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AP Biology Unit 8: Ecology

12 questions

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Unit 8: Ecology

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Question 1

A population of rabbits in an isolated meadow is growing according to the logistic growth model. The carrying capacity (K) is 500 rabbits, and the current population size (N) is 250. Which of the following statements correctly predicts the population growth rate relative to when N = 50?

A.Growth rate is lower at N=250 than at N=50 because density-dependent factors increase as N increasesB.Growth rate is at its maximum when N=250 because N equals K/2C.Growth rate is higher at N=50 than at N=250 because fewer density-dependent constraints existD.Growth rate is equal at N=50 and N=250 because the intrinsic rate of increase (r) is constant

Question 2

A food chain is: grass → rabbit → fox → eagle. If energy transfer efficiency between each trophic level is approximately 10%, and the grass (producers) fix 10,000 kcal of energy, how much energy is available to eagles?

A.1,000 kcalB.10 kcalC.100 kcalD.0.1 kcal

Question 3

Which of the following correctly describes the role of decomposers in a terrestrial ecosystem?

A.They convert sunlight energy into chemical energy stored in organic moleculesB.They break down dead organic matter and return nutrients to the abiotic environmentC.They consume primary producers and transfer energy to higher trophic levelsD.They fix atmospheric nitrogen into ammonium for use by plants

Question 4

The phosphorus cycle, unlike the carbon and nitrogen cycles, lacks a significant atmospheric reservoir. What are the primary environmental consequences of this difference?

A.Phosphorus cycles very rapidly between organisms and the atmosphere, making it rarely limitingB.Phosphorus cycles slowly through geological weathering and is often the limiting nutrient in aquatic ecosystemsC.Phosphorus volatilizes from soil and is replenished regularly by precipitation, similar to nitrogenD.Phosphorus is more abundant than nitrogen in most ecosystems because it does not escape to the atmosphere

Question 5

A species of bird exclusively eats large seeds. Another species of bird exclusively eats small seeds. When they are allopatric (living separately), each species occupies a range of seed sizes. When the two species are sympatric (living together), each species shifts its diet to the extremes (one eats only very large seeds; the other eats only very small seeds). This pattern is best explained by which of the following?

A.Competitive exclusion, where one species is eliminated from the shared habitatB.Character displacement, where competition drives evolutionary divergence in resource useC.Resource partitioning without evolutionary change, where the species simply exploit different microhabitatsD.Mutualism between the two species, where each benefits by avoiding competition over seeds

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Question 6

Ecologists studying a forest community notice that one species of tree (species A) grows quickly and shades other species. Over 50 years, species A is replaced by longer-lived tree species that are shade-tolerant. This process is best described as which of the following?

A.Primary succession, because the change begins with pioneer species colonizing bare substrateB.Secondary succession, where one community replaces another following a disturbanceC.Ecological succession toward a climax community, as early-successional species are replaced by late-successional speciesD.Competitive exclusion, where species A eliminates all other tree species from the community

Question 7

Which of the following describes a density-independent factor that limits population growth?

A.Predation rate increases as prey population density risesB.A severe drought that kills a fixed proportion of organisms regardless of population sizeC.Disease transmission rises as individuals are crowded togetherD.Intraspecific competition for food intensifies as population density increases

Question 8

A group of ecologists introduces a new predator (wolves) into an ecosystem that previously had none. Over the following years, the deer population declines and vegetation in the riparian zone recovers. Beaver populations also increase as vegetation returns. The wolves did not directly interact with beavers. This is an example of which ecological phenomenon?

A.Bottom-up regulation, where primary producers drive changes in higher trophic levelsB.A trophic cascade, where predator addition triggers indirect changes through multiple trophic levelsC.Competitive exclusion between wolves and beavers for shared resourcesD.Character displacement between deer and beavers due to increased competition

Question 9

An invasive grass species is introduced to a prairie ecosystem and rapidly spreads, outcompeting native grasses. Native insect species that depend on native grasses for food and reproduction begin to decline. Which of the following best describes the mechanism by which the invasive grass is harming native insects?

A.The invasive grass directly predates on native insectsB.Habitat and food resource loss from competitive displacement of native plants causes indirect harm to dependent insectsC.The invasive grass produces toxins that directly kill native insectsD.Native insects voluntarily migrate away because they prefer habitats with lower plant diversity

Question 10

A researcher measures the carbon flux in a forest ecosystem. She finds that gross primary productivity (GPP) is 8,000 g C/m²/year and plant respiration is 3,500 g C/m²/year. She also measures that herbivores consume 1,000 g C/m²/year of plant biomass, and decomposers respire 2,500 g C/m²/year. Which of the following correctly calculates the net primary productivity (NPP) and identifies whether this ecosystem is a net carbon sink or source?

A.NPP = 4,500 g C/m²/year; the ecosystem is a carbon sink because NPP exceeds decomposer respirationB.NPP = 4,500 g C/m²/year; the ecosystem is a carbon source because total respiration exceeds GPPC.NPP = 3,000 g C/m²/year; the ecosystem is carbon neutral because NPP equals herbivore consumption plus decomposer respirationD.NPP = 8,000 g C/m²/year; plant respiration is not subtracted because it is already included in GPP

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Question 11

In the nitrogen cycle, which group of organisms is responsible for converting ammonium ( $N H_{4}^{+}$ ) into nitrite ( $N O_{2}^{-}$ ) and then nitrate ( $N O_{3}^{-}$ )?

A.Denitrifying bacteriaB.Nitrifying bacteriaC.Nitrogen-fixing bacteriaD.Decomposers

Question 12

Mycorrhizal fungi form associations with plant roots, providing phosphorus to the plant in exchange for carbohydrates. Which type of species interaction does this represent?

A.Commensalism (+/0): the fungus benefits and the plant is unaffectedB.Mutualism (+/+): both the fungus and the plant benefit from the associationC.Parasitism (+/−): the fungus benefits and the plant is harmedD.Amensalism (0/−): the fungus is unaffected and the plant is harmed

AP Biology Unit 8: Ecology — Free with Answer Explanations | Test Practice Hub