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AP Biology Practice Quiz: Effect of Density on Populations

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 9 questions to check your progress.

Question 1 of 9

What is the term for the maximum population size that an ecosystem's resources can sustainably support?

All Questions (9)

What is the term for the maximum population size that an ecosystem's resources can sustainably support?

A) Logistic growth limit

B) Population density

C) Carrying capacity (K)

D) Density-independent factor

Correct Answer: C

The provided content explicitly defines carrying capacity (K) as 'the maximum population size an ecosystem's resources can sustainably support.'

Based on the provided information, what is the direct relationship between the density of a population and the availability of resources for each individual?

A) As population density increases, resource availability per individual increases.

B) As population density increases, resource availability per individual decreases.

C) Population density and resource availability are unrelated.

D) Resource availability only affects populations with a low density.

Correct Answer: B

The content explains that the density of a population affects resource availability. A higher density means more individuals are competing for the same limited resources, thus decreasing the amount available per individual.

A contagious virus spreads rapidly through a highly concentrated flock of birds, but it spreads very slowly in a flock that is sparsely distributed. The effect of this virus is an example of a:

A) Density-independent factor

B) Density-dependent factor

C) Carrying capacity enhancer

D) Resource availability increase

Correct Answer: B

The virus's impact is more severe at a higher population density, which is the definition of a density-dependent factor. These factors impose limits on growth that are related to the size and concentration of the population.

As a population of fish in a small pond grows and approaches the pond's carrying capacity (K), which of the following is most likely to occur?

A) The population's growth rate will accelerate exponentially.

B) Density-independent factors will become the only limit on the population.

C) The population's growth rate will slow down as limiting factors increase.

D) The carrying capacity of the pond will increase to support more fish.

Correct Answer: C

The content states that density-dependent and density-independent factors lead to a logistic growth model as a population approaches its carrying capacity. A key feature of the logistic model is that the growth rate slows as the population nears K due to increased competition for resources and other limiting factors.

A wildfire burns through a large forest, killing a significant portion of a deer population regardless of how many deer were living per square mile. This event is best described as an effect of:

A) A density-dependent factor

B) A logistic growth pattern

C) The population exceeding its carrying capacity

D) A density-independent factor

Correct Answer: D

The wildfire's impact is not related to the density of the deer population; it affects the population regardless of its size or concentration. This is the definition of a density-independent factor.

Which of the following best explains how an environment's resource availability determines its carrying capacity (K)?

A) Carrying capacity is a fixed number and is not influenced by resource availability.

B) An abundance of resources allows a population to grow indefinitely, making K irrelevant.

C) The finite amount of sustainable resources imposes an upper limit on the number of individuals that can survive and reproduce.

D) Resource availability only influences density-independent factors, which do not determine K.

Correct Answer: C

Carrying capacity is fundamentally determined by the resources an ecosystem can sustainably provide. Limited resources for food, water, and shelter mean that only a certain maximum number of individuals can be supported long-term.

A population is growing in an environment and exhibiting a logistic growth pattern. What is the primary reason for the S-shaped curve of the logistic model?

A) The population's growth is consistently exponential without any limits.

B) Density-independent factors cause predictable fluctuations in population size.

C) As density increases, the negative effects of limiting factors slow the rate of growth.

D) The carrying capacity of the environment continuously increases with the population size.

Correct Answer: C

The logistic growth model shows that a population's growth rate decreases as it approaches the carrying capacity (K). This slowing is caused by the increasing impact of density-dependent limiting factors (like competition and disease) that become more pronounced at higher densities.

The key distinction between density-dependent and density-independent factors is that the influence of density-dependent factors:

A) is always related to weather or climate.

B) changes based on the population's size and distribution.

C) remains constant regardless of how large the population is.

D) only affects populations that are far below carrying capacity.

Correct Answer: B

The defining characteristic of density-dependent factors is that their effect on the population (e.g., mortality rate, birth rate) varies with population density. In contrast, density-independent factors have the same proportional effect on a population regardless of its density.

A long-term drought reduces the primary productivity (plant growth) in a grassland ecosystem. What is the most likely consequence for the carrying capacity (K) of a population of herbivores in this ecosystem?

A) K will increase because the herbivores will become more efficient at finding food.

B) K will remain the same, but the population will be regulated by density-independent factors.

C) K will decrease because the availability of a key resource has been sustainably reduced.

D) K will become irrelevant as the population switches to an exponential growth model.

Correct Answer: C

Carrying capacity (K) is determined by the sustainable availability of resources. Since the drought has reduced the amount of food (a key resource), the ecosystem can no longer support the same maximum number of herbivores. Therefore, the carrying capacity must decrease.