Ecology Population Growth Models 3 — Questions and Answers
Question 1: Which type of survivorship curve is characterized by high survival throughout life followed by rapid die-off in old age?
- Type I (Correct answer)
- Type II
- Type III
- Type IV
Correct answer: Type I
Type I survivorship curves (e.g., humans, elephants) show most individuals surviving to old age before experiencing a steep decline in numbers.
Question 2: A population modeled with discrete time steps uses the geometric growth equation N(t+1) = λN(t). When is this population declining?
- λ > 1
- λ = 1
- λ < 1 (Correct answer)
- λ = 0.5 only
Correct answer: λ < 1
When λ (the finite rate of increase) is less than 1, each time step produces fewer individuals, so the population shrinks toward extinction.
Question 3: Stochastic models of population growth are most important for predicting extinction risk in:
- Large stable populations near carrying capacity
- Very small populations where chance events matter greatly (Correct answer)
- Populations with very high intrinsic growth rates
- Populations in highly productive environments
Correct answer: Very small populations where chance events matter greatly
In small populations, random variation in birth, death, and environmental conditions can drive extinction even when deterministic models predict persistence.
Question 4: The net reproductive rate R₀ = 1 means a population is:
- Growing exponentially
- Declining toward extinction
- Exactly replacing itself each generation (Correct answer)
- At carrying capacity
Correct answer: Exactly replacing itself each generation
R₀ = 1 indicates each individual replaces itself exactly once per generation, meaning the population is stable (neither growing nor shrinking).
Question 5: Which of the following is a density-independent factor affecting population growth?
- Competition for food
- A sudden volcanic eruption (Correct answer)
- Predation pressure
- Disease transmission rate
Correct answer: A sudden volcanic eruption
Volcanic eruptions (and other natural disasters) affect populations regardless of their density, making them density-independent limiting factors.
Question 6: In the logistic model, negative feedback on growth becomes strongest when:
- N is much smaller than K
- N equals K/2
- N approaches K (Correct answer)
- r approaches zero
Correct answer: N approaches K
As N approaches K, the term (K-N)/K approaches zero, creating the strongest negative feedback and nearly stopping population growth.
Question 7: A population ecologist calculates r = 0.3/year for a species. This value represents:
- The number of offspring produced per individual per year
- The per capita rate of increase under current conditions (Correct answer)
- The carrying capacity divided by population size
- The probability of survival to reproductive age
Correct answer: The per capita rate of increase under current conditions
r, the intrinsic rate of natural increase, is the per capita rate of population change (births minus deaths per individual) under specific environmental conditions.
Ecology Population Growth Models 3
Which type of survivorship curve is characterized by high survival throughout life followed by rapid die-off in old age?