IB Biology Quiz: Understand Ecological Niches
20 questions · exam conditions
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Understand Ecological NichesQuestion 1 of 20

A sudden blight eliminates a species of tree that provided the main food source for a specialist insect species. In the absence of this food, the insect begins to feed on a less nutritious, secondary plant species that it previously avoided. How can this change in feeding behaviour be described in terms of ecological niches?

An expansion of the realized niche due to a decrease in resource availability.
A contraction of the fundamental niche due to the loss of a primary resource.
A shift in the realized niche driven by a change in interspecific competition.
A shift in the realized niche towards the edge of the fundamental niche.
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IB Biology Quiz

IB Biology Quiz: Understand Ecological Niches

Practice Understand Ecological Niches in IB Biology with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Understand Ecological Niches, giving you a quick way to practice the rules, question types, and explanations that matter most for IB Biology.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

A sudden blight eliminates a species of tree that provided the main food source for a specialist insect species. In the absence of this food, the insect begins to feed on a less nutritious, secondary plant species that it previously avoided. How can this change in feeding behaviour be described in terms of ecological niches?

  1. An expansion of the realized niche due to a decrease in resource availability.
  2. A contraction of the fundamental niche due to the loss of a primary resource.
  3. A shift in the realized niche driven by a change in interspecific competition.
  4. A shift in the realized niche towards the edge of the fundamental niche. (correct answer)
Explanation: The correct answer is D. The fundamental niche includes all potential food sources, even less preferred ones. The realized niche was previously focused on the primary food source. The loss of this resource forces the species to utilize other parts of its fundamental niche that were previously unoccupied. This is best described as a shift of the realized niche towards the physiological limits, or edge, of its fundamental niche. It is not an expansion (A), as no new capability is gained. The fundamental niche itself does not contract (B). The shift is driven by resource loss, not a change in competition (C).

Question 2

An invasive plant species is introduced into a grassland ecosystem. It is a highly effective competitor for soil nitrogen, a key limiting resource for native plant species. What is the most probable immediate effect on the native plant species that also rely on soil nitrogen?

  1. Their fundamental niches will contract.
  2. Their realized niches will contract. (correct answer)
  3. Their fundamental niches will expand.
  4. Their realized niches will expand.
Explanation: The correct answer is B. The introduction of a superior competitor increases interspecific competition. This pressure will restrict the ability of the native species to access resources and occupy space, causing their realized niches (the conditions they actually live in) to contract. The fundamental niche (A, C), which is the potential range of conditions based on physiology, does not change in the short term. Expansion of the realized niche (D) would occur if a competitor were removed, not added.

Question 3

In a rocky intertidal zone, two species of limpets, Species A and Species B, graze on algae. Species A can tolerate greater exposure to air and desiccation, while Species B is a more efficient grazer and competitor in areas that remain moist. In areas where they coexist, Species A is found only in the upper, drier zone. What does this distribution suggest?

  1. The fundamental niche of Species A is smaller than its realized niche.
  2. The realized niche of Species A is restricted by interspecific competition. (correct answer)
  3. Species B has a wider fundamental niche than Species A regarding moisture.
  4. Competitive exclusion has failed, leading to a hybrid species.
Explanation: The correct answer is B. Species A can physiologically tolerate lower zones (implied by its competition with B there), but is outcompeted by Species B. Therefore, its actual distribution (realized niche) is restricted to the upper zone by this biotic interaction. The fundamental niche is always greater than or equal to the realized niche (making A incorrect). We cannot conclude anything definitive about the relative widths of their fundamental niches from the information given (C). There is no information to suggest hybridization (D).

Question 4

The concept of an ecological niche is often described as an 'n-dimensional hypervolume', where 'n' is the number of environmental factors important to a species' survival. Which of the following could not be considered a dimension of a species' fundamental niche?

  1. The range of temperatures in which the species can reproduce.
  2. The intensity of competition from a sympatric species. (correct answer)
  3. The minimum soil moisture level required for seed germination.
  4. The pH range of water that the species can tolerate.
Explanation: The correct answer is B. The fundamental niche is defined by a species' physiological tolerances and resource requirements, independent of biotic interactions. Therefore, abiotic factors like temperature (A), soil moisture (C), and pH (D) are all valid dimensions. In contrast, the intensity of competition is a biotic factor that determines the size and shape of the realized niche by restricting access to parts of the fundamental niche.

Question 5

Two species of desert ants compete for seeds. Where they occur separately (allopatry), both species forage during the cool hours of the early morning. Where they occur together (sympatry), one species continues to forage in the early morning, while the other has shifted to foraging during the hotter, midday period. This shift in foraging time in the sympatric population is an example of:

  1. competitive exclusion leading to local extinction.
  2. the competitive exclusion principle being violated.
  3. niche partitioning allowing for species coexistence. (correct answer)
  4. an expansion of the fundamental niches of both species.
Explanation: The correct answer is C. The two species are avoiding direct competition by using the same resource (seeds) at different times. This is a classic example of temporal niche partitioning, an outcome that allows competitors to coexist rather than one excluding the other. Competitive exclusion (A) is what is being avoided. The principle is not violated (B); rather, this is a common result of the selective pressures it describes. The fundamental niches are not expanding (D); instead, the realized niche of one species has shifted within its fundamental niche.

Question 6

A species is described as a 'specialist'. What does this imply about its ecological niche and its potential response to environmental change?

  1. It has a narrow fundamental niche and is vulnerable to changes in its key resource. (correct answer)
  2. It has a broad fundamental niche, allowing it to adapt easily to new conditions.
  3. It experiences high levels of interspecific competition across its entire range.
  4. Its realized niche is significantly larger than its fundamental niche.
Explanation: The correct answer is A. A specialist species has a narrow fundamental niche, meaning it has very specific requirements for food, habitat, or other abiotic factors. This specialization makes it highly efficient in a stable environment but very vulnerable if that specific environment or resource changes. A broad niche is characteristic of a 'generalist' (B). Specialization often evolves to reduce, not increase, interspecific competition (C). The realized niche can never be larger than the fundamental niche (D).

Question 7

If a keystone predator is removed from a community, a prey species that was previously controlled by predation may become a dominant competitor. How would this event affect the realized niches of other species that compete with the newly dominant species?

  1. Their realized niches would likely expand due to the absence of the predator.
  2. Their realized niches would likely contract due to increased interspecific competition. (correct answer)
  3. Their fundamental niches would contract as they are outcompeted for resources.
  4. Their fundamental niches and realized niches would both expand equally.
Explanation: The correct answer is B. The removal of the keystone predator releases one species from predatory control, allowing its population to grow and become a superior competitor. This increase in competitive pressure on other species will restrict their access to resources and habitats, causing their realized niches to contract. The predator's absence does not directly benefit them (A). Fundamental niches are defined by physiology and do not change in response to short-term ecological shifts (C, D).

Question 8

Which statement most accurately distinguishes between a species' habitat and its niche?

  1. A habitat is the physical place where an organism lives, while a niche is the role it plays in its ecosystem. (correct answer)
  2. A niche is the geographical range of an organism, while a habitat is the specific food it consumes.
  3. A habitat describes biotic interactions, while a niche describes the abiotic conditions an organism tolerates.
  4. A niche and a habitat are synonymous terms for the environment in which an organism is found.
Explanation: The correct answer is A. This is the classic distinction. A habitat is the 'address' of an organism (e.g., a coral reef, a temperate forest floor), whereas a niche is its 'profession' or functional role, which includes its trophic position, resource use, and interactions with other species within that habitat. B reverses the definitions. C is incorrect as a niche encompasses both biotic and abiotic factors. D is incorrect as the terms have distinct meanings.

Question 9

A scientist observes that when two species of fish are in the same pond, they both exhibit stunted growth compared to when they are in separate ponds with identical resources. Which statement is the most valid conclusion?

  1. The fundamental niche of each species is reduced by the presence of the other.
  2. One species will inevitably drive the other to extinction from the pond.
  3. The two species occupy completely separate realized niches within the pond.
  4. The two species are engaged in interspecific competition that reduces their fitness. (correct answer)
Explanation: The correct answer is B. Stunted growth is a measure of reduced fitness. Since this occurs when they are together but not when they are apart, it strongly indicates that interspecific competition is occurring. The fundamental niche is a physiological property and is not reduced by a competitor (A). If their realized niches were completely separate, they would not compete and their growth would not be affected (C). While competition is occurring, we cannot conclude that extinction is inevitable; they might coexist at lower population densities (D).

Question 10

Two similar species of coral are found on a reef. Species P thrives in high-light, shallow water, while Species Q excels in low-light, deeper water. In the zone where their distributions overlap, the growth rate of both species is significantly reduced compared to their growth rates in their preferred zones. What can be deduced from this observation?

  1. Competitive exclusion will inevitably lead to the extinction of one species.
  2. The fundamental niches of the two species are completely different.
  3. There is a zone of niche overlap where interspecific competition occurs. (correct answer)
  4. The two species have formed a mutualistic relationship in the overlap zone.
Explanation: The correct answer is C. The reduced growth rate for both species in the overlap zone is a classic sign of interspecific competition. This indicates that their niches overlap in this intermediate zone and they are negatively impacting each other's fitness. While competition occurs, it may not lead to complete exclusion (A) if they each have a refuge in their preferred zones. Their niches are not completely different, otherwise they would not interact negatively (B). A mutualistic relationship would result in increased, not decreased, growth rates (D).

Question 11

A disease eliminates a species of grass that was the dominant competitor in a meadow. Following its removal, a smaller, less competitive species of wildflower, which was previously rare, becomes abundant and widespread throughout the meadow. This change for the wildflower represents:

  1. an expansion of its realized niche due to competitive release. (correct answer)
  2. an expansion of its fundamental niche due to a change in abiotic factors.
  3. a contraction of its realized niche due to the loss of a food source.
  4. a contraction of its fundamental niche due to disease pressure.
Explanation: The correct answer is A. The removal of a superior competitor is termed 'competitive release'. This allows the previously suppressed species to access resources and occupy habitats from which it was formerly excluded. This is an expansion of its realized niche, which grows to more fully occupy its pre-existing fundamental niche. The fundamental niche itself (B, D) does not change. The niche expands, not contracts (C).

Question 12

A species of barnacle can physiologically tolerate a wide range of water depths and temperatures when raised in a laboratory aquarium free from other species. However, in its natural marine environment, it is only found within a narrow tidal zone, primarily due to the presence of a more aggressive, competing barnacle species in deeper water. The narrow tidal zone where the barnacle is found in nature represents its:

  1. fundamental niche, because it is where the species survives.
  2. realized niche, because its distribution is restricted by biotic interactions. (correct answer)
  3. ecological equivalent, because it coexists with a competitor.
  4. resource partition, because it occupies a specific physical space.
Explanation: The correct answer is B. The realized niche is the actual range of conditions and resources an organism uses, which is often restricted by biotic interactions like competition. The fundamental niche is the potential range without such restrictions, described by its laboratory tolerance. 'Ecological equivalent' refers to species with similar niches in different geographical locations. 'Resource partition' is a mechanism to avoid competition, not a description of the niche itself.

Question 13

Two species of finch live on the same island. Species X has a slightly larger beak and eats slightly larger seeds than Species Y. An environmental change causes the extinction of plants producing medium-sized seeds, leaving only very small and very large seeds. Which ecological concept describes the most likely evolutionary response in these finch species over many generations?

  1. Competitive exclusion, as one species will eliminate the other.
  2. Character displacement, as beak sizes will diverge further to specialize on available seeds. (correct answer)
  3. Niche expansion, as both species will attempt to eat both remaining seed sizes.
  4. Mutualism, as the species will cooperate to access the new food sources.
Explanation: The correct answer is B. Character displacement is an evolutionary divergence in characteristics (like beak size) that occurs when two competing species co-occur. The pressure to reduce competition for the remaining food sources would likely select for even larger beaks in Species X (to specialize on large seeds) and smaller beaks in Species Y (to specialize on small seeds), causing their traits to diverge. Competitive exclusion (A) is a possible outcome, but character displacement is the specific evolutionary response described. Niche expansion (C) is unlikely as specialization would be favored.

Question 14

According to the competitive exclusion principle, what is the most likely long-term outcome when two different species are forced to occupy the exact same niche within a stable, unchanging ecosystem?

  1. One species will be eliminated from the ecosystem due to resource competition. (correct answer)
  2. The two species will evolve to form a stable, mutually beneficial relationship.
  3. Both species will coexist, but their population sizes will be significantly lower.
  4. The species will engage in temporal resource partitioning, becoming active at different times of day.
Explanation: The correct answer is A. The competitive exclusion principle states that two species competing for the same limiting resources cannot coexist indefinitely in the same place; the species with even a slight competitive advantage will eventually drive the other to local extinction. Coexistence (C) is not predicted under these strict conditions. Mutualism (B) and partitioning (D) are ways to avoid or evolve out of direct niche overlap, but the principle itself predicts exclusion if the niche overlap is complete.

Question 15

The competitive exclusion principle is most likely to apply and result in the elimination of one species when:

  1. the two competing species are distantly related.
  2. the ecosystem's resources are fluctuating and unpredictable.
  3. a key resource for both species is stable and limited in supply. (correct answer)
  4. the two species have a high degree of niche differentiation.
Explanation: The correct answer is C. Competitive exclusion operates most strongly when there is intense, constant competition for a resource that is in short supply (i.e., it is limiting). A stable and limited resource prevents the weaker competitor from finding refuge in times or places of temporary abundance. Fluctuating resources (B) can allow for coexistence. High niche differentiation (D) is the opposite of the condition for exclusion; it facilitates coexistence. The relatedness of species (A) is less important than the degree of niche overlap.

Question 16

In many ecosystems, different species of predators (e.g., lions and hyenas) often prey on the same species (e.g., wildebeest). This sharing of a food resource indicates that:

  1. their fundamental niches are identical.
  2. competitive exclusion does not apply to predators.
  3. they cannot be considered competitors.
  4. there is an overlap in one dimension of their niches. (correct answer)
Explanation: The correct answer is B. A niche is multi-dimensional. Sharing a food source means their niches overlap in the 'food resource' dimension. However, they may differ in other dimensions, such as hunting time (temporal), specific hunting locations (spatial), or preference for other prey, which allows them to coexist. Their fundamental niches are unlikely to be identical in all dimensions (A). They are competitors for that shared resource (C). Competitive exclusion does apply to predators, but coexistence is possible if niche overlap is not complete (D).

Question 17

Two species of insect larvae live on the same host plant. Species A feeds on the leaves, while Species B feeds on the roots. Which concept does this best illustrate?

  1. The competitive exclusion principle in action.
  2. Resource partitioning reducing interspecific competition. (correct answer)
  3. Identical fundamental niches leading to coexistence.
  4. A predator-prey relationship between the two larvae.
Explanation: The correct answer is B. The two species are utilizing different parts of the same resource (the host plant). This is a form of resource partitioning that allows them to coexist by minimizing direct competition for food. It is an example of competition being avoided, not competitive exclusion in action (A). Their fundamental niches are clearly not identical, as they are specialized on different parts of the plant (C). There is no information suggesting a predator-prey relationship (D).

Question 18

Which of the following scenarios is the clearest example of temporal niche partitioning?

  1. Two species of birds feeding on insects in different parts of the same tree.
  2. A hawk species that hunts during the day and an owl species that hunts in the same area at night. (correct answer)
  3. Two species of squirrels, one of which can digest acorns and the other only hickory nuts.
  4. A species of fish that lives in the shallow water of a lake and another that lives in the deep water.
Explanation: The correct answer is B. Temporal partitioning involves using the same resource at different times. The hawk and owl hunt in the same area (sharing a spatial niche) but at different times (day vs. night). Feeding in different parts of a tree (A) is spatial partitioning. Eating different foods (C) is resource partitioning. Living at different depths (D) is also a form of spatial partitioning.

Question 19

A field experiment is designed to determine the fundamental niche of a specific plant species, Plantago maritima. Which experimental procedure would be most effective for this purpose?

  1. Mapping the exact current distribution of Plantago maritima in the field.
  2. Growing Plantago maritima in a greenhouse across a range of abiotic conditions. (correct answer)
  3. Removing the primary herbivore of Plantago maritima from a series of plots.
  4. Removing all other competing plant species from a series of plots where Plantago maritima is present.
Explanation: The correct answer is B. The fundamental niche is defined by the physiological tolerance of a species to abiotic factors, in the absence of biotic interactions like competition and predation. Growing the plant in a controlled greenhouse environment without competitors allows researchers to determine the full range of physical conditions (temperature, moisture, pH, etc.) under which it can survive and reproduce. Mapping its current distribution (A) determines the realized niche. Removing competitors (D) or herbivores (C) would measure the effect of those specific interactions on the realized niche, but not the full range of abiotic tolerance.

Question 20

What is the key difference between the conditions that lead to competitive exclusion and the conditions that lead to resource partitioning?

  1. Competitive exclusion involves abiotic factors, while resource partitioning involves biotic factors.
  2. Competitive exclusion occurs when resources are abundant, while resource partitioning occurs when they are scarce.
  3. Competitive exclusion results in increased biodiversity, while resource partitioning results in decreased biodiversity.
  4. Competitive exclusion occurs when niche overlap is high, while partitioning is a response that reduces niche overlap. (correct answer)
Explanation: The correct answer is B. Competitive exclusion is the outcome predicted when niche overlap between two species is nearly complete, and competition is intense. Resource partitioning is an evolutionary or behavioural response that allows species to coexist by differentiating their niches and thus reducing the degree of overlap and competition. Both processes involve biotic and abiotic factors (A). Partitioning maintains or increases biodiversity, while exclusion reduces it (C). Both processes are driven by resource scarcity, not abundance (D).