Invasive Species Case Study: Zebra Mussels
Population growth modeling, using a real Great Lakes invasive species.
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Standards
HS-LS2-2 — Use mathematical representations to support and revise explanations based on evidence about factors affecting biodiversity and populations in ecosystems.
Why Does This Matter?
Zebra mussels arrived in the Great Lakes in the late 1980s via ship ballast water and spread through the Detroit River into every one of the Great Lakes within a few years — one of the most studied invasive species events in the region's history.
Objective
Research how zebra mussels altered Great Lakes food webs, then model and graph the population growth curve of a species with few natural predators.
Materials
- Provided background reading on zebra mussel introduction and impact (teacher-provided or researched)
- Graph paper or graphing software
- Calculator
Note: This is a research and modeling lab — no physical safety hazards.
Procedure
- Research (or read the provided background) on how and when zebra mussels entered the Great Lakes, and list at least three ecosystem effects they caused (e.g. filtering water clarity, outcompeting native mussels, clogging water intake pipes).
- Using a provided starting population and growth rate (teacher-provided, based on real early-invasion estimates), calculate the population size for 6 generations assuming unlimited resources and no predators (exponential growth: each generation's population = previous population × growth rate).
- Graph population size (y-axis) vs. generation number (x-axis).
- Research one method used to manage or slow zebra mussel spread (e.g. ballast water regulations, boat inspection), and summarize how it targets the invasion pathway.
Data Table
| Generation | Population size | Change from previous generation |
|---|---|---|
| 0 (starting) | — | |
| 1 | ||
| 2 | ||
| 3 | ||
| 4 | ||
| 5 | ||
| 6 |
Analysis Questions
- What shape does your population graph make? What does that shape tell you about unchecked population growth?
- Why do invasive species like zebra mussels often grow faster in a new ecosystem than in their native one?
- List two ways zebra mussels changed the Great Lakes food web, and explain whether each effect was positive or negative for native species.
- Real zebra mussel populations don't grow exponentially forever. What factors do you think eventually limit their population (even without a strong predator)?