PRACTICE

🧩 Multiple Choice Answer Key + Explanations

1. Which of the following best describes a generalist species?
âś… Answer: B. Broad niche, can live in many environments
Explanation:
Generalist species can tolerate a wide range of environmental conditions and use a variety of resources (e.g., raccoons, humans). They’re adaptable to change — unlike specialists, which need very specific conditions.

2. Which species is most likely to have a Type III survivorship curve?
âś… Answer: C. Sea turtles
Explanation:
Type III curves show high early mortality but high survival for the few that reach adulthood — common in r-selected species like sea turtles, insects, and fish.

3. If a country’s population growth rate is 1.4%, its doubling time is approximately:
âś… Answer: 50 years
Explanation:
Using the Rule of 70:

70Ă·1.4=5070 Ă· 1.4 = 5070Ă·1.4=50

So the population would double in roughly 50 years.

4. In the demographic transition model, when do birth rates begin to fall?
âś… Answer: C. Stage 3 (Industrial)
Explanation:
In Stage 3, economic development, urbanization, and access to education and contraception cause birth rates to decline, reducing population growth.

5. A K-selected species would most likely:
âś… Answer: D. Maintain population near carrying capacity
Explanation:
K-selected species have few offspring, provide parental care, and have populations that fluctuate around the environment’s carrying capacity (K). Examples include elephants and humans.

✏ Short Answer Explanations

1. Explain how resource availability limits population growth.

  • Populations grow exponentially when resources (food, water, space) are abundant.

  • As resources become scarce, competition increases, slowing growth until the population stabilizes at the carrying capacity (K).

  • If a population exceeds K, overshoot occurs, often followed by dieback (population decline).

2. Describe how an age structure diagram can predict future population trends.

  • A wide base (many young people) predicts rapid growth.

  • A rectangular shape (similar numbers across age groups) predicts stable growth.

  • An inverted shape (fewer young people) predicts population decline.
    These shapes reflect the country’s birth rate, death rate, and development level.

3. Compare and contrast r-selected and K-selected species.

Trait

r-Selected

K-Selected

Offspring number

Many

Few

Parental care

Little to none

High

Lifespan

Short

Long

Reproductive age

Early

Late

Example

Mice, insects

Elephants, humans

Summary:
r-selected species thrive in unstable environments, while K-selected species thrive in stable, competitive ones.

4. Why does total fertility rate typically decrease as a nation becomes more developed?

  • Higher education and workforce participation for women

  • Access to contraception and family planning

  • Urbanization (less need for large families)

  • Increased child survival (less incentive for more births)
    → As development rises, birth rates and TFR decline.

5. How can a population overshoot its carrying capacity, and what happens afterward?

  • Overshoot occurs when population temporarily exceeds the environment’s resource limit due to high reproduction or resource abundance.

  • After overshoot, resource depletion causes dieback (sharp population decline).

  • Example: Deer population explosion followed by starvation when food runs out.