AP Environmental Science Unit 3 Cheatsheet: Populations

Start with the first 3 sections of the Unit 3 one-page cheatsheet below. The full sheet is a PDF you can print.

Generalist vs. Specialist Species

Generalist	Specialist
Thrive in changing habitats	Thrive in constant habitats
Flexible diet & habitat use	Narrow niche requirements
Better at colonizing new areas	Vulnerable to habitat change

Key distinction: Environmental stability determines which strategy succeeds.

Survivorship Curves

Definition: Line showing relative survival rates of a cohort (same-age group) from birth to maximum age.

Type	Pattern	Species
Type I	High survival until old age, then steep drop	K-selected (humans, elephants)
Type II	Constant mortality rate across ages	K-selected (some birds)
Type III	High early mortality, then plateau	r-selected (fish, insects)

Reading curves: Steep slope = high mortality in that age range; flat slope = low mortality.

Human Population Dynamics & Demographic Metrics

Population change equation:

Growth = Birth rate − Death rate + Immigration − Emigration

Rate of Natural Increase (RNI):

RNI (%) = (Crude birth rate − Crude death rate) ÷ 10

Population doubling time: 70 ÷ annual growth rate (%) = years to double

Factors affecting birth & death rates: Education, family planning, healthcare, nutrition access.

Malthusian limits: Earth's carrying capacity constrains human population growth.

The rest of the Unit 3 sheet

7 more sections are on the one-page PDF:

K-Selected vs. r-Selected Species
Age Structure & Population Growth
Total Fertility Rate (TFR) & Human Population
Invasive Species & Selection Strategy
Carrying Capacity (K) & Overshoot
Resource Availability & Population Growth
Demographic Transition Model (DTM)

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Unit 3: Populations on one page, aligned to the 2026-2027 course. Made and checked by the Fiveable Content Team.

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