201. Which statement best expresses Gause’s Competitive Exclusion Principle?
ⓐ. Two closely related species using the same limiting resource cannot coexist indefinitely.
ⓑ. All competing species eventually become mutualistic partners.
ⓒ. Competition can occur only when predators are absent.
ⓓ. Species with different food habits can never share a habitat.
Correct Answer: Two closely related species using the same limiting resource cannot coexist indefinitely.
Explanation: Gause’s principle states that complete ecological overlap for a limiting resource is unstable over the long term. When two very similar species depend on the same critical resource, one tends to outcompete the other.
202. Which condition is most important for competitive exclusion to occur?
ⓐ. The two species must occupy different habitats.
ⓑ. The two species must depend on the same limiting resource.
ⓒ. Both species must reproduce at exactly the same rate.
ⓓ. Predators must be absent from the ecosystem.
Correct Answer: The two species must depend on the same limiting resource.
Explanation: Competitive exclusion becomes most likely when species overlap strongly in resource use and that resource is limiting. Under such conditions, even a small competitive advantage can allow one species to displace the other over time. The issue is not identical reproduction rate or total absence of predators.
203. Which of the following best describes resource partitioning?
ⓐ. One species completely eliminates another from the habitat.
ⓑ. A predator restricts prey abundance and maintains diversity.
ⓒ. Two species avoid direct competition by using different resources or using the same resource differently.
ⓓ. One species benefits while the other remains unaffected.
Correct Answer: Two species avoid direct competition by using different resources or using the same resource differently.
Explanation: Resource partitioning allows similar species to coexist by reducing direct overlap in resource use. They may feed at different times, occupy different parts of the habitat, or use different foraging methods. This lowers the intensity of competition that would otherwise be expected.
204. Which statement best explains how closely related species may continue to coexist in nature despite competition?
ⓐ. They always evolve into parasites of one another.
ⓑ. They stop reproducing in the same season permanently.
ⓒ. They become completely unaffected by one another.
ⓓ. They may reduce overlap through resource partitioning.
Correct Answer: They may reduce overlap through resource partitioning.
Explanation: Coexistence can persist when species do not compete in exactly the same way for the same limiting resource. Differences in feeding site, timing, or method can reduce overlap enough for both to survive. This adjustment is called resource partitioning.
205. MacArthur’s warblers are a classic example of
ⓐ. predation maintaining species diversity
ⓑ. resource partitioning among similar species
ⓒ. brood parasitism with egg mimicry
ⓓ. amensalism in forest communities
Correct Answer: resource partitioning among similar species
Explanation: MacArthur’s warblers used different parts of the same tree and different foraging patterns, reducing direct competition. Although the species were similar, they did not exploit the habitat in exactly the same manner. This allowed them to coexist rather than exclude one another.
206. Which situation best represents resource partitioning?
ⓐ. Two bird species feed on the same insect at the same place and time.
ⓑ. One barnacle species completely displaces another from rocky shore.
ⓒ. A tick feeds on the blood of a mammal host.
ⓓ. Two lizard species live on the same tree, but one hunts near the trunk while the other forages on outer branches.
Correct Answer: Two lizard species live on the same tree, but one hunts near the trunk while the other forages on outer branches.
Explanation: Resource partitioning is seen when similar species use the environment differently enough to reduce direct competition. In this example, both lizards share the same tree but use different microhabitats for feeding. That difference lowers niche overlap.
207. Assertion: Competitive exclusion should not be treated as an absolute outcome in every natural habitat.
Reason: Species may coexist when they differ enough in resource use to reduce direct competition.
ⓐ. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
ⓑ. Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
ⓒ. Assertion is true, but Reason is false.
ⓓ. Assertion is false, but Reason is true.
Correct Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
Explanation: Competitive exclusion is an important principle, but natural communities often contain mechanisms that reduce complete overlap. Resource partitioning is one such mechanism and can allow similar species to share a habitat.
208. Which outcome is most likely when two species use exactly the same limiting resource for a long time without any niche differentiation?
ⓐ. Stable mutualism
ⓑ. Competitive exclusion
ⓒ. Commensalism
ⓓ. Resource partitioning
Correct Answer: Competitive exclusion
Explanation: If resource overlap remains complete and the resource is limiting, long-term coexistence becomes difficult. One species usually proves even slightly more efficient and gradually displaces the other. This is the essence of competitive exclusion.
209. Which statement best distinguishes competitive release from resource partitioning?
ⓐ. Competitive release occurs when overlap increases, whereas resource partitioning occurs when both species become extinct.
ⓑ. Competitive release follows removal of a competitor, whereas resource partitioning allows coexistence by reducing overlap.
ⓒ. Competitive release is a form of parasitism, whereas resource partitioning is a form of mutualism.
ⓓ. Competitive release involves shared feeding time, whereas resource partitioning involves identical resource use.
Correct Answer: Competitive release follows removal of a competitor, whereas resource partitioning allows coexistence by reducing overlap.
Explanation: Competitive release happens after the limiting effect of a competitor is removed, allowing a species to expand. Resource partitioning is different because both species remain present and avoid intense competition by using resources differently. One concept focuses on removal of competition, while the other focuses on reduction of overlap.
210. Fill in the blank in the most accurate way:
When similar species share a habitat by feeding in different places, at different times, or by different methods, they are showing ______.
ⓐ. competitive exclusion
ⓑ. predation pressure
ⓒ. brood parasitism
ⓓ. resource partitioning
Correct Answer: resource partitioning
Explanation: Different use of the same habitat lowers direct competition and allows species to persist together. The separation may be spatial, temporal, or behavioural. This pattern is called resource partitioning because the available resource space is effectively divided.
211. Which statement best defines parasitism as an ecological interaction?
ⓐ. Both species benefit by living closely together.
ⓑ. One species benefits and the other remains unaffected.
ⓒ. One species benefits while the other is harmed.
ⓓ. Both species are harmed because they share a resource.
Correct Answer: One species benefits while the other is harmed.
Explanation: Parasitism is an interaction in which the parasite gains food, shelter, or another advantage from the host. The host, however, suffers reduced fitness as a result of the association. This harm may appear as lowered survival, growth, or reproduction.
212. Which statement about host specificity in parasites is most accurate?
ⓐ. Many parasites are adapted to live in or on a particular host species.
ⓑ. Every parasite can live equally well on all available hosts.
ⓒ. Host specificity means the host is never harmed by the parasite.
ⓓ. Host specificity occurs only in plant parasites and not in animal parasites.
Correct Answer: Many parasites are adapted to live in or on a particular host species.
Explanation: Host specificity means that a parasite is often closely associated with a limited range of hosts, sometimes even a single host species. This happens because the parasite’s survival and reproduction depend on matching the host’s body conditions, defenses, and life cycle. Such specialization is common in parasitic relationships.
213. Which feature best distinguishes parasitism from predation?
ⓐ. In parasitism, both species benefit.
ⓑ. In parasitism, the host is never harmed.
ⓒ. In parasitism, the parasite always kills the host immediately.
ⓓ. In parasitism, the parasite usually exploits the host over a period of time instead of killing it at once.
Correct Answer: In parasitism, the parasite usually exploits the host over a period of time instead of killing it at once.
Explanation: Predators generally kill and consume prey, whereas parasites usually remain associated with the host for a longer duration. The parasite derives benefit continuously or repeatedly while the host remains alive, at least for some time. This long-term exploitation is a key feature of parasitism.
214. A parasite living on a host is most likely to reduce the host’s
ⓐ. reproductive fitness only and never survival
ⓑ. survival, growth, and reproduction
ⓒ. age distribution without affecting body condition
ⓓ. carrying capacity of every other species in the habitat
Correct Answer: survival, growth, and reproduction
Explanation: Parasites harm hosts in several ways, not just one. They may weaken the host, slow growth, reduce reproductive output, and in severe cases lower survival. Because these effects reduce overall fitness, parasitism can influence host population performance as well.
215. Which statement best explains why host-parasite relationships often show co-evolution?
ⓐ. Hosts evolve defenses, and parasites evolve ways to overcome those defenses.
ⓑ. Hosts and parasites always become mutualistic over time.
ⓒ. Parasites gradually stop depending on the host species.
ⓓ. Hosts lose all selective pressure once parasitism begins.
Correct Answer: Hosts evolve defenses, and parasites evolve ways to overcome those defenses.
Explanation: Co-evolution occurs when two interacting species exert selective pressure on each other over time. Hosts may evolve resistance mechanisms, while parasites evolve counter-adaptations that help them survive and reproduce successfully. This creates a continuing evolutionary interaction.
216. Which of the following situations is the best example of parasitism?
ⓐ. A bird feeds on insects disturbed by grazing cattle.
ⓑ. Two plants compete for the same mineral nutrients.
ⓒ. A wasp pollinates a flower while laying eggs.
ⓓ. A tapeworm absorbs nutrients from the intestine of its host.
Correct Answer: A tapeworm absorbs nutrients from the intestine of its host.
Explanation: A tapeworm benefits by obtaining nourishment from the host’s intestine, while the host is harmed by nutrient loss and physiological stress. This is a classic parasite-host relationship. The parasite gains directly from the host body rather than simply sharing space or resources.
217. Which statement about the effect of parasites on host populations is correct?
ⓐ. Parasites can lower host population density by reducing host fitness.
ⓑ. Parasites always increase the reproductive rate of the host population.
ⓒ. Parasites affect only individual hosts and never population-level patterns.
ⓓ. Parasites always kill the host before reproduction occurs.
Correct Answer: Parasites can lower host population density by reducing host fitness.
Explanation: When parasites reduce host survival or reproduction, the effect can extend beyond individuals to the whole population. Lower fitness in many hosts may reduce overall population density over time.
218. Assertion: Many parasites are restricted to particular hosts.
Reason: Successful parasitism often depends on adaptation to the host’s biology and defense mechanisms.
ⓐ. Assertion is false, but Reason is true.
ⓑ. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
ⓒ. Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
ⓓ. Assertion is true, but Reason is false.
Correct Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
Explanation: Host specificity is common because a parasite must function effectively within a particular biological environment. The host’s tissues, body chemistry, immune responses, and life cycle all create conditions the parasite must match. Adaptation to these conditions explains why many parasites are restricted to certain hosts.
219. A parasite weakens its host without killing it immediately and continues obtaining nourishment from it. This most directly shows that parasitism
ⓐ. benefits both parasite and host equally
ⓑ. always leads to competitive exclusion
ⓒ. involves prolonged exploitation of the host
ⓓ. is identical to predation in all respects
Correct Answer: involves prolonged exploitation of the host
Explanation: Many parasites depend on the host remaining alive long enough to continue providing food or shelter. This makes parasitism a sustained exploitative interaction rather than a rapid kill-and-consume event. The host is harmed, but often not destroyed at once.
220. Fill in the blank in the most accurate way:
Parasitism can reduce host survival, growth, reproduction, and even host ______.
ⓐ. camouflage
ⓑ. mutation rate
ⓒ. age at birth
ⓓ. population density
Correct Answer: population density
Explanation: When many individuals in a host population are negatively affected by parasites, the consequences can appear at the population level. Reduced survival and reproduction may lower the number of hosts present in the habitat. For this reason, parasitism is important not only for individual health but also for population dynamics.
