Ecosystem Resilience and Disturbances

Estimated Time: 45-60 minutes

Materials: Device with internet access, Ecosystem Resilience and Disturbances Simulation, notebook/data table

Part 1: Engage (Anchoring Phenomenon)

In 1988, massive fires swept through Yellowstone National Park, burning over a third of the park. Many predicted that the ecosystem was permanently destroyed. However, within a few years, new plant growth had surged, and animal populations stabilized. Yet, in other areas of the world, a single severe drought or pollution event can turn a thriving forest into a barren wasteland that never recovers.

Question: Why do some ecosystems recover from major disasters while others change permanently?

1. What factors do you think determine whether an ecosystem can “bounce back” from a disturbance?
2. Write down one question you have about how species interact to maintain stability in an ecosystem.

Part 2: Explore (Simulation Investigation)

Use the Ecosystem Resilience and Disturbances Simulation to investigate population dynamics. The simulation models a simplified ecosystem containing Plants, Herbivores, and Carnivores.

1. Baseline Stability
   • Click Start. Let the simulation run until Time = 100 years.
   • Observe the population numbers on the left and the graph on the right.
   • Data Collection: Record the approximate stabilized populations.
     • Plants: _____
     • Herbivores: _____
     • Carnivores: _____
2. Modest Disturbance
   • At Time = 100, click the Apply Modest Disturbance button. This simulates a temporary drought that lowers the carrying capacity ($K$) of the plants.
   • Observe the populations during the disturbance and for 50 years after it ends.
   • Data Collection: Did the populations return to their original baseline numbers? (Yes/No)
3. Extreme Disturbance
   • Click Reset, then Start. Let the baseline stabilize (Time = 50).
   • Click the Apply Extreme Disturbance button. This simulates a severe event that wipes out large portions of populations and permanently degrades the carrying capacity ($K$).
   • Observe the populations for 100 years after the disturbance.
   • Data Collection: Record the new stabilized populations (or note if any species go extinct).
     • Plants: _____
     • Herbivores: _____
     • Carnivores: _____

Part 3: Explain (Sensemaking)

Using the data you collected from the simulation, answer the following questions:

1. Look at the baseline stability. Even when there was no disturbance, did the populations stay at exactly the same number constantly, or did they fluctuate slightly? Explain why this happens based on the interactions between plants, herbivores, and carnivores.
2. When the Modest Disturbance was applied, what happened to the populations? How long did it take for them to recover to their original status?
3. When the Extreme Disturbance was applied, how did the ecosystem change? Did it return to its original status, or did it form a new ecosystem state? Use evidence (population numbers) to support your answer.

Part 4: Elaborate/Evaluate (Argumentation)

A local politician argues: “We don’t need to worry about protecting local habitats from development because nature is resilient. Ecosystems always adapt and bounce back from whatever happens to them.”

Your Task: Evaluate this claim. Write an argument assessing the strengths and weaknesses of the politician’s claim. Your argument must include:

• Claim: Does the evidence support or refute the politician’s statement?
• Evidence: Cite specific population data from your simulation regarding modest AND extreme disturbances.
• Reasoning: Explain why a complex set of interactions allows an ecosystem to remain stable or recover from a modest disturbance, but why extreme fluctuations in habitat availability (carrying capacity) can result in a completely new ecosystem.

Extension Options:

• Mathematical Modeling: Have students graph the Lotka-Volterra equations alongside the simulation data to predict carrying capacity changes.
• Climate Change Connection: Discuss how global temperature rise might act as a continuous ‘modest disturbance’ and debate whether this will eventually force an ‘extreme’ ecosystem shift.

Teacher Notes & Alignment

This task is aligned with HS-LS2-6: Evaluate the claims, evidence, and reasoning that the complex interactions in ecosystems maintain relatively consistent numbers and types of organisms in stable conditions, but changing conditions may result in a new ecosystem.

Three-Dimensional Learning:

• SEP: Engaging in Argument from Evidence – Students evaluate a specific claim about ecosystem resilience and use simulation data to defend or critique the claim.
• DCI: LS2.C: Ecosystem Dynamics, Functioning, and Resilience – Students observe that ecosystems maintain consistent numbers over long periods under stable conditions, that they can return to original status after a modest disturbance, and that extreme fluctuations can cause a new ecosystem state.
• CCC: Stability and Change – Students construct explanations for how the ecosystem remains stable and how it changes in response to different scales of disturbance.

Evidence Statements Addressed:

• 1.a & 1.b: Students identify the explanation being evaluated (the politician’s claim) and evaluate it based on evidence from the simulation regarding ecosystem stability and new ecosystem formation.
• 3.a: Students describe the strengths and weaknesses of the claim based on the relationship between species and the carrying capacity (physical environment) in the ecosystem.
• 3.b & 3.c: Students use evidence to support the argument that the resiliency of an ecosystem is subject to the degree of change (modest vs. extreme), and they assess the logic of the reasoning regarding how extreme fluctuations challenge ecosystem functioning.