Successions and Ecosystems Reading Answers

Nov 10, 2025

Successions and Ecosystems Reading Answers is an IELTS Reading Answer that contains 14 questions and needs to be completed within 20 minutes. The reading passage has nine paragraphs labelled a-i. Which paragraph contains the following information? Do the following statements agree with the information given in the reading passage? and choose the correct letter, a, b, c, or d.

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Successions and Ecosystems Reading Answers

Topic:

Succession and Ecosystems

A.Ecologists use the term “succession” to refer to the changes that happen in plant communities and ecosystems over time. In the early twentieth century, the American ecologist Frederic Clements pointed out that a succession of plant communities would develop after a disturbance such as a volcanic eruption, heavy flood, or forest fire. An abandoned field, for instance, will be invaded successively by herbaceous plants, shrubs, and trees, eventually becoming a forest.

B.The first community in a succession is called a pioneer community, while the established community at the end of a succession is called a climax community. Pioneer and successional plant communities are said to change over periods of 1 to 500 years. These changes—in plant numbers and the mix of species are cumulative. Climax communities themselves change but over periods of time greater than about 500 years. The final stage of a succession is not predictable or of uniform composition. There is usually a good deal of turnover in species composition, even in a mature community. The nature of the climax community is influenced by the same factors that influence succession. Nevertheless, mature natural environments are usually in equilibrium. They change relatively little through time unless the environment itself changes. Clements and other early ecologists saw an almost lawlike regularity in the order of succession, but that has not been substantiated. A general trend can be recognized, but the details are usually unpredictable. Succession is influenced by many factors: the nature of the soil, exposure to sun and wind, regularity of precipitation, chance colonizations, and many other arbitrary processes.

C.For Clements, the climax community was a "superorganism," an organic entity. Even some authors who accepted the climax community concept rejected Clements' characterization of it as a superorganism, and it is indeed a misleading metaphor. An ant colony may be legitimately called a superorganism because its communication system is so highly organized that the colony always works as a whole and appropriately according to the circumstances. But there is no evidence for such an interacting communicative network in a climax plant formation. Many authors prefer the term "association" to the term "community" in order to stress the looseness of the interaction.

D.Even less fortunate was the extension of this type of thinking to include animals as well as plants. This resulted in the "biome," a combination of coexisting flora and fauna. Though it is true that many animals are strictly associated with certain plants, it is misleading to speak of a "spruce-moose biome," for example, because there is no internal cohesion to their association as it would be with an organism. The spruce community is not substantially affected by either the presence or absence of moose. Indeed, there are vast areas of spruce forest without moose. The opposition to the Clementsian concept of plant ecology was initiated by Herbert Gleason, soon joined by various other ecologists. Their major point was that the distribution of a given species was controlled by the habitat requirements of that species and that, therefore, the vegetation types were a simple consequence of the ecologies of individual plant species.

E.With "climax," "biome," "superorganism," and various other technical terms for the association of animals and plants at a given locality being criticized, the term"ecosystem" was more and more widely adopted for the whole system of associated organisms together with the physical factors of their environment. Eventually, the energy-transforming role of such a system was emphasized. An ecologist is concerned primarily with the quantities of matter and energy that pass through a given ecosystem, and with the rates at which they do so. Today one speaks of the ecosystem when referring to a local association of animals and plants, usually without paying much attention to these energy aspects.

F.At one time, ecologists believed that species diversity made ecosystems stable. They believed that the greater the diversity the more stable the ecosystem. Support for this idea came from the observation that long-lasting climax communities usually have more complex food webs and more species diversity than pioneer communities. Ecologists concluded that the apparent stability of climax ecosystems depended on their complexity. To take an extreme example, farmlands dominated by a single crop are so unstable that one year of bad weather or the invasion of a single pest can destroy the entire crop. In contrast, a complex climax community, such as a temperate forest, will tolerate considerable damage from weather to pests.

G.The question of ecosystem stability is complicated, however. Stability can be defined as simply lack of change. In that case, the climax community would be considered the most stable, since, by definition, it changes the least over time. Alternatively, stability can be defined as the speed with which an ecosystem returns to a particular form following a major disturbance, such as a fire. This kind of stability is also called resilience. In that case, climax communities would be the most fragile and the least stable, since they can require hundreds of years to return to the climax state.

H.Even the kind of stability which is defined as simple lack of change is not always associated with maximum diversity. At least in temperate zones, maximum diversity is often found in mid-successional stages, not in the climax community. Once a redwood forest matures, for example, the kinds of species and the number of individuals growing on the forest floor are reduced. In general, diversity, by itself, does not ensure stability. Mathematical models of ecosystems likewise suggest that diversity does not guarantee ecosystem stability—just the opposite, in fact.

I.Many ecologists now think that the relative long-term stability of climax communities comes not from diversity but from the “patchiness” of the environment, an environment that varies from place to place supports more kinds of organisms than an environment that is uniform. A local population that goes extinct is quickly replaced by immigrants from an adjacent community. Even if the new population is of a different species, it can approximately fill the niche vacated by the extinct population and keep the food web intact.

QUESTIONS 15-20

THE READING PASSAGE HAS NINE PARAGRAPHS LABELLED A-I. WHICH PARAGRAPH CONTAINS THE FOLLOWING INFORMATION? WRITE THE CORRECT LETTER A-I IN BOXES 15-20 ON YOUR ANSWER SHEET.

NB You MAY USE ANY LETTER MORE THAN ONCE.

15. An opposition to the idea of plants and animals being associated with "superorganisms"

Answer: D

Supporting statement: The opposition to the Clementsian concept of plant ecology was initiated by Herbert Gleason... Their major point was that the distribution of a given species was controlled by the habitat requirements of that species

Keywords: Clementsian concept, species

Keyword Location: Para D, Lines 7-9

Explanation: This paragraph details the opposition, led by Gleason, to Clements' ideas, which included the superorganism metaphor.

16. Examples of various ecosystems which demonstrate that the degree of species diversity results in a stable ecosystem,

Answer: F

Supporting statement: To take an extreme example, farmlands dominated by a single crop are so unstable... In contrast, a complex climax community, such as a temperate forest, will tolerate considerable damage...

Keywords: farmlands dominated, temperate forest

Keyword Location: Para F, Lines 6-8

Explanation: This paragraph uses the contrast between unstable, low-diversity farmlands and stable, high-diversity temperate forests to support the initial belief about diversity and stability.

17. A discussion of random processes affecting specific details of successions.

Answer: B

Supporting statement: A general trend can be recognized, but the details are usually unpredictable. Succession is influenced by many factors: the nature of the soil, exposure to sun and wind, regularity of precipitation, chance colonizations, and many other arbitrary processes.

Keywords: unpredictable, precipitation, chance colonizations

Keyword Location: Para B, Lines 12-13

Explanation: The paragraph discusses how many arbitrary processes (random factors) make the specific details of succession unpredictable.

18. Disagreements over the meaning of an ecology term intended to identify the most stable ecosystem.

Answer: G

Supporting statement: Stability can be defined as simply lack of change.... Alternatively, stability can be defined as the speed with which an ecosystem returns to a particular form following a major disturbance, such as a fire. This kind of stability is also called resilience.

Keywords: Stability, ecosystem, resilience

Keyword Location: Para G, Lines 1-5

Explanation: This paragraph discusses two different, conflicting definitions of stability (lack of change vs. resilience) in the context of the climax community.

19. Mention of a new type of environment that is thought to increase stability by supporting a wide variety of organisms.

Answer: I

Supporting statement: Many ecologists now think that the relative long-term stability of climax communities comes not from diversity but from the “patchiness” of the environment, an environment that varies from place to place supports more kinds of organisms than an environment that is uniform.

Keywords: patchiness, environment

Keyword Location: Para I, Lines 2-3

Explanation: The paragraph introduces patchiness as the environmental factor (a type of environment) now believed to be the source of stability by supporting greater variety.

20. A reference to a new term that gradually replaced discredited terms for the combination of a physical environment and the plants and animals which live together there.

Answer: E

Supporting statement: With "climax," "biome," "superorganism," and various other technical terms... being criticized, the term "ecosystem" was more and more widely adopted for the whole system of associated organisms together with the physical factors of their environment.

Keywords: criticized, associated organisms

Keyword Location: Para E, Lines 2-3

Explanation: The paragraph shows that the term "ecosystem" replaced the earlier criticized terms.

QUESTIONS 21-25

DO THE FOLLOWING STATEMENTS AGREE WITH THE INFORMATION GIVEN IN THE READING PASSAGE? IN BOXES 21-25 ON YOUR ANSWER SHEET, WRITE

TRUE if the statement agrees with the information

FALSE if the statement contradicts the information

NOT GIVEN if there is no information on this.

21. Areas that are recovering from serious disturbances like volcanic eruptions provide opportunities to observe the development of plant communities.

Answer: TRUE

Supporting statement: The American ecologist Frederic Clements pointed out that a succession of plant communities would develop after a disturbance such as a volcanic eruption, heavy flood, or forest fire.

Keywords: Frederic Clements, volcanic eruption

Keyword Location: Para A, Lines 3-4

Explanation: The text explicitly uses disturbances like volcanic eruptions as examples where the succession of plant communities (their development) can be observed.

22. Climax communities last longer than any other type of community.

Answer: TRUE

Supporting statement: Pioneer and successional plant communities are said to change over periods of 1 to 500 years…… Climax communities themselves change but over periods of time greater than about 500 years.

Keywords: communities, 500 years

Keyword Location: Para B, Lines 3-5

Explanation: The text explicitly states that climax communities change over longer time periods (greater than 500 years) than the pioneer and successional stages (1 to 500 years), meaning they are the longest-lasting type mentioned.

23. According to Clements, the development of plant communities proceeds in a lawlike fashion and results in unstable climax communities.

Answer: FALSE

Supporting statement: Nevertheless, mature natural environments are usually in equilibrium ……..Clements and other early ecologists saw an almost lawlike regularity in the order of succession

Keywords: Clements, ecologists, natural environments

Keyword Location: Para B, Lines 8-10

Explanation: Clements believed in a lawlike regularity, but he saw the resulting mature community (climax) as being in equilibrium, which means stable, directly contradicting the claim that it results in unstable communities.

24. Climax communities are the most resilient communities, as they change the least over time.

Answer: FALSE

Supporting statement: Stability can be defined as ... resilience... In that case, climax communities would be the most fragile and the least stable, since they can require hundreds of years to return to the climax state.

Keywords: fragile, climax state

Keyword Location: Para G, Lines 6-7

Explanation: The text defines resilience and then immediately states that under this definition, climax communities are the least stable (or least resilient), contradicting the statement. The fact that they change the least over time is related to the other definition of stability (lack of change).

25. Redwood forests are found in temperate zones.

Answer: TRUE

Supporting statement: At least in temperate zones, maximum diversity is often found in mid-successional stages, not in the climax community. Once a redwood forest matures, for example...

Keywords: temperate zones, redwood forest matures

Keyword Location: Para H, Lines 2-3

Explanation: The redwood forest is used as an example to illustrate a point being made about temperate zones, establishing that redwood forests are indeed a feature of temperate ecology.

QUESTIONS 26-28

CHOOSE THE CORRECT LETTER, A, B, C, OR D.

26. Why do many ecologists refer to the term "association' to "community' when describing a climax plant formation?

A. Because the term "association" does not suggest the presence of a tight network involving interactive communication.

B. Because the term "association" indicates that the grouping is not necessarily beneficial to all members.

C. Because the term "community" indicates continuing dynamic development that a climax formation does not have.

D. Because the term "community" suggests an organization that has been designed for a specific purpose

Answer: A

Supporting statement: Many authors prefer the term "association" to the term "community" in order to stress the looseness of the interaction.

Keywords: association, community

Keyword Location: Para C, Line 7

Explanation: The use of the term "community" carries the baggage of Clements' idea of a "superorganism" (a tight, communicating entity like an ant colony). Ecologists prefer "association" to emphasize the looseness of the interaction

27. The idea of biome was challenged by the fact that

A. plants and animals respond in the same way to the same circumstances

B. particular combinations of flora and fauna do not generally come about purely by chance

C. there are usually no strong connections among the plants and animals living in a place

D. some animals are dependent on specific kinds of plants for food

Answer: C

Supporting statement: it is misleading to speak of a "spruce-moose biome," for example, because there is no internal cohesion to their association as it would be with an organism. The spruce community is not substantially affected by either the presence or absence of moose.

Keywords: spruce-moose biome, organism

Keyword Location: Para D, Lines 4-5

Explanation: The criticism of the "biome" concept stems from the lack of internal cohesion (strong connections/dependency) between the coexisting flora and fauna. The example shows spruce doesn't need the moose.

28. Gleason's opposition to the Clementsian views of plant ecology was based on the claim that plant species grow in places where

A. they can enter into mutually beneficial relationships with other species

B. conditions suit them, regardless of whether particular other species are present

C. habitats are available for a wide variety of plant and animal

D. their requirements are met, and those of most other species are not

Answer: B

Supporting statement: Their major point was that the distribution of a given species was controlled by the habitat requirements of that species and that, therefore, the vegetation types were a simple consequence of the ecologies of individual plant species.

Keywords: habitat requirements, vegetation types

Keyword Location: Para D, Lines 9-10

Explanation: Herbert Gleason's view was that individual species grow based purely on whether the habitat requirements (conditions) suit that species, arguing against the Clementsian view that they exist as a highly integrated community.

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