The Lyme Disease Balancing Act: Ticks, Deer, and Biodiversity

Part 1: Engage (Anchoring Phenomenon)

In the suburban forests of the Northeast, a walk through the woods feels peaceful. However, beneath the leaves, a complex biological “cascade” is unfolding. In some years, a single hiker might find dozens of ticks on their clothes, while in other years, they find none. This isn’t random—it’s driven by the volume of acorns dropping from oak trees.

Initial Reflections:

  1. How could a tree dropping seeds (acorns) possibly lead to a human being getting a bacterial infection?
  2. What are three animals you think play a role in the “Lyme disease ecosystem”?
  3. Generate a “need to know” question about the timing of disease outbreaks.

Part 2: Explore (Simulation Investigation)

Open the Lyme Disease Ecological Cascade Simulation and observe the population dynamics.

The Acorn-Mouse Connection

Wait for the simulation to stabilize (Year 5). Then, click “Trigger Oak Mast Year.” Closely watch the chart and record when each population reaches its peak.

Event Year of Peak Observation (What happened to the line?)
Oak Mast Triggered    
Mice Population Peak    
Infected Tick Nymph Peak    
Human Lyme Risk Peak    

Predator and Climate Variables

Reset your focus. Observe how these two independent variables impact the “baseline” (the normal level) of Lyme risk.

  1. Predator Pressure: Move the Fox Population slider to High. Wait 5 years. What happens to the Mouse baseline and the Nymph baseline?
  2. Climate Stress: Move Winter Severity to High. How does this affect the survival of ticks compared to mice?

Part 3: Explain (Trophic Cascades)

  1. The Delayed Response: Why did the Human Lyme Risk not peak in the same year as the acorns? Use the biological life cycle of a tick (larva to nymph) to explain this multi-year lag.
  2. Mathematical Analysis: Based on your observations, which variable—Foxes or Deer—has a more direct impact on the number of infected nymphs? Explain your reasoning using data from the sliders.
  3. Biodiversity and “Dilution”: If a forest has a high fox population and a diverse community of small mammals (not just mice), why might the risk of Lyme disease for humans be lower?

Part 4: Elaborate/Evaluate (Management Strategies)

Public Health Advisory

You have been hired by a State Park to manage the forest to reduce human Lyme disease risk. You have three potential management plans:

Plan A: Deer Culling (Reduce Deer Density to Low) Plan B: Predator Protection (Maximize Fox Population) Plan C: Habitat Restoration (Plant diverse trees to reduce the impact of Oak Mast events)

The Challenge:

  1. Using the simulation, test Plan A and Plan B.
  2. Which plan resulted in a lower average Human Lyme Risk over a 10-year period?
  3. Final Evaluation: Write a short recommendation to the State Park director. Support your recommendation with evidence from the simulation’s mathematical representations (the charts). Use the terms carrying capacity, trophic level, and population fluctuation.