AP Biology: Competitive Exclusion and Resource Partitioning Practice Questions
Practice competitive exclusion and resource partitioning with original AP Biology multiple-choice questions. These items connect niche overlap to interspecific competition, coexistence mechanisms, realized niches, character displacement, and experimental evidence.
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1. Two species depend on the same limiting resource in the same habitat and use that resource in nearly identical ways. If the environment remains stable, which outcome is predicted by the competitive exclusion principle?
Explanation. Species with effectively identical niches cannot usually coexist indefinitely when the same resource limits both. A competitive advantage can drive local exclusion unless niche differences or environmental changes permit coexistence.
2. Several insect-eating bird species occupy the same forest but forage in different parts of the trees. Which process most directly reduces competition among them?
Explanation. Using different portions of the habitat divides the available food resource spatially. This resource partitioning reduces niche overlap and can promote coexistence.
3. Two nocturnal rodent species eat the same seeds, but one feeds mainly just after sunset and the other mainly before sunrise. This pattern is an example of what?
Explanation. The species divide access to a shared resource by feeding at different times. Temporal partitioning can reduce direct encounters and competition.
4. A plant species grows across both dry and moist soils when cultured alone, but in a natural community it occurs only on dry soil because a competitor dominates moist soil. The dry-soil distribution in the community represents what?
Explanation. The realized niche is the portion of environmental conditions a species actually occupies after biotic interactions such as competition restrict its broader fundamental niche.
5. Researchers remove species B from half of several replicated ponds. Species A expands into shallow water only where B was removed. Which conclusion is best supported?
Explanation. Species A can use shallow water when B is absent, so competition from B likely prevented A from occupying part of its fundamental niche under normal conditions.
6. Closely related seed-eating species have more different beak sizes where they coexist than where each occurs alone. Which explanation best fits this pattern?
Explanation. Character displacement is greater trait divergence where competitors coexist. Divergent beak sizes can reduce overlap in food use and therefore reduce interspecific competition.
7. Which experimental design would best test whether two algal species compete for phosphate?
Explanation. Monocultures establish each species' performance without the competitor, mixed cultures reveal interaction effects, and controlled replicated phosphate treatments test whether the effect depends on the proposed limiting resource.
8. Two competing protist species coexist when supplied with two food particles because each species is more efficient at using a different particle type. What most directly explains their coexistence?
Explanation. A trade-off in resource-use efficiency creates niche differences. Each species is limited differently and can recover when the resource it uses best is relatively available.
9. A food analysis shows that species X and Y have strongly overlapping diets. Why is this result alone insufficient to demonstrate competitive exclusion?
Explanation. Competition depends on a shared resource being limiting, and exclusion depends on the full ecological context. Spatial, temporal, or other resource differences can still permit coexistence.
10. A drought makes the single water source used by two desert annuals much scarcer. If their water-use niches strongly overlap, what is the most likely immediate ecological effect?
Explanation. As a shared limiting resource becomes scarcer, each species' use leaves less available for the other. This strengthens the potential for interspecific competition.
11. Species P is a better competitor in nutrient-rich patches, while species Q survives better in nutrient-poor patches. A landscape containing both patch types can support both species. Which principle does this illustrate?
Explanation. Different patch conditions favor different competitors. Spatial heterogeneity therefore prevents one species from having the same advantage everywhere and can maintain regional coexistence.
12. After two lizard species begin living on the same island, one population increasingly uses low branches while the other uses high branches. Which observation would most strongly support competition as the cause of this partitioning?
Explanation. Broader, overlapping habitat use in allopatry but narrower, separated use in sympatry supports the hypothesis that interaction between the species drives niche partitioning.
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FAQ
What is the competitive exclusion principle?
Species that depend on the same limiting resource in effectively identical ways cannot usually coexist indefinitely in a stable environment; one may be locally excluded unless niche use changes.
How does resource partitioning promote coexistence?
Species divide resources by location, time, size, or type, which reduces niche overlap and weakens direct competition.
What evidence distinguishes competition from simple niche overlap?
Controlled removal, addition, or mixed-culture experiments that compare performance with and without a competitor provide stronger causal evidence than overlap alone.