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Volume I · MMXXVI AP Environmental Science
Library› AP Environmental Science› Unit 3: Populations
⁂   AP Environmental Science · Unit 3

3. Populations

10–15% of the AP exam. 13 key topics. 4 common errors analyzed.

10–15% exam weight

Unit 3: Populations

Unit 3 (Populations) addresses environmental systems and human impacts. FRQs in this unit typically ask you to identify problems, propose specific solutions, and explain environmental consequences.

Key topics in this unit

  1. Generalist vs. specialist species
  2. K-selected vs. r-selected species
  3. Survivorship curves: Type I, Type II, and Type III
  4. Carrying capacity (K) and limiting factors
  5. Exponential population growth model
  6. Logistic population growth model
  7. Density-dependent and density-independent limiting factors
  8. Age structure diagrams and their interpretation
  9. Total fertility rate (TFR) and replacement fertility
  10. Human population demographics
  11. Demographic transition model (stages 1–4)
  12. Rule of 70 and doubling time calculations
  13. Population growth rate calculations

Common errors — what the rubric penalizes

These are the most frequently penalized mistakes on AP exam FRQs and MCQs. Review each before your next practice session.

Common error

Confusing density-dependent limiting factors (competition, predation, disease — intensify as population grows) with density-independent factors (natural disasters, climate events — act regardless of population size)

Common error

Misreading age structure diagrams: students often focus only on the overall shape without correctly identifying whether the base (younger cohorts) is expanding, stable, or contracting to project future growth

Common error

Applying the Rule of 70 incorrectly by using a decimal growth rate (e.g., 0.02) instead of the percentage value (2), yielding a doubling time 100× too large

Common error

Conflating logistic and exponential growth curves when describing real-world populations — real populations approach carrying capacity (S-curve), not unbounded exponential growth

Study checklist

  • Can you list all key topics from memory without this page?
  • Have you worked through at least one FRQ-style question per topic?
  • Can you explain each common error above — and why the correct answer differs?
  • Have you reviewed the relevant College Board CED section and formula sheet entries?
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