Ecology Population Growth and Regulation 2 — Questions and Answers
Question 1: Which equation correctly represents the net reproductive rate (R0) in a population?
- R0 = Σ(lx × mx) (Correct answer)
- R0 = birth rate / death rate
- R0 = N(t+1) / N(t)
- R0 = r × K
Correct answer: R0 = Σ(lx × mx)
R0 is calculated by summing the products of age-specific survivorship (lx) and fecundity (mx) across all age classes.
Question 2: A population grows from 500 to 550 individuals in one year. What is the per capita growth rate (r) approximately?
- 0.095 (Correct answer)
- 0.10
- 0.050
- 0.200
Correct answer: 0.095
r ≈ ln(550/500) = ln(1.1) ≈ 0.095 per year using the continuous growth formula.
Question 3: What does a survivorship curve Type II indicate about a population?
- Constant mortality rate at all ages (Correct answer)
- High juvenile mortality then stable adult survival
- Low early mortality with rapid decline in old age
- Mortality increases exponentially with age
Correct answer: Constant mortality rate at all ages
Type II survivorship curves are linear on a log scale, indicating a constant probability of dying at any age regardless of age class.
Question 4: Scramble competition occurs when limited resources are divided among all competitors such that:
- Everyone gets an insufficient share and many die (Correct answer)
- The strongest individuals get all resources
- Resources are evenly distributed ensuring survival
- Only dominant individuals reproduce
Correct answer: Everyone gets an insufficient share and many die
In scramble competition, resources are shared equally but often below the threshold needed for survival, leading to widespread mortality.
Question 5: Which demographic concept describes the time it takes a population to double in size under exponential growth?
- Doubling time (td = ln2 / r) (Correct answer)
- Generation time (T)
- Replacement rate (R0)
- Finite rate of increase (λ)
Correct answer: Doubling time (td = ln2 / r)
Doubling time is calculated as ln(2) divided by the intrinsic rate of increase (r), approximately 0.693/r.
Question 6: Allee effects are most likely to threaten population persistence when:
- Population density falls below a critical minimum threshold (Correct answer)
- Population density exceeds carrying capacity
- Birth rates exceed death rates
- Age structure is skewed toward juveniles
Correct answer: Population density falls below a critical minimum threshold
Allee effects cause reduced fitness at low densities due to factors like mate finding failure, making small populations vulnerable to extinction.
Question 7: In a stage-structured population model, a transition matrix element of 0.7 in row 2, column 1 represents:
- 70% probability of individuals moving from stage 1 to stage 2 (Correct answer)
- 70% survival of stage 2 individuals
- Fecundity of 0.7 offspring per stage 1 individual
- 70% mortality in stage 1
Correct answer: 70% probability of individuals moving from stage 1 to stage 2
In a Leslie or Lefkovitch matrix, off-diagonal elements below the diagonal represent the probability of transitioning from one stage to the next.
Ecology Population Growth and Regulation 2
Which equation correctly represents the net reproductive rate (R0) in a population?