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AP Environmental Science Unit 3 Visual Review

A 9-slide visual walkthrough of every Topic 3.1-3.9 concept — generalist/specialist and r/K-selected species, survivorship curves, carrying capacity, population growth models, age structure, and the demographic transition — built right into the page.

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TOPIC 3.1 Generalist & Specialist Species Generalist raccoon, rat, crow Specialist koala, panda ← wide niche, broad diet, tolerant of change narrow niche, specific needs → Generalists Can survive on many food sources, in many habitats, across a wide range of conditions. They adapt well to human-disturbed landscapes and are rarely at risk of extinction. Broad niche = a wide range of tolerance (2.4). Specialists Depend on a narrow range of food, habitat, or conditions — a koala needs eucalyptus leaves specifically. Efficient in a stable niche, but highly vulnerable when that niche disappears. The tradeoff: specialists outcompete generalists in a stable niche, but can't adapt when it changes. The Review Hub · AP Environmental Science Unit 3 TOPIC 3.2 K-Selected & r-Selected Species r-selected many offspring, little parental care • Short lifespan, early reproduction • Thrive in unstable, unpredictable environments • Population near exponential growth • Examples: insects, mice, dandelions "r" = the growth-rate variable in the exponential model — r-selected species maximize it. K-selected few offspring, high parental care • Long lifespan, delayed reproduction • Thrive in stable, predictable environments • Population stays near carrying capacity • Examples: elephants, whales, humans "K" = carrying capacity (3.4) — K-selected species are adapted to live steadily near it. Neither strategy is inherently better — each is the winning bet for a different kind of environment. The Review Hub · AP Environmental Science Unit 3 TOPIC 3.3 Survivorship Curves survivors (log scale) % of maximum lifespan → Type I Type II Type III Type I — late loss Low mortality when young, most individuals survive to old age, then die off sharply. K-selected species: humans, elephants. High parental investment protects the young. Type II — constant risk Roughly equal mortality risk at every age. Example: many birds, squirrels. Type III — early loss Massive early mortality; the few survivors live long. r-selected: fish, insects, plants. The curve's shape is a direct fingerprint of the species' reproductive strategy from Topic 3.2. The Review Hub · AP Environmental Science Unit 3 TOPIC 3.4 Carrying Capacity population size time → carrying capacity (K) growth oscillation around K Definition Carrying capacity (K) is the maximum population size an environment can sustain INDEFINITELY, set by limiting resources — food, water, space, or shelter. Overshoot & die-off Populations rarely sit exactly at K. They often overshoot it (there's a lag before resource depletion is felt), then experience a die-off back toward or below K — producing the oscillation pattern seen in the graph. K isn't fixed — it shifts if resource availability changes, which is exactly Topic 3.5's subject. The Review Hub · AP Environmental Science Unit 3 TOPIC 3.5 Exponential vs. Logistic Growth population size time → exponential (J) K logistic (S) Exponential growth Occurs when resources are UNLIMITED — growth rate is proportional to population size, so the curve accelerates forever ("J-shaped"). Rare in nature — seen briefly after colonizing a new habitat. Logistic growth Occurs when resources are LIMITED. Growth starts fast, then slows as the population nears carrying capacity (K), leveling into an "S-shaped" curve. This is the realistic model for most natural populations. Same starting shape, different ending — the presence of a resource limit is what bends the J into an S. The Review Hub · AP Environmental Science Unit 3 TOPIC 3.6 Age Structure Diagrams Expansive wide base — growing fast Stable even sides — steady size Contractive narrow base — shrinking Each bar = an age group's population; longer bars near the bottom (young) predict future growth. Read the base: wide = growing, even = stable, narrow = shrinking. The shape IS the forecast. The Review Hub · AP Environmental Science Unit 3 TOPIC 3.7 Total Fertility Rate 1.3 South Korea 1.7 United States replacement level ≈ 2.1 2.1 World average 4.6 Niger What TFR means Average children per woman over her lifetime. Below 2.1, a population shrinks without immigration. The ~2.1 replacement figure is slightly above 2.0 to offset children who don't survive to reproduce. The Review Hub · AP Environmental Science Unit 3 TOPIC 3.8 Human Population Dynamics Growth rate = (births − deaths) ÷ population × 100 Birth rate ↓ when: • Women gain education • Access to contraception • More women in workforce • Cities replace farms (fewer child-workers) • Delayed marriage age Death rate ↓ when: • Better healthcare access • Clean water & sanitation • Vaccines & modern medicine • More reliable food supply • Lower infant mortality Why the gap between them matters Death rates fall FIRST as a country develops (healthcare arrives quickly), while birth rates fall more slowly (cultural change takes time). That LAG between the two curves is exactly what produces rapid population growth — and it's the engine behind Topic 3.9's model. Every factor here is really a birth-rate or death-rate lever — memorize which side each one pushes. The Review Hub · AP Environmental Science Unit 3 TOPIC 3.9 The Demographic Transition Model STAGE 1 STAGE 2 STAGE 3 STAGE 4 birth rate death rate population 1: high birth & death, stable · 2: death falls first, population booms · 3: birth falls, growth slows 4: both low, stable population — some models add a Stage 5 where birth falls below death. The widening gap in Stage 2 is where almost all of the last 200 years of world population growth happened. The Review Hub · AP Environmental Science Unit 3
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How to use the visual review

Spend 30 seconds per slide before clicking next. Look at the diagram, then ask yourself: "Could I draw this from memory and explain it?"

Use the fullscreen button () on desktop for the best experience. Use arrow keys to navigate. Tap "Show all slides" to jump around.

This covers every one of Unit 3's 9 CED topics, from species survival strategies through the demographic transition model.