Dingoes, Freshwater Crocodiles, Goanna Lizards).
Task: Map out toad, native predators, native insects, and smaller lizards. Predict what happens to the insect population when native predators die from eating cane toads.
Option B: The Vanishing Flying Foxes
Context: Flying fox bats on Pacific islands are major pollinators and seed dispersers for hardwood trees. Climate heatwaves and habitat loss are causing severe bat die-offs.
Task: Map bats, fruit trees, forest birds, and soil nutrients. Explain how a drop in bat populations impacts long-term forest growth and bird species.
Option C: The Local Prairie Dog Town
Context: Prairie dogs build complex underground burrows that aerate soil. They are eaten by Black-footed Ferrets, Hawks, and Coyotes. Ranchers often eradicate prairie dog colonies.
Task: Map prairie dogs, grasses, ferrets, burrowing owls, and soil quality. Explain why prairie dogs are considered a keystone species despite being seen as pests.
Student Deliverable for "You Do":
- Draw a 6+ node Food Web diagram.
- Write a 3-step cascading chain reaction that occurs during the ecological disturbance.
- Propose one management action an ecologist could take to stabilize this system.
3. Conclusion & Reflection (10 Minutes)
Summary Recap
Review the main takeaway: Ecosystems are interconnected non-linear networks. Removing or adding a keystone species causes domino effects (trophic cascades) that extend far beyond direct predator-prey pairs, altering abiotic features like rivers, soil quality, and climate resilience.
3-2-1 Reflection Exit Ticket (Verbal or Written)
- 3 key terms learned today and their definitions in your own words.
- 2 indirect connections you discovered in today's ecosystem models that surprised you.
- 1 real-world ecosystem in your local region or neighborhood that might have its own keystone species.
4. Adaptability & Differentiation Strategies
| Scaffolding (For Extra Support) | Extension / Advanced Challenge (For Heidi) |
|---|---|
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5. Assessment Options
Formative Assessment (During Lesson)
- Observation of arrow direction during the "We Do" mapping activity (ensuring learner understands energy flows from prey/producer to consumer).
- Verbal responses during the initial domino hook regarding direct vs. indirect effects.
Summative Assessment (End of Lesson)
Evaluate the student's Independent Challenge Worksheet/Poster using the simple benchmark below:
| Criteria | Proficient (3 pts) | Advanced (4 pts) |
|---|---|---|
| Web Accuracy | Includes 6+ species with correct energy flow arrows. | Includes 6+ species, correct arrows, and distinguishes direct vs. indirect links visually. |
| Cascade Analysis | Accurately predicts population shifts across at least 2 trophic levels. | Explains non-obvious indirect impacts, including impacts on non-animal factors (habitat/plants/soil). |
| Management Solution | Proposes a logical intervention to stabilize the ecosystem. | Proposes a creative, highly realistic intervention considering ecological trade-offs. |