AP Environmental Science Unit 3: Populations | Notes and practice

Notes

Generalists have broad niches and adapt well to change (raccoons). Specialists have narrow niches and are more vulnerable (pandas).
K-selected species: few offspring, lots of parental care, long lives, populations near carrying capacity (elephants, whales). They recover slowly from disturbance.
r-selected species: many offspring, little care, short lives (insects, mice). They're often invasive and recover quickly.
Survivorship curves: Type I (most survive to old age, like humans), Type II (constant death rate, like many birds), Type III (most die young, like fish and oysters).

Type I: most survive to old age. Type II: steady losses. Type III: most die young.

Carrying capacity ($K$): the largest population the environment can support. Overshooting $K$ leads to a die-off.
Exponential growth (J-curve) happens with unlimited resources; logistic growth (S-curve) levels off at $K$.
Density-dependent limits (food, disease) and density-independent limits (natural disasters).

A population overshooting K can crash; logistic growth levels off.

Growth rate (%) $\displaystyle = \frac{\text{birth rate} - \text{death rate}}{10}$ when rates are per 1,000 people.
Rule of 70: doubling time (years) $\displaystyle \approx \frac{70}{\text{growth rate in \%}}$.
Total fertility rate (TFR): average children per woman. Replacement level is about 2.1.
Age-structure diagrams: a wide base means rapid growth; a column shape means stable; a narrow base means decline.
Demographic transition model: pre-industrial (high birth and death rates), transitional (death rate falls first, so growth is rapid), industrial (birth rate falls), post-industrial (both low).
Factors that lower TFR: education and jobs for women, access to family planning, higher income, and lower infant mortality.

Death rates fall first (Stage 2), then birth rates fall (Stage 3).

Which trait describes a K-selected species?

Oysters release millions of eggs, and most die young. Their survivorship curve is:

A country has a birth rate of 30 and a death rate of 10 per 1,000. What is its growth rate?

Using the rule of 70, how long will it take that country's population to double?

An age-structure diagram with a very wide base suggests:

In the transitional stage of the demographic transition model:

Which factor most often lowers a country's total fertility rate?

A deer population overshoots its carrying capacity. What usually follows?

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Free-response question

A country has a birth rate of 24 per 1,000, a death rate of 8 per 1,000 and a TFR of 3.2.

(a) Calculate the growth rate and doubling time.

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Growth rate $\displaystyle = \frac{24 - 8}{10} = 1.6\%$. Doubling time $\displaystyle \approx \frac{70}{1.6} \approx 44$ years.

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(b) Identify the stage of the demographic transition model the country is most likely in. Justify.

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Transitional (stage 2 moving to 3): the death rate is low but the birth rate is still fairly high, so the population grows quickly.

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(c) Describe one policy that could lower the TFR.

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Increasing access to education for girls and women, or making family planning widely available.

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