Rucete ✏ AP Biology In a Nutshell
21. Population Ecology, Community Ecology, and Biodiversity — Practice Questions 2
This chapter explores population dynamics, interspecies interactions in ecosystems, and how biodiversity contributes to ecological stability and resilience.
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(Multiple Choice — Click to Reveal Answer)
1. Which of the following best defines population density?
(A) Number of births per generation
(B) Number of organisms per unit area
(C) Number of species in a region
(D) Biomass per hectare
Answer
(B) — Population density measures how many individuals live within a given area.
2. What is the most likely result of low genetic diversity in a population?
(A) Higher birth rate
(B) Increased adaptability
(C) Greater vulnerability to disease
(D) Better predator defense
Answer
(C) — Low genetic diversity reduces a population’s ability to adapt to new challenges, including disease.
3. Which of the following is a method of estimating population size in the field?
(A) Quadrat sampling
(B) Biomass analysis
(C) Fossil excavation
(D) Trophic mapping
Answer
(A) — Quadrat sampling involves counting individuals within randomly placed squares to estimate total population size.
4. What is a common characteristic of mutualism?
(A) Both organisms are harmed
(B) One benefits, the other is unaffected
(C) Both organisms benefit
(D) One benefits, one is harmed
Answer
(C) — Mutualism is a +/+ interaction where both organisms gain from the relationship.
5. A climax community is typically:
(A) Early in ecological succession
(B) Highly unstable
(C) Temporarily dominated by r-selected species
(D) Stable and long-lasting until disturbed
Answer
(D) — Climax communities are relatively stable and persist unless disturbed by major environmental changes.
6. Which type of dispersion pattern is common in territorial species?
(A) Random
(B) Clumped
(C) Uniform
(D) Vertical
Answer
(C) — Territorial species often space themselves evenly to defend resources, creating a uniform distribution.
7. Which of the following best defines interspecific competition?
(A) Competition among same-species individuals
(B) Competition between members of a food chain
(C) Competition between different species
(D) Competition between parent and offspring
Answer
(C) — Interspecific competition occurs between individuals of different species competing for the same resources.
8. What is the primary limiting factor for growth in a dense forest ecosystem?
(A) Soil temperature
(B) Light availability
(C) Atmospheric pressure
(D) Wind speed
Answer
(B) — In dense forests, light is often limited due to canopy cover, restricting plant growth.
9. Which of the following describes a food web?
(A) A diagram of water flow
(B) A diagram showing how energy flows through multiple feeding relationships
(C) A chart of reproductive cycles
(D) A linear sequence of predator-prey relationships
Answer
(B) — A food web shows interconnected feeding relationships among multiple organisms in an ecosystem.
10. Which of the following typically leads to secondary succession?
(A) Volcanic eruption forming new land
(B) Retreat of a glacier
(C) A forest fire
(D) Floodplain uplift
Answer
(C) — Secondary succession occurs when an existing community is disturbed but soil remains intact, such as after a fire.
11. What does the term “biotic potential” refer to?
(A) Energy storage capacity
(B) Ability of a habitat to sustain life
(C) Maximum reproductive capacity of a species
(D) Number of available ecological niches
Answer
(C) — Biotic potential is the theoretical maximum rate at which a population can increase under ideal conditions.
12. Which of the following species is most likely to follow a boom-and-bust population cycle?
(A) Elephant
(B) Wolf
(C) Mouse
(D) Gorilla
Answer
(C) — r-selected species like mice reproduce rapidly and often show large population swings.
13. Which ecological factor does not vary with population density?
(A) Disease transmission
(B) Resource competition
(C) Earthquakes
(D) Predation pressure
Answer
(C) — Earthquakes are density-independent events that impact populations regardless of size.
14. What type of symbiotic relationship is exemplified by barnacles growing on a whale?
(A) Mutualism
(B) Parasitism
(C) Commensalism
(D) Predation
Answer
(C) — Barnacles benefit by gaining mobility and access to nutrients, while the whale is unaffected.
15. What usually determines the carrying capacity of an environment for a population?
(A) Genetic mutations
(B) Environmental resistance
(C) Predator migration
(D) Atmospheric oxygen
Answer
(B) — Carrying capacity is set by resource availability and environmental constraints (i.e., environmental resistance).
16. In which environment would you expect the highest biodiversity?
(A) Polar tundra
(B) Desert scrub
(C) Temperate deciduous forest
(D) Tropical rainforest
Answer
(D) — Tropical rainforests have high temperature and moisture levels, promoting extremely high biodiversity.
17. Which of the following is a trait typical of r-selected species?
(A) Long gestation
(B) Stable population sizes
(C) Early reproductive age
(D) Low offspring mortality
Answer
(C) — r-selected species mature quickly and produce many offspring in a short time.
18. What is one benefit of biodiversity for ecosystems?
(A) Faster extinction rates
(B) Lower genetic mutation
(C) Greater stability and resilience
(D) Higher energy loss
Answer
(C) — Diverse ecosystems are better able to resist and recover from disturbances.
19. What term describes the role an organism plays in its environment?
(A) Biomass
(B) Habitat
(C) Niche
(D) Community
Answer
(C) — An organism’s niche includes its role, interactions, and use of resources in an ecosystem.
20. Which group of organisms is responsible for most decomposition in ecosystems?
(A) Carnivores
(B) Primary consumers
(C) Decomposers
(D) Omnivores
Answer
(C) — Decomposers like fungi and bacteria recycle nutrients by breaking down dead matter.
21. Which factor most directly causes logistic growth curves to level off?
(A) Unlimited space
(B) Abiotic resistance
(C) Reaching carrying capacity
(D) Mutation rate
Answer
(C) — Logistic growth slows as a population nears carrying capacity due to resource limitation.
22. Which of the following is NOT part of community ecology?
(A) Predation
(B) Nutrient cycling
(C) Mutualism
(D) Competition
Answer
(B) — Nutrient cycling is a process involving abiotic and biotic components, typically part of ecosystem, not just community, ecology.
23. Which of the following would be a direct measure of biodiversity?
(A) Number of offspring per adult
(B) Number of ecosystems in a region
(C) Number of species present in an area
(D) Total energy transfer efficiency
Answer
(C) — Biodiversity includes species richness, which is the number of species in a given area.
24. What is one direct consequence of invasive species introduction?
(A) Increase in genetic diversity
(B) Improved ecosystem services
(C) Disruption of native food webs
(D) Acceleration of succession
Answer
(C) — Invasive species often outcompete or displace native species, altering the food web and ecosystem structure.
25. Which characteristic is typical of a climax community?
(A) Rapid turnover of species
(B) Frequent disturbance
(C) High species stability and equilibrium
(D) Low levels of biomass
Answer
(C) — Climax communities are stable, diverse, and maintain equilibrium unless disturbed.
26. Which type of growth model assumes limited resources and a carrying capacity?
(A) Exponential
(B) Geometric
(C) Logistic
(D) Linear
Answer
(C) — Logistic growth incorporates resource limitations, producing an S-shaped curve that levels off at carrying capacity.
27. A sharp decline in population size due to environmental catastrophe followed by low genetic variation is an example of:
(A) Founder effect
(B) Genetic drift
(C) Bottleneck effect
(D) Hardy-Weinberg equilibrium
Answer
(C) — The bottleneck effect occurs when population size is drastically reduced, leading to decreased genetic diversity.
28. Which interaction describes a relationship where one species benefits and the other is harmed, but not killed immediately?
(A) Predation
(B) Competition
(C) Mutualism
(D) Parasitism
Answer
(D) — In parasitism, the parasite benefits while the host is harmed gradually.
29. Which factor would most likely destabilize a biological community?
(A) High species richness
(B) Presence of generalist predators
(C) Loss of a keystone species
(D) Niche partitioning
Answer
(C) — Keystone species maintain ecosystem structure; their removal can lead to ecological collapse.
30. Which concept explains how similar species can coexist in the same environment?
(A) Competitive exclusion principle
(B) Resource partitioning
(C) Carrying capacity
(D) Predator-prey cycle
Answer
(B) — Resource (niche) partitioning allows similar species to divide resources and reduce direct competition.
31. Why is species richness generally higher near the equator than at the poles?
(A) Higher mutation rates
(B) Less seasonal variation and more energy input
(C) Greater rainfall at the poles
(D) More predators to control populations
Answer
(B) — Tropical regions receive consistent sunlight and stable climates, promoting species diversification.
32. Which term describes the ability of an ecosystem to return to equilibrium after a disturbance?
(A) Resistance
(B) Tolerance
(C) Resilience
(D) Redundancy
Answer
(C) — Resilience is an ecosystem's capacity to recover from disturbance and return to its original state.
33. What is the effect of edge habitat on biodiversity?
(A) Increases interior species
(B) Always increases species richness
(C) Can alter species composition and increase invasives
(D) Has no measurable effect
Answer
(C) — Edge habitats may favor invasive species and generalists, reducing habitat quality for specialists.
34. Which of the following best describes the intermediate disturbance hypothesis?
(A) Frequent disturbances maintain climax communities
(B) No disturbance leads to the greatest biodiversity
(C) Moderate levels of disturbance promote the highest biodiversity
(D) All disturbances reduce biodiversity equally
Answer
(C) — According to the intermediate disturbance hypothesis, moderate disturbances allow for both colonizers and competitors to coexist.
35. In metapopulation dynamics, which patch type is most important for long-term survival of a species?
(A) Isolated patches
(B) Sink patches
(C) Source patches
(D) Patches near water
Answer
(C) — Source patches produce surplus individuals that can migrate to sink patches, sustaining the metapopulation.
36. Explain how density-dependent factors regulate population size.
Answer
Density-dependent factors, such as disease, competition, and predation, increase in intensity as population size grows, slowing or reversing population growth near carrying capacity.
37. Describe the role of ecological niches in reducing competition between species.
Answer
Ecological niches define a species’ role and resource use in an ecosystem. By occupying different niches, species avoid direct competition and can coexist.
38. How can biodiversity contribute to ecosystem productivity?
Answer
High biodiversity means more species performing different ecological roles, which can enhance resource use, nutrient cycling, and energy flow, leading to greater ecosystem productivity.
39. What is meant by "species richness" and how is it measured?
Answer
Species richness is the total number of different species in a defined area. It is measured by counting species present without regard to population size.
40. Define "biotic resistance" and give an example.
Answer
Biotic resistance refers to the ability of native species in a community to limit the success of invasive species, often through competition or predation.
41. How does immigration affect population dynamics in an open population model?
Answer
Immigration introduces new individuals and genetic diversity, which can increase population size and adaptability, especially after local declines.
42. Why is the removal of a keystone species often followed by ecosystem collapse?
Answer
Keystone species have a disproportionately large impact on ecosystem structure. Their removal can lead to trophic cascades, loss of diversity, and destabilization of the entire system.
43. Describe how invasive species can alter community structure.
Answer
Invasive species often outcompete or prey on native species, leading to reduced biodiversity, altered food webs, and disrupted nutrient cycling.
44. How can human activity accelerate ecological succession?
Answer
Humans can disturb environments through activities like agriculture, logging, or fire, resetting succession and altering species composition and soil structure.
45. What is meant by "ecological redundancy" and how does it relate to stability?
Answer
Ecological redundancy occurs when multiple species perform similar functions. If one is lost, others can fill its role, increasing ecosystem stability.
46. Define "founder effect" and its consequence on genetic variation.
Answer
The founder effect occurs when a small group colonizes a new area, carrying only a subset of the original gene pool, often leading to reduced genetic diversity.
47. How does species evenness differ from species richness?
Answer
Species evenness refers to the relative abundance of species in a community, while richness is the number of different species present.
48. What is an ecological corridor and why is it important?
Answer
An ecological corridor is a strip of habitat connecting isolated patches, allowing gene flow, migration, and increased species survival in fragmented landscapes.
49. How does climate change influence species distribution?
Answer
Climate change alters temperature and precipitation patterns, causing species to shift ranges, migrate, or face extinction if they cannot adapt or move.
50. Why are generalist species more successful in disturbed environments?
Answer
Generalists can utilize a wide range of resources and tolerate varied conditions, allowing them to thrive where specialists may fail after disturbances.