Free Ecology Population Growth Models Questions and Answers 1 — Questions and Answers
Question 1: A population of yeast is introduced to a new, nutrient-rich environment in a laboratory setting. Initially, the population grows rapidly, doubling in size at regular intervals. Which of the following statements BEST describes this initial phase of growth?
- The population is experiencing logistic growth because it will eventually be limited by the container size.
- The population is exhibiting exponential growth, characterized by a constant per capita growth rate. (Correct answer)
- The growth rate is density-dependent, as the population size is increasing.
- The population has reached its carrying capacity (K) and will remain stable.
Correct answer: The population is exhibiting exponential growth, characterized by a constant per capita growth rate.
In an environment with abundant resources and no limiting factors, populations tend to exhibit exponential growth. This model is characterized by a J-shaped curve where the per capita growth rate (r) remains constant, and the total population growth accelerates as the number of individuals increases.
Question 2: Which of the following scenarios is an example of a density-independent limiting factor affecting a population?
- A viral disease spreads rapidly through a crowded colony of bats.
- Increased competition for nesting sites limits the reproductive success of seabirds on an island.
- A severe, late-spring frost kills a large percentage of oak tree seedlings in a forest. (Correct answer)
- A surge in the predator population causes a decline in the local rabbit population.
Correct answer: A severe, late-spring frost kills a large percentage of oak tree seedlings in a forest.
Density-independent factors affect a population regardless of its density. A frost is an abiotic, weather-related event that will impact the seedlings' survival whether there are many or few in the area. The other options (disease, competition, predation) are all density-dependent factors, as their effects become more pronounced as the population density increases.
Question 3: The logistic growth model is described by the equation dN/dt = rN((K-N)/K). What does the term (K-N)/K represent?
- The intrinsic rate of natural increase.
- The per capita death rate.
- The fraction of the carrying capacity that is still available for population growth. (Correct answer)
- The point at which the population growth rate is at its maximum.
Correct answer: The fraction of the carrying capacity that is still available for population growth.
In the logistic growth equation, 'K' is the carrying capacity and 'N' is the current population size. The term (K-N) represents how many more individuals the environment can support. Dividing this by K, (K-N)/K, gives the fraction of the carrying capacity that has not yet been utilized, which acts as a moderating force on the exponential growth term (rN).
Question 4: An organism that is long-lived, produces few, well-cared-for offspring, and lives in a stable environment is best described as:
- An r-strategist
- A K-strategist (Correct answer)
- Exhibiting exponential growth
- A pioneer species
Correct answer: A K-strategist
K-strategists are adapted to stable environments where the population tends to be near the carrying capacity (K). Their life history traits include long life, slow development, late reproduction, large body size, and significant parental investment in a few offspring. Elephants and humans are classic examples. In contrast, r-strategists thrive in unstable environments and produce many offspring with little parental care.
Question 5: A population of harbor seals experiences growth that initially is rapid, then slows, and finally fluctuates around a certain level. This pattern, which produces an S-shaped curve when plotted, is known as:
- Exponential growth
- Linear growth
- Demographic transition
- Logistic growth (Correct answer)
Correct answer: Logistic growth
The S-shaped (or sigmoidal) curve is the hallmark of the logistic growth model. This model describes how a population's growth rate decreases as it approaches the carrying capacity (K) of its environment due to limited resources. Initially, when the population is small and resources are plentiful, growth is nearly exponential, but it must slow down as environmental resistance increases.
Question 6: Which of the following is a key assumption of the basic logistic model of population growth?
- The carrying capacity (K) of the environment fluctuates randomly from year to year.
- The per capita rate of increase (r) grows as the population approaches K.
- All individuals in the population are equivalent, with the same birth and death rates regardless of age or size. (Correct answer)
- The population responds instantly to changes in resource availability.
Correct answer: All individuals in the population are equivalent, with the same birth and death rates regardless of age or size.
The basic logistic model simplifies reality by assuming that all individuals are identical and contribute equally to the population's growth rate. It does not account for age structure, genetic differences, or spatial distribution. It also assumes a constant carrying capacity and an immediate response to density, which are often not true in nature.
Free Ecology Population Growth Models Questions and Answers 1
A population of yeast is introduced to a new, nutrient-rich environment in a laboratory setting.
Initially, the population grows rapidly, doubling in size at regular intervals.
Which of the following statements BEST describes this initial phase of growth?