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21. Population Ecology, Community Ecology, and Biodiversity — Practice Questions 3
This chapter explores how population growth, species interactions, and ecosystem diversity contribute to ecological balance and resilience.
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(Multiple Choice — Click to Reveal Answer)
1. Which of the following is a characteristic of a population?
(A) Number of ecosystems
(B) Individuals of the same species in a given area
(C) Variety of habitats
(D) Range of biomes
Answer
(B) — A population consists of individuals of the same species living in the same area.
2. What determines the carrying capacity of an environment?
(A) Number of predator species
(B) Availability of resources
(C) Number of neighboring communities
(D) Speed of succession
Answer
(B) — Carrying capacity depends on how much food, water, space, and other resources are available.
3. Which survivorship curve is characterized by high infant mortality but survival of a few to adulthood?
(A) Type I
(B) Type II
(C) Type III
(D) Logistic
Answer
(C) — Type III shows many individuals dying early with only a few surviving to adulthood.
4. Which of the following is an example of a community-level interaction?
(A) Photosynthesis
(B) Cellular respiration
(C) Predation
(D) DNA replication
Answer
(C) — Predation occurs between species and is a community-level interaction.
5. What kind of growth produces a J-shaped curve?
(A) Logistic growth
(B) Declining growth
(C) Exponential growth
(D) Linear growth
Answer
(C) — Exponential growth produces a J-shaped curve when populations grow without limits.
6. Which species interaction benefits both species involved?
(A) Parasitism
(B) Competition
(C) Mutualism
(D) Predation
Answer
(C) — Mutualism benefits both species (+/+ interaction).
7. Which term refers to the number of different species in an ecosystem?
(A) Carrying capacity
(B) Biomass
(C) Species richness
(D) Population density
Answer
(C) — Species richness measures biodiversity in terms of species count.
8. What is the primary difference between primary and secondary succession?
(A) Primary succession occurs after disturbance with existing soil
(B) Secondary succession starts on bare rock
(C) Primary succession begins without soil
(D) Secondary succession lacks any organisms
Answer
(C) — Primary succession occurs where there is no soil, such as after lava flows or glacier retreat.
9. Which of the following best defines community ecology?
(A) Study of individual behavior
(B) Study of interactions between populations of different species
(C) Study of gene expression
(D) Study of organismal physiology
Answer
(B) — Community ecology examines how different species interact in the same area.
10. A density-independent factor affecting population size is:
(A) Disease
(B) Food competition
(C) Predation
(D) Hurricane
Answer
(D) — Natural disasters affect populations regardless of their density.
11. Which organism would likely be at the top of a trophic pyramid?
(A) Primary producer
(B) Herbivore
(C) Secondary consumer
(D) Apex predator
Answer
(D) — Apex predators are at the top, feeding on other consumers.
12. What does population dispersion describe?
(A) Birth and death rates
(B) Spatial arrangement of individuals
(C) Mutation frequency
(D) Species extinction rate
Answer
(B) — Dispersion describes how individuals are spaced within an area: uniform, clumped, or random.
13. Which of the following is most likely to reduce biodiversity?
(A) Habitat conservation
(B) Ecotourism
(C) Deforestation
(D) Predator-prey relationships
Answer
(C) — Deforestation destroys habitats, often reducing biodiversity.
14. Which of the following is a measure of ecosystem stability?
(A) Number of top predators
(B) Rate of energy transfer
(C) Resistance to disturbance
(D) Light penetration
Answer
(C) — Ecosystems that resist or recover from disturbances show higher stability.
15. A food chain always starts with:
(A) Decomposer
(B) Herbivore
(C) Primary consumer
(D) Producer
Answer
(D) — Producers (e.g., plants) convert energy into biomass and support the rest of the food chain.
16. What happens to energy as it moves up trophic levels?
(A) It increases
(B) It stays the same
(C) It decreases
(D) It cycles infinitely
Answer
(C) — Energy is lost as heat at each level, typically around 90% per step.
17. What is the role of a keystone species?
(A) Consume all prey species
(B) Control abiotic factors
(C) Maintain community structure
(D) Outcompete invasive species
Answer
(C) — Keystone species play a critical role in maintaining ecosystem balance.
18. Which of the following best explains why biodiversity is important to ecosystems?
(A) Increases human access
(B) Reduces habitat fragmentation
(C) Improves survival under changing conditions
(D) Enhances soil erosion
Answer
(C) — High biodiversity improves resilience to environmental changes.
19. Which organism is most likely to be a pioneer species?
(A) Oak tree
(B) Lichen
(C) Rabbit
(D) Snake
Answer
(B) — Lichens are often first colonizers in barren environments, such as rock surfaces.
20. Which of the following interactions is most likely to lead to coevolution?
(A) Commensalism
(B) Mutualism
(C) Abiotic stress
(D) Genetic drift
Answer
(B) — Mutualistic relationships often lead to reciprocal evolutionary changes between species.
21. What term describes species that arrive first during succession?
(A) Invasive species
(B) Indicator species
(C) Pioneer species
(D) Apex consumers
Answer
(C) — Pioneer species are the first to colonize disturbed or new environments.
22. Which is an example of a biotic factor that affects population size?
(A) Sunlight
(B) Temperature
(C) Predation
(D) pH level
Answer
(C) — Predation involves living organisms and influences population size.
23. Which is the best indicator of species evenness?
(A) Number of keystone species
(B) Relative abundance of species
(C) Total biomass
(D) Trophic level diversity
Answer
(B) — Evenness refers to how equally individuals are spread among species in a community.
24. Which of the following does not directly increase biodiversity?
(A) Habitat heterogeneity
(B) Moderate disturbance
(C) Climate stability
(D) Overharvesting
Answer
(D) — Overharvesting depletes populations and can lead to species loss.
25. What is the main consequence of biological magnification in food chains?
(A) Biomass decreases
(B) Oxygen increases
(C) Toxins accumulate at higher trophic levels
(D) Predators reproduce faster
Answer
(C) — Toxins like mercury become more concentrated in organisms higher up the food chain.
26. Which of the following best explains why population growth slows near carrying capacity?
(A) Predation increases linearly
(B) Birth rate exceeds death rate
(C) Resources become limited
(D) Immigration increases
Answer
(C) — As populations approach carrying capacity, competition for limited resources slows growth.
27. Which ecological concept states that two species cannot occupy the same niche indefinitely?
(A) Resource partitioning
(B) Competitive exclusion principle
(C) Keystone theory
(D) Intermediate disturbance hypothesis
Answer
(B) — The competitive exclusion principle states that one species will outcompete the other when niches overlap completely.
28. How does top-down control affect community structure?
(A) Primary producers regulate biodiversity
(B) Abiotic factors control trophic dynamics
(C) Predators regulate population sizes of lower trophic levels
(D) Keystone species promote mutualism
Answer
(C) — In top-down control, predators help regulate the abundance of prey, influencing community composition.
29. Which of the following would most likely cause a trophic cascade?
(A) Decrease in herbivore population
(B) Elimination of a top predator
(C) Increased plant growth
(D) Addition of decomposers
Answer
(B) — Removing top predators disrupts balance, allowing herbivore populations to rise, which in turn affects producers.
30. What makes biodiversity hotspots particularly important for conservation efforts?
(A) They have low species richness
(B) They contain large quantities of abiotic diversity
(C) They have high endemism and are under threat
(D) They are areas of high nutrient recycling
Answer
(C) — Biodiversity hotspots are regions with many endemic species and face significant threats from human activity.
31. Which of the following best explains why small, isolated populations are more vulnerable to extinction?
(A) They evolve rapidly
(B) They experience higher mutation rates
(C) They suffer from inbreeding and genetic drift
(D) They compete better with generalist species
Answer
(C) — Isolated populations face limited gene flow and are more affected by random genetic changes, increasing extinction risk.
32. In the context of population ecology, what does "r" represent in the exponential growth model?
(A) Number of species
(B) Reproductive rate per individual
(C) Carrying capacity
(D) Time interval
Answer
(B) — “r” is the per capita rate of increase, representing the difference between birth and death rates per individual.
33. What is the most likely outcome of repeated high disturbance in an ecosystem?
(A) Increased species evenness
(B) Reduced biodiversity
(C) Enhanced climax community development
(D) Increased reproductive success
Answer
(B) — Frequent intense disturbances can eliminate sensitive species and reduce overall biodiversity.
34. Which of the following species characteristics would make it a poor colonizer in a disturbed ecosystem?
(A) High fecundity
(B) Broad niche
(C) Long lifespan and late reproduction
(D) Rapid development
Answer
(C) — K-selected species with slow reproduction and long lifespans are less effective at colonizing new or disturbed habitats.
35. Which process explains how energy flows but nutrients cycle within ecosystems?
(A) Entropy theory
(B) Thermodynamic decay
(C) Trophic transfer efficiency
(D) Laws of thermodynamics
Answer
(D) — Energy flows in one direction due to entropy (2nd law of thermodynamics), while nutrients are recycled within the system.
36. Explain how population density can influence birth and death rates in a species.
Answer
As population density increases, competition for limited resources can raise death rates and lower birth rates due to stress, crowding, and food scarcity.
37. Describe the relationship between ecosystem complexity and stability.
Answer
More complex ecosystems with greater biodiversity tend to be more stable, as species can buffer each other’s loss and provide functional redundancy.
38. What is meant by “habitat fragmentation” and how does it affect biodiversity?
Answer
Habitat fragmentation divides ecosystems into smaller, isolated patches, reducing gene flow and increasing species vulnerability to extinction.
39. How does ecological succession contribute to long-term ecosystem development?
Answer
Succession gradually changes species composition, soil quality, and nutrient cycling, leading to more mature, biodiverse, and stable ecosystems over time.
40. Why are invasive species often so successful in new environments?
Answer
Invasive species often lack natural predators or competitors in new environments, allowing them to grow and spread rapidly.
41. Define the concept of a trophic level and give one example.
Answer
A trophic level is a step in a food chain representing energy flow. For example, herbivores are primary consumers on the second trophic level.
42. How do limiting factors control population size in ecosystems?
Answer
Limiting factors such as food, water, space, and predation keep populations from growing indefinitely by reducing reproduction or increasing mortality.
43. What is the role of decomposers in maintaining ecosystem health?
Answer
Decomposers break down dead organisms and recycle nutrients, supporting producers and keeping ecosystems functioning efficiently.
44. Explain the concept of “biotic potential” and how it contrasts with environmental resistance.
Answer
Biotic potential is the maximum growth rate of a species under ideal conditions, while environmental resistance includes limiting factors that slow growth.
45. What is the difference between generalist and specialist species?
Answer
Generalists can survive in a wide range of environments and diets, while specialists rely on narrow conditions and specific resources.
46. Describe how a change in one trophic level can affect an entire ecosystem.
Answer
Changes such as predator loss can alter prey populations and vegetation, cascading through the ecosystem and disrupting balance.
47. What is meant by ecosystem resilience?
Answer
Resilience is the ability of an ecosystem to recover after a disturbance and return to its original structure and function.
48. How do pioneer species modify their environment to enable other species to colonize?
Answer
Pioneer species alter the environment by breaking down rock, enriching soil with organic material, and reducing erosion, making it habitable for other species.
49. Why is genetic diversity important for population survival?
Answer
Genetic diversity provides the raw material for evolution and adaptation, making populations more resilient to disease and environmental changes.
50. How can human land-use changes negatively impact community structure?
Answer
Urbanization, deforestation, and agriculture can disrupt habitats, eliminate niches, and reduce biodiversity, weakening ecosystem functions.