Week 4: Food Web Complexity & Stability
Grade 8 Science | Rosche | Kairos Academies
Simulation: Food Web Stability
PREDICT
You can build food webs with 5, 10, or 15 species. Predict: Which food web (simple or complex) will be more stable when you remove a species? Why?
OBSERVE
Try all 3 complexity levels. Remove the same type of species (e.g., a top predator) from each. Record: (1) How many other species are affected? (2) Does the stability meter drop equally? (3) Which web recovers and which collapses?
EXPLAIN
Why do complex food webs resist species loss better than simple ones? Use the terms "redundancy," "energy pathways," and "keystone species" in your explanation.
YOUR TURN - Full Ecosystem Analysis (Week 4 Mastery):
- Identify the trophic cascade: Trace the chain reaction from otter loss to urchin explosion to kelp loss to fish decline.
- Calculate energy flow impact: Apply the 10% rule from Week 1. If kelp biomass drops by 95%, how much energy is available to herbivores? To predators?
- Analyze food web connections: This ecosystem had low redundancyโonly ONE major kelp predator (urchins) controlled by ONE major predator (otters). How did this single-connection vulnerability cause collapse?
- Integrate decomposition (W3): What happens to nutrient cycling when 95% of kelp biomass disappears?
- Compare to invasive species (W2): Is this cascade similar to an invasive species effect? What's different about removing a native keystone species vs. adding an invasive one?
- Design a restoration plan: Should scientists reintroduce otters immediately? Or rebuild kelp first? Justify using food web complexity principles.
Challenge: If this ecosystem had 3 different urchin predators instead of just otters, would the cascade have been as severe? Explain using the "Insurance Hypothesis"!
Fading Support Progress: Week 1 showed all steps. Week 2-3 had partial support. This week, YOU complete the full analysis independently! This builds your problem-solving stamina for the upcoming cycle assessment.
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Detailed walkthrough when you need more guidance.
Trace the cascade:
- Wolves removed > Elk have NO predators
- Elk population INCREASES > Elk eat MORE plants
- Plants near rivers are eaten > Trees/willows DISAPPEAR
- No trees > Beavers can't build dams > Beavers LEAVE
- No beaver dams > Water flows faster > EROSION increases
- No trees > Songbirds have nowhere to nest > Songbirds DECLINE
That's a TOP-DOWN cascade! One change at the TOP rippled down through EVERYTHING.
Complete Your Worksheet โ Click to Expand
Complete the "Station 2" box in the "STATION 1 & 2 NOTES" section:
- Keystone species affect ecosystems by... (mechanism)
- The Yellowstone cascade shows... (what happened)
- Key insight: (one sentence summary)
Complete Your Worksheet โ Click to Expand
Complete the "STATION 3 NOTES" section on your worksheet:
- My restoration path is... (which approach did you choose?)
- This works because... (mechanism using food web science)
- A potential unintended consequence... (what could go wrong?)
- Key insight: (one sentence summary)
Complete Your Worksheet โ Click to Expand
Complete the "DAY 2 EXIT TICKET" and "SCIENCE CIRCLE" sections:
- Q1 (NEW): How food web complexity affects resilience
- Q2 (SPIRAL): Apply Week 1-3 concepts to ecosystem stability
- Q3 (INTEGRATION): Connect all 4 weeks to explain ecosystem survival
- Science Circle: Your "Aha!" moment and remaining question
Bonus: +5 points for Day 2 Exit Ticket, +3 points for Science Circle!
Enrichment & Extension
Optional content if you finish early or want to go deeper.
Systems Thinking: Feedback Loops in Ecosystems
Complex food webs exhibit negative feedback loops that stabilize populations. When one species grows too abundant, predators increase, bringing it back down. Simple food webs lack these stabilizing mechanisms. This connects to climate systems (Cycle 5) and plate tectonics (Cycle 6)โcomplexity creates resilience across all Earth systems, not just ecosystems!
Scientist Spotlight: Dr. Ayana Elizabeth Johnson
Dr. Ayana Elizabeth Johnson is a marine biologist, policy expert, and conservation strategist who studies how to protect ocean ecosystems while supporting coastal communities. She co-founded the Urban Ocean Lab, a think tank focused on coastal cities and climate change. Her research on Caribbean coral reefs showed that when coastal communities have a voice in conservation decisions, marine protected areas are more effective. Dr. Johnson's work bridges the gap between science and justice, asking not just "How do we save coral reefs?" but "Who gets to decide, and who benefits from conservation?"
Environmental Justice: Mississippi River Food Web Degradation
The Mississippi River's complex food web supports over 150 fish species and provides billions of dollars annually through fishing and tourism. But industrial pollution and agricultural runoff create environmental justice issues. Low-income communities and communities of color near St. Louis experience higher pollution exposure while working in industries that degrade the river ecosystem. When industrial facilities release pollutants, fish kills cascade through food webs, devastating commercial and subsistence fishersโmany of whom are working-class families who have fished these waters for generations. Ecosystem resilience requires both biological diversity AND social justiceโprotecting the web of life means protecting the people connected to it.
Week 4 Complete!
Next Week: Cycle 4 Synthesis & Assessment โ Bringing together energy flow, invasive species, decomposition, and ecosystem stability!