Invasive Species Dynamics

Anchoring Phenomenon

Imagine a healthy forest in North America where ash trees flourish, supporting native herbivores and carnivores. Suddenly, a new beetle, the Emerald Ash Borer, arrives from another continent. With no natural predators in this new environment, the beetle population explodes, and native ash trees start dying rapidly. How does this single invasive species alter the complex interactions within the ecosystem, and how can humans effectively intervene to restore stability without causing further harm?

Estimated Time

60 - 90 minutes

Materials

• Device with internet access
• Invasive Species Dynamics Simulation
• Student data table (below)

Instructions

1. Engage

• Read the anchoring phenomenon above.
• Brainstorm: Based on your knowledge of food webs, predict what might happen to the native herbivores (e.g., caterpillars) and carnivores (e.g., birds) if a significant number of native plants (e.g., ash trees) die off. Record your prediction in your notebook.

2. Explore

• Open the Invasive Species Dynamics Simulation.
• Observe the initial stable state of the ecosystem. The graph shows the populations of Native Flora, Native Herbivores, and Native Carnivores over time.
• Task 1: Establish a Baseline
  • Click Start. Let the simulation run until time ($t$) reaches approximately 100 units.
  • Pause the simulation.
  • Record the population sizes of Native Flora, Herbivores, and Carnivores in your data table under “Baseline”.
• Task 2: Introduce the Invasive Species
  • Reset the simulation and click Start. Wait a few seconds to ensure stability.
  • Click the Introduce Invasive Species button.
  • Let the simulation run until time ($t$) reaches 200. Observe the immediate and long-term effects on all populations.
  • Pause the simulation and record the population sizes in your data table under “Invasive Introduced (No Intervention)”.
• Task 3: Test Interventions
  • You have a $50K budget to mitigate the invasive species using three methods: Physical Removal, Pesticide Use, and Introduce Natural Predator.
  • Reset the simulation. Start it, and introduce the invasive species again.
  • Experiment with different combinations of interventions using the sliders. Note the costs and the side effects (e.g., pesticides harming native species).
  • Try to find the most effective strategy to restore the native populations while staying within budget.
  • Record your best intervention strategy and the resulting population sizes in your data table.

Data Collection Table

| Condition | Time ($t$) | Native Flora | Native Herbivore | Native Carnivore | Invasive Species | Observations / Evidence | | :— | :— | :— | :— | :— | :— | :— | | Baseline (Stable) | 100 | ___ | _____ | _____ | 0 | _____ | | Invasive Introduced (No Intervention) | 200 | _____ | _____ | _____ | _____ | _____ | | Best Intervention Strategy: _____ | 200+ | _____ | _____ | _____ | _____ | _______ |

3. Explain

• Based on your data, explain how the introduction of the invasive species affected the “complex interactions” in the ecosystem. Did it maintain its relatively consistent numbers and types of organisms, or did it become a “new ecosystem”?
• Describe the mechanism. Why did the invasive species have such a drastic effect? What was happening to the flow of energy and matter?

4. Elaborate

• Evaluate the different human interventions.
• Identify the strengths and weaknesses of each approach (Physical Removal, Pesticides, Natural Predator) based on the evidence from the simulation (consider costs, effectiveness, and unintended consequences).

5. Evaluate (Student Deliverable)

• Write an Argument: Construct a scientific argument answering the following question: To what extent can an ecosystem remain resilient when exposed to an invasive species, and what is the most effective way for humans to intervene?
• Your argument must:
  • Make a clear claim about ecosystem resilience and your recommended intervention.
  • Use specific quantitative evidence from your data table (population sizes under different conditions).
  • Use reasoning to connect your evidence to the concepts of complex interactions, resource availability, and ecosystem stability (HS-LS2-6).
• Record your argument in the Evidence Log within the simulation and summarize it here.

Teacher Notes & Alignment

• 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.
• SEPs: Engaging in Argument from Evidence. Students evaluate the claims regarding ecosystem stability and intervention effectiveness, using evidence generated from the simulation.
• DCIs: LS2.C: Ecosystem Dynamics, Functioning, and Resilience. Students observe how extreme fluctuations in conditions (invasive species) challenge the functioning of ecosystems.
• CCCs: Stability and Change. Students observe a stable ecosystem, disrupt it, and attempt to restore stability.

Evidence Statements Addressed:

• Students evaluate the claims about complex interactions maintaining stable ecosystems vs. changing conditions resulting in new ecosystems.
• Students identify and describe additional evidence regarding changes in the numbers of species and organisms subject to an extreme change (invasive species introduction).
• Students evaluate the reasoning regarding how extreme fluctuations in population size challenge the functioning of ecosystems in terms of resources.