AP Biology Unit 8 Review – Ecology (2025 Exam Prep)

AP Tip: Be ready to interpret energy pyramids—only ~10% of energy transfers between trophic levels.

2. Population Ecology

Key Concepts:

• Population size (N)
• Density and distribution patterns: Clumped, uniform, random
• Growth models:
  • Exponential (J-shaped) – unlimited resources
  • Logistic (S-shaped) – limited resources, carrying capacity (K)

Population Regulation:

• Density-dependent factors: Competition, predation, disease
• Density-independent factors: Natural disasters, climate

3. Community Interactions

• Competition: Species compete for the same resources
• Predation: Predator-prey relationships shape populations
• Mutualism: Both species benefit (e.g., pollinators and plants)
• Commensalism: One benefits, other unaffected
• Parasitism: One benefits at expense of other

4. Nutrient Cycles

Water Cycle: Evaporation → Condensation → Precipitation → Runoff
Carbon Cycle: Photosynthesis, respiration, combustion
Nitrogen Cycle: Nitrogen fixation, nitrification, denitrification
Phosphorus Cycle: Rock weathering, absorption by plants

5. Human Impacts

• Climate change from greenhouse gases
• Habitat destruction and fragmentation
• Invasive species disrupting ecosystems
• Pollution (air, water, soil)
• Overexploitation of resources

Conservation Biology Strategies:

• Habitat restoration
• Captive breeding programs
• Protected areas and biodiversity hotspots

6. Connections to Other Units

• Unit 3: Energy flow connects to cellular energetics
• Unit 7: Natural selection pressures in ecosystems
• Unit 5 & 6: Genetic diversity affects population resilience

Common AP Biology Exam Questions for Unit 8

Multiple Choice Examples:

• Calculate carrying capacity from a logistic growth graph
• Predict effects of removing a top predator on ecosystem stability

FRQ Examples:

• Analyze the impact of an invasive species on nutrient cycling
• Design an experiment to test the effect of temperature on plant growth rates

Study Tips for Unit 8

1. Know the Cycles: Draw and label each nutrient cycle.
2. Practice Graph Analysis: Especially logistic vs. exponential growth curves.
3. Learn Interaction Examples: Be able to match examples to interaction types.
4. Review Human Impact Case Studies: Coral bleaching, deforestation, climate change.

Frequently Asked Questions

1. How much of the AP Bio exam is Unit 8?
About 8–11% of the test.

2. Do I need to memorize every species interaction example?
No—know definitions and at least one clear example for each type.

3. Are math calculations in ecology common?
Yes—be ready for growth rate and energy transfer percentage problems.

4. What’s the most challenging part of Unit 8?
Interpreting multi-variable ecosystem data in FRQs.

Call to Action

Unit 8 closes out AP Biology with big-picture thinking—how life interacts at every scale. Master it, and you’ll be ready for synthesis questions that pull from multiple units.

Use RevisionDojo’s ecology practice sets and data interpretation FRQs to secure every last point on test day.