AP Environmental Science Unit 3 practice questions
Try 10 multiple-choice questions from Unit 3 here. Pick an answer to see why it's right or wrong, then take the timed test above for a full AP-style set.
Question 1
Deforestation fragments a tropical rainforest into patches separated by agriculture. Harpy eagles that hunt canopy mammals and need large continuous territories vanish within five years, while coyotes establish populations in agricultural zones. Which explanation best accounts for their different responses to fragmentation?
Harpy eagles are habitat specialists and coyotes are generalist resource exploiters.
Harpy eagles need more food energy than coyotes because of larger body size.
Harpy eagles reproduce more slowly than coyotes, limiting recolonization of patches.
Differences in visual acuity determine predator success across open versus forest habitats.
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Answer: (A)
Specialist habitat and prey requirements make harpy eagles vulnerable when forests fragment. Coyotes' broad diet and habitat tolerance let them use agricultural mosaics and persist.
Question 2
A tick species depends on large savanna mammals. Drought reduces those hosts by 70 percent. Tick numbers fall then stabilize at lower levels rather than collapse. Which explanation best accounts for tick persistence despite the host decline?
Surviving mammals cluster at water sources, increasing local host density and tick encounters.
Rapid evolution boosting tick reproduction is unlikely to occur during one drought.
Widespread stronger host immunity would cause continued decline instead of a stable population.
Ticks switching to smaller mammals and birds would likely restore or raise numbers.
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Answer: (A)
Host aggregation increases local encounter rates so parasites persist despite fewer total hosts. Concentration at water sources provides enough blood meals to maintain a smaller stable tick population.
Question 3
Researchers studying intraspecific competition measured only population-level averages (total population size and average growth rate) in high-density and low-density populations of the same species. If they modified the procedure to measure individual growth rates and survival across both density conditions, how would this change most likely affect their understanding of how resource scarcity influences competition?
Measuring individual-level fitness would reveal how resource scarcity intensifies intraspecific competition and reduces individual growth and survival in high-density populations.
Measuring individual-level fitness would require more time and resources to collect data, increasing study costs without providing additional ecological insights.
Measuring individual-level fitness would show that individual growth and survival are identical regardless of population density because genetic factors determine fitness.
Measuring individual-level fitness would only reveal competition effects if the study includes laboratory populations rather than natural populations where environmental variation masks density-dependent patterns.
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Answer: (A)
Recognizing that individual-level measurement reveals competition mechanisms. Population-level averages mask variation in how individuals are affected by competition; individual measurements show that limited resources (food, space, light) create stronger competition at high density, reducing individual fitness. This directly tests LO 1.1-A by demonstrating how resource availability influences intraspecific competition intensity and individual outcomes.
Question 4
In the Serengeti savanna, lions and hyenas are both predators of zebras. When lion populations declined due to disease, zebra populations initially increased. However, after two years, zebra populations declined sharply despite continued low lion numbers. Which of the following best explains this delayed decline in zebra populations?
Increased zebra populations overconsumed grass, reducing vegetation below the carrying capacity threshold, which then limited zebra population growth and caused decline
Increased zebra populations led to higher population density, which facilitated disease transmission among zebras, causing population decline after a two-year incubation period
Increased zebra populations overconsumed grass, reducing vegetation below the carrying capacity threshold, which then stabilized zebra populations at a new, lower equilibrium rather than causing decline
Grass vegetation declined due to two years of drought stress in the savanna, reducing food availability below the threshold needed to support increased zebra populations, which then caused zebra decline
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Answer: (A)
This explanation requires understanding negative feedback in food webs: predator removal → prey increase → overgrazing → vegetation depletion → prey starvation → prey decline. The two-year delay reflects the time required for vegetation to be depleted and for nutritional stress to reduce zebra survival and reproduction. This demonstrates how food webs regulate themselves through resource limitation when top-down control (predation) is removed.
Question 5
Endemic specialist mammals on an island produce an average of 2 offspring per year with 80% survival to reproductive age, while invasive generalist mammals produce an average of 4 offspring per year with 90% survival to reproductive age. A population ecologist wants to predict which group will increase in abundance and eventually dominate the island. Which quantitative approach would best support this prediction?
Calculate the intrinsic rate of increase (population growth rate) for both endemic and invasive populations using reproductive rate and survival data, then compare growth rates to predict which population will increase faster and dominate
Calculate the intrinsic rate of increase (population growth rate) for both endemic and invasive populations using reproductive rate data, then compare growth rates to predict which population will increase faster and dominate
Calculate the intrinsic rate of increase (population growth rate) for both endemic and invasive populations using reproductive rate and survival data, then compare which population has higher absolute reproductive success
Calculate the intrinsic rate of increase (population growth rate) for both endemic and invasive populations using reproductive rate and survival data, then compare growth rates to predict which population will reach carrying capacity first
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Answer: (A)
The intrinsic rate of increase incorporates both reproductive output and survival, providing a comprehensive measure of population growth potential. Comparing growth rates directly predicts population trajectories—the invasive's higher growth rate (4 offspring × 0.90 survival > 2 offspring × 0.80 survival) indicates faster population increase and eventual dominance. This method quantifies why generalists outcompete specialists: generalists have higher population growth rates that allow them to increase in abundance despite initial lower numbers.
Question 6
An island ecosystem contains three native specialist herbivore species, each feeding on a different plant species. A generalist herbivore is introduced to the island and rapidly increases in population, consuming all three plant species at high rates. Within two years, all three specialist herbivores are extinct, but the generalist herbivore population then declines sharply and stabilizes at a low level. Which of the following best explains why the generalist herbivore population declined after eliminating the specialist competitors?
The generalist herbivore overexploited all three plant species, reducing plant populations below the level needed to sustain the generalist's large population, resulting in a new equilibrium at lower herbivore density.
The generalist herbivore population increased to high density, intensifying intraspecific competition for the three plant species, resulting in a new equilibrium at lower herbivore density.
The generalist herbivore overexploited all three plant species, reducing plant populations below the level needed to sustain the generalist's large population, resulting in cyclical oscillations between herbivore and plant populations.
The generalist herbivore overexploited one primary plant species that provided most of its nutrition, reducing that plant population below the level needed to sustain the generalist's large population, resulting in a new equilibrium at lower herbivore density.
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Answer: (A)
Applying island biogeography to multi-species dynamics requires understanding resource limitation and carrying capacity. The three specialist herbivores each maintained sustainable populations by specializing on specific plants; their extinction removed this resource partitioning. The generalist, lacking specialization, exploits all plants indiscriminately and rapidly depletes the total plant biomass available. The plant populations crash below the level supporting the generalist's initial population size, forcing the herbivore population to decline to a new equilibrium. This demonstrates that generalists' competitive advantage (ability to exploit diverse resources) becomes a liability when resources are limited, as generalists deplete resources faster than specialists would.
Question 7
A park restricts human access to a remote alpine meadow to protect a specialist plant with a narrow elevation range. Average temperatures rise by 2°C. Which outcome is an unintended consequence of this protection strategy?
The plant cannot find higher suitable habitat and declines despite protection.
The plant will rapidly evolve tolerance to warmer temperatures and expand.
The specialist will outcompete generalists moving upslope as conditions change.
Restricting human access eliminates all environmental stress on the plant.
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Answer: (A)
Specialist species have narrow niches and cannot track warming if suitable higher habitat is limited. Mountains have finite elevation so protection from human disturbance cannot prevent range loss.
Question 8
River otter populations have declined in many regions where rivers have been dammed and polluted, while populations of generalist predators like raccoons have remained stable or increased. Which of the following best explains this difference in population responses?
The river otter's specialization on fish and freshwater habitats means it requires clean, flowing water with adequate fish populations; when rivers are dammed or polluted, otter populations decline because they cannot switch to alternative prey or habitats like generalist predators can.
The river otter's territorial behavior and specialization on fish and freshwater habitats means it requires large, exclusive home ranges along rivers; when rivers are dammed or polluted, otter populations decline because their territorial requirements prevent them from adapting to smaller habitat patches like generalist predators can.
The river otter's specialization on fish and freshwater habitats means it requires clean, flowing water with adequate fish populations; when rivers are dammed or polluted, otter populations initially decline but then recover as otters adapt their foraging strategies, unlike generalist predators that maintain stable populations throughout.
The river otter's specialization on fish and freshwater habitats means it requires clean, flowing water with adequate fish populations; when rivers are dammed or polluted, otter populations decline primarily because generalist predators increase in number and outcompete otters for limited fish resources.
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Answer: (A)
Linking dietary and habitat specialization to vulnerability during environmental degradation reveals the mechanism of specialist disadvantage. River otters' dependence on specific prey (fish) and habitat conditions (clean, flowing water) creates inflexibility when those conditions deteriorate, whereas generalists like raccoons can exploit alternative food sources and tolerate degraded habitats—this directly demonstrates the EK principle that specialists are disadvantaged when habitats change.
Question 9
Koala numbers drop when eucalyptus forests are cleared. Why can't koalas persist while generalist herbivores like deer do in the same areas?
Koalas specialize on eucalyptus and cannot switch to other plants.
Mistakenly identifies the giant panda as a dietary generalist.
Attributes decline to body size or density rather than dietary inflexibility.
Claims specialization protects koalas from competition and ensures survival.
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Answer: (A)
Koalas depend almost exclusively on eucalyptus and lack the digestive flexibility to use other plants. Generalist herbivores can eat many species or move, allowing them to persist after habitat change.
Question 10
Urban areas offer variable food, fluctuating temperatures, and unpredictable shelter. Why do generalists thrive there while specialists rarely establish populations?
Generalists tolerate varied diets and conditions so they persist in cities.
Faster reproduction aids spread but does not explain urban tolerance.
This reverses the pattern by claiming generalists dominate stable forests.
Specialists fail because unpredictable resources and conditions exceed narrow tolerances.
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Answer: (A)
Broad tolerance of diet and microclimate lets generalists survive urban unpredictability. Flexible diets and tolerance of temperature and shelter variation reduce reliance on specific habitats or food sources.
What's on the AP Environmental Science Unit 3 practice test
The standard version takes about 70 minutes and follows the timing and directions of the AP exam, sized to one unit:
- 20 Multiple Choice Questions (23 minutes)
- 1 FRQ – FRQ 1 – Design an Investigation (23 minutes)
- 1 FRQ – FRQ 2 – Analyze and Interpret Quantitative Data (23 minutes)
Questions are drawn from 2465 multiple-choice questions and 42 FRQs written for Unit 3, Populations.
Practice AP Environmental Science Unit 3 FRQs
Answer the unit's free-response questions one at a time and get a score on every part.
- FRQ 1 – Design an Investigation (16 questions)
- FRQ 2 – Analyze and Interpret Quantitative Data (13 questions)
- FRQ 3 – Analyze an Environmental Problem Doing Calculations (13 questions)
Review Unit 3 before you start
- 3.1 Generalist and Specialist Species
- 3.2 K-Selected r-Selected Species
- 3.3 Survivorship Curves
- 3.4 Carrying Capacity
- 3.5 Population Growth and Resource Availability
- 3.6 Age Structure Diagrams
- 3.7 Total Fertility Rate
- 3.8 Human Population Dynamics
- 3.9 Demographic Transition