Rucete ✏ AP Biology In a Nutshell
21. Population Ecology, Community Ecology, and Biodiversity — Practice Questions
This chapter explores how populations grow, how communities interact, and how biodiversity contributes to the stability and resilience of ecosystems.
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(Multiple Choice — Click to Reveal Answer)
1. Which of the following best describes a K-selected species?
(A) Produces many offspring with little parental care
(B) Experiences frequent population crashes
(C) Has long life spans and invests in few offspring
(D) Reproduces only once in a lifetime
Answer
(C) — K-selected species are adapted to stable environments and invest heavily in offspring survival.
2. A population of 100 deer grows exponentially at a rate of 0.1 per year. What is the expected size after 1 year?
(A) 100
(B) 105
(C) 110
(D) 120
Answer
(C) — N = 100, r = 0.1 → Growth = 100 × 0.1 = 10 → Final population = 100 + 10 = 110.
3. What is the primary factor that limits exponential growth in natural populations?
(A) Genetic diversity
(B) Time of reproduction
(C) Environmental resistance
(D) Photosynthesis
Answer
(C) — Exponential growth is only possible without limits, but environmental factors eventually limit population size.
4. Which interaction benefits one species while harming another?
(A) Commensalism
(B) Mutualism
(C) Parasitism
(D) Niche partitioning
Answer
(C) — Parasitism benefits the parasite and harms the host.
5. In a food web, what would most likely happen if a keystone species is removed?
(A) Biodiversity increases dramatically
(B) Only one trophic level is affected
(C) The structure of the entire ecosystem may collapse
(D) Producers go extinct
Answer
(C) — Keystone species have a disproportionate impact on ecosystem stability; removing them can cause cascading effects.
6. Which of the following is an example of density-dependent population regulation?
(A) Earthquake
(B) Competition for food
(C) Seasonal flooding
(D) Fire caused by lightning
Answer
(B) — Density-dependent factors like competition intensify as population size increases.
7. What is the primary cause of logistic population growth slowing as it nears carrying capacity?
(A) Decreased reproduction rates
(B) Increased immigration
(C) Abiotic disturbances
(D) Limited resources
Answer
(D) — As population reaches carrying capacity, resources such as food and space become limited, slowing growth.
8. Which type of survivorship curve is most characteristic of large mammals like elephants?
(A) Type I
(B) Type II
(C) Type III
(D) Exponential
Answer
(A) — Type I curves show low mortality early in life, with most deaths occurring in older individuals.
9. What term describes the variety of all species in an ecosystem?
(A) Biomass
(B) Genetic drift
(C) Biodiversity
(D) Mutualism
Answer
(C) — Biodiversity refers to the variety of living organisms in a given area.
10. Which of the following would most likely lead to primary succession?
(A) Forest fire
(B) Plowed agricultural field
(C) Glacial retreat
(D) Abandoned urban park
Answer
(C) — Primary succession begins in lifeless areas without soil, such as after glacial retreat.
11. What is the function of a pioneer species during ecological succession?
(A) Provide shade
(B) Introduce predators
(C) Modify the environment to make it habitable
(D) Outcompete all species
Answer
(C) — Pioneer species improve conditions (e.g., soil formation) to enable other species to colonize.
12. A population in which all individuals have an equal chance of dying at any age is represented by:
(A) Type I curve
(B) Type II curve
(C) Type III curve
(D) Exponential model
Answer
(B) — Type II survivorship shows constant mortality risk throughout life.
13. Which of the following most directly increases species richness in a habitat?
(A) Habitat fragmentation
(B) Climate change
(C) Introduction of barriers
(D) Increased habitat complexity
Answer
(D) — Diverse and complex habitats support more niches, leading to greater species richness.
14. What is a biological community?
(A) A group of organisms of the same species
(B) All organisms living in a specific area
(C) All abiotic factors in a region
(D) All members of a trophic level
Answer
(B) — A community includes all interacting organisms in a particular area, regardless of species.
15. A population crash due to overconsumption of resources is an example of:
(A) Mutualism
(B) Ecological resilience
(C) Overshoot
(D) Keystone release
Answer
(C) — When a population exceeds carrying capacity, resource depletion may cause a sharp decline (overshoot and collapse).
16. Which process allows multiple species to share resources in a stable environment?
(A) Competitive exclusion
(B) Niche partitioning
(C) Biomagnification
(D) Keystone predation
Answer
(B) — Niche partitioning reduces direct competition by dividing resource use among species.
17. What is the ecological role of decomposers in a community?
(A) Convert nitrogen to nitrates
(B) Consume sunlight directly
(C) Break down organic matter and recycle nutrients
(D) Hunt herbivores
Answer
(C) — Decomposers return nutrients to the soil and help maintain nutrient cycling.
18. Which of the following is an r-selected trait?
(A) Long gestation
(B) High parental care
(C) Rapid development
(D) Few offspring
Answer
(C) — r-selected species reproduce quickly and produce many offspring with little investment in each.
19. What does species evenness measure?
(A) The number of different species
(B) The genetic variation within a population
(C) The relative abundance of each species
(D) The total biomass of a species
Answer
(C) — Species evenness refers to how evenly individuals are distributed among species in a community.
20. Which of the following best defines a climax community?
(A) A community in which all species are r-selected
(B) A stable, mature community that undergoes little change
(C) A community with no producers
(D) The first stage of succession
Answer
(B) — A climax community is stable and remains relatively unchanged until a disturbance occurs.
21. Which factor is most likely to increase genetic diversity within a population?
(A) Bottleneck effect
(B) Founder effect
(C) High mutation rate
(D) Small population size
Answer
(C) — Mutations introduce new alleles and increase genetic diversity over time.
22. A parasitic relationship is an example of which type of interaction?
(A) +/+
(B) +/−
(C) −/−
(D) 0/0
Answer
(B) — Parasitism benefits one species and harms the other.
23. Which term describes all living and nonliving components in an area?
(A) Community
(B) Ecosystem
(C) Biome
(D) Trophic level
Answer
(B) — An ecosystem includes both biotic (living) and abiotic (nonliving) components.
24. Which interaction increases biodiversity by preventing competitive exclusion?
(A) Symbiosis
(B) Predator-mediated coexistence
(C) Commensalism
(D) Parasitism
Answer
(B) — Predators can keep dominant competitors in check, allowing weaker species to survive and maintain diversity.
25. What does a survivorship curve illustrate?
(A) The reproductive rate
(B) The lifespan of an ecosystem
(C) The likelihood of death at various ages
(D) The energy efficiency of a population
Answer
(C) — Survivorship curves show how mortality rates change with age in a population.
26. In logistic population growth, what happens when the population exceeds the carrying capacity?
(A) The population grows faster
(B) The population crashes due to resource depletion
(C) The growth rate becomes zero
(D) The birth rate increases further
Answer
(B) — When populations exceed carrying capacity, resources become overused, leading to population crashes or decline.
27. Which factor most directly affects the resilience of a biological community?
(A) Temperature extremes
(B) Species richness and diversity
(C) Amount of rainfall
(D) Latitude and altitude
Answer
(B) — Communities with higher biodiversity tend to be more resilient to disturbances because multiple species can fulfill similar roles.
28. Why are K-selected species more vulnerable to extinction than r-selected species?
(A) They are smaller and less mobile
(B) They rely on abiotic reproduction
(C) They produce few offspring and have slow recovery rates
(D) They thrive in disturbed environments
Answer
(C) — K-selected species reproduce slowly and invest heavily in few offspring, making recovery from population loss difficult.
29. Which of the following is a likely outcome of competitive exclusion?
(A) Both species increase in number
(B) The two species evolve to become mutualists
(C) One species is eliminated from the habitat
(D) Both species benefit from shared resources
Answer
(C) — The competitive exclusion principle states that two species competing for the same resource cannot coexist indefinitely; one will outcompete the other.
30. How does edge effect influence species diversity in fragmented habitats?
(A) It increases sunlight and supports large predators
(B) It creates conditions that benefit generalist species
(C) It stabilizes microclimates and reduces competition
(D) It promotes reproductive isolation of interior species
Answer
(B) — Edges create transitional zones that often favor generalists and invasive species, sometimes reducing overall interior diversity.
31. Which characteristic would increase a population's biotic potential?
(A) Long lifespan
(B) Late reproductive age
(C) Large number of offspring per reproductive event
(D) Extensive parental care
Answer
(C) — Populations with high biotic potential reproduce quickly, producing many offspring in a short time.
32. What does the Shannon diversity index account for when measuring biodiversity?
(A) Only the number of species
(B) Genetic variation within a species
(C) Species richness and evenness
(D) Total population size
Answer
(C) — The Shannon index measures both how many species are present (richness) and how evenly individuals are distributed (evenness).
33. In a population regulated primarily by density-dependent factors, what would be expected as population density increases?
(A) Lower disease transmission
(B) Higher per capita growth rate
(C) Increased competition and resource scarcity
(D) Fewer predator-prey interactions
Answer
(C) — As population density rises, resources become scarce, and competition, disease, and predation increase.
34. What ecological principle is supported by the diversity-stability hypothesis?
(A) Less competition leads to more stability
(B) Communities with more species are more resistant to disturbance
(C) Keystone species decrease diversity
(D) Productivity always increases with species loss
Answer
(B) — The diversity-stability hypothesis proposes that diverse ecosystems are better able to resist and recover from environmental changes.
35. Which of the following human activities is most directly responsible for habitat fragmentation?
(A) Climate change
(B) Introduction of non-native species
(C) Deforestation for agriculture and urbanization
(D) Overharvesting marine organisms
Answer
(C) — Clearing land for agriculture or development breaks large habitats into smaller patches, fragmenting ecosystems.
36. Define carrying capacity and explain how it affects population dynamics.
Answer
Carrying capacity is the maximum number of individuals an environment can support sustainably. When a population approaches this limit, growth slows due to limited resources, and populations may fluctuate around this point.
37. What is niche partitioning and how does it promote species coexistence?
Answer
Niche partitioning occurs when species divide resources by using different areas, times, or methods, reducing direct competition and allowing coexistence within the same habitat.
38. How can biodiversity increase ecosystem resilience?
Answer
Biodiversity allows ecosystems to better absorb disturbances, as multiple species can perform similar ecological roles, maintaining stability even if some species are lost.
39. Describe the difference between Type I and Type III survivorship curves and give an example of each.
Answer
Type I curves show low early mortality (e.g., humans), while Type III curves show high early mortality (e.g., fish or insects). These reflect different life history strategies.
40. What ecological role do keystone species play in their communities?
Answer
Keystone species maintain community structure by regulating population sizes or influencing resource availability; their removal often causes significant ecosystem disruption.
41. Explain how human activities can lead to habitat fragmentation and its effects.
Answer
Activities like urban development or deforestation break ecosystems into smaller patches, isolating species, reducing genetic diversity, and increasing edge effects.
42. How does predation help maintain biodiversity in a community?
Answer
Predation prevents dominant species from excluding others, allowing multiple species to coexist and maintain diversity through top-down control.
43. Why are pioneer species important in primary succession?
Answer
Pioneer species colonize bare areas, modifying the environment (e.g., adding organic material, breaking rock) to allow other species to establish.
44. How does species richness differ from species evenness?
Answer
Species richness is the number of different species present, while evenness describes how equally individuals are distributed among those species.
45. Describe how edge effects influence organisms living near habitat boundaries.
Answer
Edge effects expose organisms to altered conditions (e.g., more light, temperature variation, predators), which can benefit generalists but harm species adapted to interior environments.
46. What is the role of decomposers in maintaining community structure?
Answer
Decomposers recycle nutrients from dead organisms, maintaining soil fertility and enabling producers to support food webs.
47. Explain how density-dependent and density-independent factors regulate population size.
Answer
Density-dependent factors (e.g., competition, disease) intensify with population size, while density-independent factors (e.g., weather events) affect populations regardless of size.
48. How does intraspecific competition affect population growth?
Answer
Intraspecific competition for limited resources reduces individual fitness and can slow or stabilize population growth near carrying capacity.
49. What is meant by ecological succession?
Answer
Ecological succession is the gradual change in species composition of a community over time, often progressing from pioneer species to a stable climax community.
50. How do r-selected and K-selected species differ in reproductive strategy?
Answer
r-selected species reproduce quickly with many offspring and low survival rates, while K-selected species invest more in fewer offspring with high survival and stable population sizes.