AP Biology: Disease Ecology and Community Effects Practice Questions
Practice disease-ecology reasoning with original AP Biology multiple-choice questions. These items focus on transmission patterns, host-pathogen interactions, community change, experimental evidence, and cautious interpretation of ecological data.
Free original practice questions for study purposes. Open Exam Prep is an independent study resource and is not affiliated with, endorsed by, or sponsored by the makers of AP Exams.
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1. A directly transmitted pathogen spreads when infected and susceptible hosts make close contact. Which change would most likely increase transmission if all other factors remain similar?
Explanation. For a density-dependent contact process, more hosts per unit area can increase encounter rates between infected and susceptible individuals. Taxonomic labels do not alter transmission, and removing susceptible hosts would reduce opportunities for new infections.
2. Researchers find that the proportion of infected hosts stays similar across populations of very different densities because each host maintains about the same number of social partners. Which transmission pattern best fits this observation?
Explanation. When the number of relevant contacts per host changes little with population density, transmission can depend more on the fraction of contacts that are infectious than on the total density of hosts. The pattern alone does not establish the other claims.
3. A mammal species carries a pathogen for long periods with few effects, while biting insects transfer the pathogen from that mammal to another host species. What roles do the mammal and insect most directly play?
Explanation. A reservoir host can maintain a pathogen over time, while a vector carries it between hosts. These ecological roles describe pathogen persistence and movement rather than trophic level or abiotic status.
4. A pathogen sharply reduces an abundant grazing snail population in a marsh. Algal biomass then increases. Which explanation is best supported by this sequence?
Explanation. If snails consume algae, a pathogen-driven decline in snails can reduce grazing pressure and allow algal biomass to rise. This is an indirect community effect mediated through a host population.
5. Which study would best test whether host species richness changes pathogen transmission in a plant community?
Explanation. Replicated richness treatments with similar total density isolate species richness more effectively than designs that confound richness with host abundance. Standardized exposure and measured transmission provide evidence relevant to the hypothesis.
6. Adding a poorly competent host species reduces the fraction of vector bites received by a highly competent host. If vector abundance does not change, what outcome is most plausible?
Explanation. A poorly competent host may divert vector contacts away from a host that efficiently transmits the pathogen, potentially lowering transmission. This dilution-like outcome depends on the species and interaction details rather than following from richness alone.
7. In another community, adding a host species increases food available to a vector, causing the vector population to grow. Pathogen prevalence then rises. Why does this not contradict evidence that diversity reduced transmission elsewhere?
Explanation. Community composition affects several mechanisms. Added species can dilute infectious contacts in one system but increase vector abundance or competent-host density in another, so the direction of the effect must be tested rather than assumed.
8. A field survey shows that warmer years are associated with both more vectors and greater pathogen prevalence. Which conclusion is most scientifically appropriate?
Explanation. A correlation can motivate a causal hypothesis, but other variables may change with temperature. Controlled studies, mechanistic measurements, or analyses that address confounding factors are needed for a stronger causal conclusion.
9. A pathogen reduces the survival of the competitively dominant plant in a grassland. Several previously rare plant species increase in abundance. What is the most direct community-level interpretation?
Explanation. By disproportionately reducing a dominant competitor, the pathogen can release other plant species from competition and change relative abundance. Competition may still occur, and the species do not become ecologically identical.
10. Why can a pathogen persist in a metapopulation even when infection frequently disappears from individual habitat patches?
Explanation. Regional persistence can result from asynchronous local dynamics and movement among patches. Infection may vanish locally but be reintroduced from another occupied patch before it disappears from the full network.
11. Two host populations receive equal pathogen exposure. Population A has low genetic variation at immune-related loci, while Population B has high variation. Which prediction is reasonable but not guaranteed?
Explanation. Greater immune-related variation can create heterogeneous host responses, which may limit uniform susceptibility. The effect is probabilistic because environment, pathogen traits, behavior, and other genes also influence outcomes.
12. After a pathogen enters a food web, researchers observe declines in one predator, increases in its prey, and decreases in the prey's food resource. What additional evidence would best support a pathogen-triggered trophic cascade?
Explanation. A trophic-cascade claim is stronger when replicated data connect pathogen effects on the predator to the predicted downstream changes in prey and resources. Temporal order alone is suggestive but may not rule out alternative causes.
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FAQ
What does disease ecology study?
Disease ecology examines how hosts, pathogens, vectors, environments, and ecological communities interact to shape transmission and population or community outcomes.
Does greater biodiversity always reduce disease transmission?
No. Added species can alter host competence, contact rates, reservoir abundance, or vector populations. The direction and size of the effect depend on community composition and mechanism.
How can a pathogen affect species it does not infect?
By changing the abundance or behavior of an infected host, a pathogen can indirectly alter competition, predation, grazing, or resource availability throughout a community.