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AP®BiologyCollege BoardExam QuestionsUnit 8: EcologyPopulation & Community Ecology

Population & Community Ecology (College Board AP® Biology): Exam Questions

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Population & Community Ecology

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1
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A deer population in a national park initially grows rapidly, but then stabilizes at around 1500 individuals due to limited food resources.

Which of the following describes the maximum number of individuals that an environment can support?

  • Transition phase

  • Exponential limit

  • Trophic level threshold

  • Carrying capacity

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2
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Ecologists measured species diversity in two forests using Simpson’s index of diversity (D). They found that forest A had a D value of 0.85, while forest B had a D value of 0.35.

Which of the following is the correct conclusion from these results?

  • Forest A has greater biodiversity than forest B.

  • Forest B has higher species richness than forest A.

  • Simpson’s index does not measure biodiversity.

  • Forest B has greater biodiversity than forest A.

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3
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A team of ecologists tracked wolf and moose populations on an island. They found that as wolf numbers increased, moose numbers declined, followed by a decline in wolves due to food scarcity. Later, the moose population began to recover.

Which of the following does this pattern best illustrate?

  • Carrying capacity limitation

  • Predator-prey cycling

  • Density-independent factors

  • Species competition

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4
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A population of rabbits introduced to an island with food and no predators shows rapid initial population growth. Over several years, the population follows an S-shaped curve.

Which of the following types of population growth does this scenario illustrate?

  • Logistic growth

  • Exponential growth

  • Density-independent growth

  • Carrying capacity growth

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1
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Patterns of population growth can be represented by different models, depending on the factors that are acting on a particular population. One population growth model is represented by the equation:

fraction numerator d N over denominator d T end fraction equals r subscript m a x end subscript N

Which of the following growth models, plotted with a linear scale, is represented by the equation provided?

  • Graph showing exponential population growth over time with the x-axis labelled "Time" and the y-axis labelled "Population size".
  • Graph showing population growth over time reaching a stable carrying capacity. The curve's S-shape indicates logistic growth with limits.
  • Line graph showing population size increasing steadily over time, with population size on the vertical axis and time on the horizontal axis.
  • Line graph showing an upward trend of population size over time, with the x-axis labelled "Time" and the y-axis labelled "Population size".

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2
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In the 1800s 24 European rabbits were introduced to Australia. The rabbits encountered abundant resources, little competition and no natural predators in their new environment. Which of the following best describes the initial growth pattern of the rabbit population in Australia?

  • Logistic growth

  • Exponential growth

  • Density-dependent growth

  • Linear growth

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3
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Antarctic fur seals were hunted extensively during the 1800s, and underwent a population recovery following the end of this practice. The recovery of the seal population on Cape Shirreff, Antarctica can be seen in Figure 1 below, where pup count is used to represent the size of the seal population.

Line graph showing pup count from 1960 to 2005, with a sharp increase after 1985, peaking over 7000 around 2000.
Fig. 1. Population growth in Atlantic fur seals between 1960 and the early 2000s.

Which of the following best explains the shape of the seal population growth curve in Fig. 1?

  • The seal population has no constraints on reproduction rate.

  • Death rate exceeds birth rate in the seal population.

  • Rate of reproduction is limited by density-dependent factors but not by density-independent factors.

  • Density-dependent and density-independent factors are limiting the rate of reproduction.

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4
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Simpson’s index of diversity can be calculated using the following formula:

straight D space equals space 1 space minus space straight capital sigma open parentheses n over N close parentheses squared

Sampling of insect species was carried out in a back garden. The results of the sampling are shown in the table:

Species

Number of individuals

Black ants

20

Earthworms

11

Swallowtail butterfly

4

  • 0.4331

  • 0.5669

  • 35

  • 0.3249

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5
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Competition between species occurs when two or more species vie for the same resources. A study was carried out into competition between two species of single-celled organism: P. aurelia and P. caudatum. Figure 1 shows population growth in the two species in the absence of competition.

Graph showing population growth of P. aurelia and P. caudatum over time. P. aurelia stabilises at 200 cells by day 12; P. caudatum stabilises at 60 cells by day 8.
Figure 1. Growth of P. aurelia and P. caudatum in the absence of competition

Which of the following is the most likely outcome if the two species were grown together in the same environment?

  • Graph showing cell populations over 24 days. The black line rises sharply to 150 cells by day 10, while the grey line peaks at 50 cells around day 6.
  • Line graph showing cell population growth over 24 days. The black line peaks at 200 on day 10, while the grey line peaks at 150 on day 12.
  • Line graph showing cell population over 24 days, with two curves: one peaking at 8 days, the other rising steadily to day 16, both between 0-200 cells.
  • Graph of cell population over 24 days showing rapid growth till day 10, peaking at 200 cells, then stabilising.

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1
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A population of elk in a national park initially grows exponentially, but after several decades this growth pattern changes. Researchers tracked population changes and observed fluctuations around a stable population size. Their results are shown in Figure 1.

Line graph showing total elk population from 1978 to 2020, peaking near 600 in 1996 and 2007, with a decline and fluctuations thereafter.
Figure 1. Elk population from 1978 to 2020

Which of the following is the best explanation for the growth pattern shown in Figure 1?

  • Due to limited resources, the declining birth rate and increasing death rate result in dynamic stability around the carrying capacity.

  • Carrying capacity is constantly changing, causing the elk population to be in a dynamic state.

  • Density-independent factors regulate the elk population, slowing growth as population size increases.

  • Competition between elk is eliminated as population size increases, ensuring long-term stability.

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21 mark

Scientists monitored a deer population in two different regions over several years. One region experienced increasing competition for resources as the population increased in size, while the other was affected by severe wildfires. The population changes are recorded in table 1 below:

Table 1. Deer population size in two regions

Year

Region A (resource-limited)

Region B (fire-prone)

Year 1

500

500

Year 3

750

480

Year 5

900

300

Year 7

950

100

Which of the following conclusions best fits the dat population regulation in these two regions?

  • Region A’s population increased by 450 deer between years 1 and 7, confirming that no environmental constraints are limiting growth.

  • Region B’s population decreases by an average of 100 deer per year, showing that density-dependent factors are the primary cause of decline.

  • Region A is affected primarily by density-dependent factors, while region B is affected primarily by density-independent factors.

  • The steady population growth in region A indicates that the population is not approaching carrying capacity.

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31 mark

A lake ecosystem was studied before and after the introduction of an invasive fish species. Researchers measured fish species diversity and oxygen levels over 10 years. The invasive fish species were added in year 2. The results are shown in Figure 1.

Fish species diversity and oxygen levels
Figure 1. Fish species diversity and oxygen levels

Which of the following best describes the relationship between fish species richness and oxygen levels?

  • The 80 % decline in fish species richness correlates with a 43 % decrease in oxygen levels.

  • The observed drop in oxygen levels suggests that the invasive species increased primary productivity, leading to greater oxygen consumption by aerobic decomposers.

  • A greater than 50 % reduction in species richness by year 6 corresponds with only a 26 % decrease in oxygen levels, indicating that biodiversity loss and oxygen levels are independent of each other.

  • Oxygen availability decreased due to an increase in fish respiration, as competition forced them to become more active and consume more oxygen.

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4
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Ecologists conducted a long-term study to assess the impact of planned fires on forest diversity in Wisconsin, USA. The research aimed to determine the importance of fire in maintaining biodiversity in oak forests. In 1996 the forest was split into 15 units; seven units were in a planned fire category, while the remainder served as a control and were not burned. Planned fires were conducted every 1 to 4 years in the burned units. Ecologists compared diversity in the burned units with that of unburned units across four sampling years (1996, 2002, 2007, and 2023).

The results in Figure 1 display the average species diversity per m² during each of the sampling years for both burned and unburned units.

Bar chart showing average species diversity per m2 from 1996 to 2023, comparing burned and unburned units. Diversity decreases over time.
Figure 1. Species diversity in burned and unburned forest units

Which of the following is the most likely conclusion that can be drawn from the data in Figure 1?

  • There is a decrease in forest species diversity over time, indicating that planned fires have a negative impact on biodiversity overall.

  • Areas that have experienced planned fires show significantly higher species diversity than unburned units, but there is an overall decline in species diversity over time.

  • Burned units show higher species diversity than unburned units, but by 2023 diversity declines in both conditions, suggesting that additional ecological factors are limiting diversity.

  • Burned units consistently show higher species diversity than unburned units, demonstrating that planned fire is an effective long-term strategy for maintaining biodiversity in forest ecosystems.

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