AP Biology: Seed Size and Disperser Trait Matching Practice Questions
Practice ecological reasoning with original AP Biology multiple-choice questions about compatibility between plant and animal traits. These items distinguish interaction from effective dispersal, explore how seed size and disperser morphology shape ecological networks, and test the evidence needed for causal conclusions.
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 plant produces fruits containing seeds wider than the gape of every small bird in a forest. Which animal trait would most directly permit whole-fruit ingestion?
Explanation. Morphological compatibility is a basic form of trait matching. A sufficiently wide gape can allow an animal to swallow a fruit that smaller-gaped birds cannot handle whole, although ingestion alone does not establish dispersal effectiveness.
2. Two rodents have similar body masses, but only one can open a very hard fruit and carry its seeds without crushing them. Which trait difference best explains the interaction?
Explanation. Body mass is only a proxy. Feeding structures and handling behavior can determine whether an animal accesses a fruit and whether seeds remain viable, so matching must be evaluated using traits relevant to the interaction.
3. Researchers predict plant-animal feeding links using fruit diameter and animal gape width. Which result would best support their trait-matching model?
Explanation. The model predicts a compatibility threshold: animals should be more likely to swallow fruits that fit within their gape. A higher frequency of observed links above that threshold supports the proposed mechanism.
4. Across several forests, large-seeded plants have more interactions with large-bodied animals. What is the most cautious conclusion?
Explanation. A correlation across communities supports a hypothesis but does not isolate the mechanism. Gape, handling, abundance, habitat use, and seed fate should be measured before attributing the pattern specifically to trait matching or effective dispersal.
5. Large-gaped birds disappear from a forest, and the remaining birds can only peck pulp from a large-fruited plant without moving its seeds. Which immediate effect is most likely?
Explanation. Loss of morphologically compatible dispersers can remove a seed-transport pathway. Pulp feeding may preserve a feeding interaction while failing to replace whole-seed movement, and evolutionary change is not immediate.
6. Two mammals swallow the same seed size, but passage through species A leaves more seeds viable than passage through species B. Which measurement best reveals this functional difference?
Explanation. Compatibility at ingestion is only one step. Testing germination and recruitment after gut passage shows whether handling physiology changes seed quality and therefore effective dispersal.
7. Which experiment most directly tests whether fruit size changes which birds can swallow fruits whole?
Explanation. Controlled fruit-size treatments connect a manipulated plant trait to a measured animal trait and feeding outcome. Holding other fruit characteristics as constant as possible strengthens the causal test.
8. A large-gaped bird eats both small and large fruits, while a small-gaped bird eats only small fruits. Which statement best describes the pattern?
Explanation. A lower size threshold can exclude a small-gaped species from large fruits, whereas a large-gaped species may still consume smaller fruits. Trait matching therefore need not create one-to-one specialization.
9. A warming trend causes a plant population to produce smaller fruits, but the local disperser community does not change. What data are most useful for predicting altered interaction links?
Explanation. Comparing the changed plant-trait distribution with relevant animal traits tests whether compatibility expands or contracts. Abundance and timing would also affect realized links, but unrelated measurements would not test the matching mechanism.
10. After a large disperser declines, small birds begin visiting its former partner plant but leave the seeds beneath the crown. What does this show?
Explanation. The network has rewired because new or stronger feeding links appear. However, deposition beneath the parent may not replace the former transport distance or deposition quality, so the ecological function can remain reduced.
11. Which response variable best evaluates whether seed-disperser trait matching improves plant recruitment?
Explanation. Recruitment integrates multiple steps: compatible handling, seed survival, movement, deposition quality, germination, and establishment. Interaction counts or body-size measurements alone cannot establish that outcome.
12. A bird's gape is wide enough to swallow a large fruit, but habitat fragmentation prevents the bird from reaching most fruiting trees. Which conclusion is best supported?
Explanation. A potential interaction requires both compatible traits and ecological opportunity. Fragmentation can reduce encounter rates even when morphology permits fruit handling, so realized networks reflect traits, abundance, timing, and space.
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FAQ
What is seed-disperser trait matching?
It is the compatibility between plant traits, such as fruit or seed size and hardness, and disperser traits, such as gape width, feeding structures, behavior, and gut physiology.
Does a feeding interaction prove effective seed dispersal?
No. Effective dispersal also depends on whether seeds remain viable, move away from the parent, reach suitable sites, germinate, and establish.
Why is body size not enough to predict dispersal function?
Body size can correlate with useful traits, but gape, handling behavior, movement, abundance, gut effects, habitat use, and spatial overlap more directly determine many dispersal outcomes.