Week 1: Ecosystem Dynamics & Trophic Cascades
Grade 7 Science | Rosche | Kairos Academies
NGSS Standards Covered This Week
MS-LS2-4 (NEW this cycle)
What it means: Construct an argument supported by empirical evidence that changes to physical or biological components of an ecosystem affect populations.
In student language: I can explain how changing one part of an ecosystem (like removing wolves) affects everything else.
Spiral Standards from Previous Cycles
- MS-ESS1-4 (Cycle 7): Geologic time scale - how ecosystems recover after mass extinctions
- MS-ESS3-3 (Cycle 4): Human impact on the environment
The Phenomenon: Wolves Changed Rivers
When wolves were hunted to extinction in Yellowstone by 1926, something unexpected happened over the following decades:
- Elk populations exploded without wolf predation
- Riverbanks were overgrazed as elk ate all the willows
- Rivers widened and meandered without plant roots to stabilize banks
- Beavers disappeared because they had no willows for food or dam-building
Then in 1995, 14 wolves were reintroduced. Within 20 years, the rivers literally changed course!
Focus Question: Why did removing wolves from Yellowstone change the rivers?
Learning Targets & Success Criteria
By the end of this week, you will be able to:
Target 1: Explain how energy flows through trophic levels
Self-check: Can I trace energy from producers to apex predators using the 10% rule?
Target 2: Model cascading effects through food webs
Self-check: Can I predict what happens to willows when wolves are removed?
Target 3: Predict ecosystem changes from species removal/addition
Self-check: Can I explain why removing a keystone species has bigger effects than removing other species?
Target 4: Design interventions for ecosystem restoration
Self-check: Can I create a plan to restore an ecosystem using trophic cascade principles?
Vocabulary
Practice These Vocabulary Terms
Watch First:
Search YouTube for "How Wolves Change Rivers" (4:30 video) or read the description in the phenomenon section above.
COMPLETE THE HOOK FORM BELOW
Submit your predictions before moving to Station 1.
[EMBED G7.C8.W1 Hook Form Here]
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Worked Example and Simulation
Simulation: Trophic Cascade
PREDICT (before running the sim)
Look at the simulation controls. Before changing any
variables, predict what will happen when you adjust them. Write your
prediction down.
OBSERVE (while using the sim)
Change one variable at a time. Record what happens after each change.
Use the data journal to capture at least 3 trials.
EXPLAIN (after collecting data)
Compare your observations with your prediction.
Use scientific vocabulary to explain the patterns you
found. What surprised you? What confirmed your thinking?
Problem Scenario
In 1995, scientists reintroduced 14 wolves to Yellowstone National Park after a 70-year absence. Over the next 25 years, the entire ecosystem transformed — not just the animals, but the trees, the rivers, and even the shape of the landscape. Use the simulation below to explore this trophic cascade, then follow the expert thinking process.
Explore: Yellowstone Trophic Cascade Simulation
The simulation will ask you to predict what happens, then let you watch, then ask you to observe and explain. This is the Predict-Observe-Explain (POE) strategy scientists use.
Key Vocabulary (5
terms) —
Practice Tool
Simulation: Trophic Cascade
PREDICT (before running the sim)
Look at the simulation controls. Before changing any variables, predict what will happen when you adjust them. Write your prediction down.
OBSERVE (while using the sim)
Change one variable at a time. Record what happens after each change. Use the data journal to capture at least 3 trials.
EXPLAIN (after collecting data)
Compare your observations with your prediction. Use scientific vocabulary to explain the patterns you found. What surprised you? What confirmed your thinking?
Problem Scenario
In 1995, scientists reintroduced 14 wolves to Yellowstone National Park after a 70-year absence. Over the next 25 years, the entire ecosystem transformed — not just the animals, but the trees, the rivers, and even the shape of the landscape. Use the simulation below to explore this trophic cascade, then follow the expert thinking process.
Explore: Yellowstone Trophic Cascade Simulation
The simulation will ask you to predict what happens, then let you watch, then ask you to observe and explain. This is the Predict-Observe-Explain (POE) strategy scientists use.
Mississippi River Ecosystem: Our Local Trophic Cascade
Just like wolves in Yellowstone, beavers were removed from Missouri rivers in the 1800s for fur trade. The result? River landscapes changed dramatically—less flooding control, fewer wetlands, different fish populations. Scientists like Dr. Karen Frey (University of Minnesota geographer) study how removing keystone species changes entire ecosystems. Dr. Frey's work on climate impacts shows that Missouri's rivers face similar cascade effects when species disappear. Understanding trophic cascades helps us restore local ecosystems—beaver reintroduction projects are happening across Missouri right now, bringing back wetlands that filter pollution and prevent floods.
Step-by-Step Problem Solving
Station 1 – Trophic Cascade Simulation
20 Points | ~18 Minutes
COMPLETE THE STATION 1 FORM BELOW
Run at least 2 scenarios in the simulation before answering!
[EMBED G7.C8.W1 Station 1 Form Here]
Form ID: ________________
Station 2 – Population Dynamics Analysis
20 Points | ~15 Minutes
COMPLETE THE STATION 2 FORM BELOW
Reference the data table above while answering the questions.
[EMBED G7.C8.W1 Station 2 Form Here]
Form ID: ________________
Station 3 – Design a Conservation Plan
25 Points | ~20 Minutes (Highest Value!)
COMPLETE THE STATION 3 FORM BELOW
Design your solution and justify your choices!
[EMBED G7.C8.W1 Station 3 Form Here]
Form ID: ________________
Missouri Ecosystem Connections: Trophic Cascades in Your Backyard
The Lost Apex Predators of Missouri
Missouri once had its own trophic cascade story—but unlike Yellowstone, we haven't brought the predators back. Gray wolves roamed Missouri forests and prairies until they were eradicated by the 1930s. Black bears were eliminated from most of the state by the 1950s (though they're slowly returning to Southern Missouri). Mountain lions were hunted to extinction by the early 1900s. The loss of these apex predators transformed Missouri ecosystems in ways we're still discovering.
Question to consider: If we removed wolves from Yellowstone and saw dramatic changes, what changed in Missouri when we removed OUR apex predators 50-100 years ago?
Missouri Trophic Cascade Case Study: Ozark National Scenic Riverways
The Ozark National Scenic Riverways in Southeast Missouri is one of the most biodiverse areas in the Midwest—protecting over 134 miles of pristine spring-fed rivers and diverse forest ecosystems. But without apex predators, we're seeing cascading effects:
| Trophic Level | Past (With Predators) | Present (Without Predators) | Cascade Effect |
|---|---|---|---|
| Apex Predators | Red wolves, black bears, mountain lions | Functionally extinct (occasional mountain lion sighting) | No top-down regulation |
| Mesopredators | Coyotes, bobcats, foxes (controlled by larger predators) | Mesopredator release—populations exploded | More nest predation, increased disease transmission |
| Herbivores | White-tailed deer (population ~15-20/sq mi) | Deer overabundance (~60-80/sq mi in some areas) | Forest understory overbrowsed |
| Vegetation | Diverse understory, forest regeneration | Reduced plant diversity, lack of tree regeneration | Degraded habitat quality |
| Birds/Insects | High songbird diversity, robust insect populations | Declining songbirds (habitat loss + mesopredator nest predation) | Reduced ecosystem services (pollination, pest control) |
The "Mesopredator Release" Phenomenon in Missouri
When apex predators disappear, medium-sized predators (mesopredators) explode in number—this is called mesopredator release. In Missouri:
- Coyote populations increased 200-300% statewide after wolf extirpation, moving into urban areas like St. Louis
- White-tailed deer populations reached unsustainable levels—no apex predators to control them, causing vehicle collisions and forest overbrowsing
- Raccoons and opossums thrive in urban St. Louis, raiding bird nests and spreading diseases like rabies and leptospirosis
- Feral hogs (invasive species) are expanding across Missouri, causing agricultural damage without apex predator control
St. Louis Urban Ecology: Trophic Cascades in Your City
Even in cities, trophic relationships matter. St. Louis's development removed apex predators and created novel urban ecosystems:
Forest Park & St. Louis's Urban Food Web
Top predators: Great blue herons, red-tailed
hawks, barred owls (replacing wolves/bears)
Mesopredators: Raccoons, opossums, domestic/feral
cats, foxes
Herbivores: Squirrels, rabbits, white-tailed deer
(in Forest Park and city parks)
Producers: Native trees (oaks, maples, sycamores)
+ invasive plants (bush honeysuckle, Bradford pear)
Key observation: Domestic cats kill an estimated
2.4 billion birds annually in the U.S.—acting as invasive
mesopredators in urban food webs. St. Louis's feral cat colonies
disrupt natural bird populations.
Mississippi & Missouri Rivers Confluence: An Aquatic Trophic Cascade
The Mississippi and Missouri Rivers confluence (near St. Louis) creates one of the most important freshwater ecosystems in North America and demonstrates aquatic trophic cascades:
| Factor | Impact on Food Web | Cascade Result |
|---|---|---|
| Overfishing of paddlefish | Fewer filter feeders → plankton imbalance | Plankton blooms → water quality decline → fish die-offs |
| Bald eagle recovery | DDT ban allowed eagles to return (apex fish predator) | Balanced fish populations → healthier river ecosystem |
| River otter reintroduction | Top predators regulate fish and crayfish populations | Maintain balance in river food web |
| Invasive Asian carp | No natural predators, outcompete native fish for food | Collapse of native fish populations → trophic cascade threatening commercial fisheries |
Critical Thinking Challenge: Should Missouri Restore Wolves?
Based on what you learned about Yellowstone, consider this debate:
Arguments FOR Restoration:
- Control deer overpopulation (vehicle collisions cost $150M/year in MO)
- Reduce mesopredator populations (coyotes, expanding feral hog problem)
- Restore forest health (reduce deer overbrowsing damaging Ozark ecosystems)
- Increase biodiversity (songbirds, small mammals, forest regeneration)
- Ecotourism revenue (Yellowstone earns $35M/year from wolves)
Arguments AGAINST Restoration:
- Rancher concerns (livestock predation costs)
- Human safety fears (unfounded—wolf attacks extremely rare)
- Habitat fragmentation (highways, cities limit territory)
- Political opposition (hunting lobby, farming/ranching industry)
- High cost ($50k-$100k per wolf reintroduction)
Real scientists debate this! The Missouri Department of Conservation has studied gray wolf habitat suitability in the Ozarks. Could the science change minds? What would YOU recommend, based on evidence?
Local Conservation Success: Black Bear Comeback
Missouri DOES have a successful apex predator restoration story! Black bears were nearly extinct by the 1950s (hunted and habitat loss). After decades of protection and habitat restoration, they're recovering:
- Population in 1960: ~50 bears in Missouri (only Southern Ozarks)
- Population today: ~800+ bears statewide and expanding northward
- Ecosystem impact: Bears are ecosystem engineers—dispersing seeds, controlling deer fawns and small mammals, and creating nutrient-rich sites. They're a keystone species!
- Where to see them: Mark Twain National Forest, Ozark National Scenic Riverways (Southern Missouri)
Lesson: Apex predator restoration CAN work in Missouri—we've done it before. The question is: will we do it again?
Exit Ticket – Ecosystem Dynamics Integration
23 Points | ~15 Minutes
COMPLETE THE EXIT TICKET BELOW
This is your final assessment for Week 1. Take your time!
[EMBED G7.C8.W1 Exit Ticket Form Here]
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Enrichment & Extension
Optional deep dives for early finishers.
Optional content if you finish early or want to go deeper.
Scientist Spotlight
Research a scientist who contributed to this week's topic area and describe their key findings.
Environmental Justice Connection
Explore how this week's science concepts connect to environmental justice issues in our community.