TPO 3-3 The Long-Term Stability of Ecosystems

Stability can be defined as simply lack of change.

The Long-Term Stability of Ecosystems

Plant communities assemble themselves flexibly, and their particular structure depends on the specific history of the area.

Plant communities assemble themselves flexibly, and their particular structure depends on the specific history of the area.

Plant communities assemble themselves flexibly, and their particular structure depends on the specific history of the area.

Plant communities assemble themselves flexibly, and their particular structure depends on the specific history of the area.

Plant communities assemble themselves flexibly, and their particular structure depends on the specific history of the area.

Plant communities assemble themselves flexibly, and their particular structure depends on the specific history of the area.

Plant communities assemble themselves flexibly, and their particular structure depends on the specific history of the area.

Ecologists use the term “succession” to refer to the changes that happen in plant communities and ecosystems over time.

Ecologists use the term “succession” to refer to the changes that happen in plant communities and ecosystems over time.

The first community in a succession is called a pioneer community, while the long-lived community at the end of succession is called a climax community.

The first community in a succession is called a pioneer community, while the long-lived community at the end of succession is called a climax community.

Pioneer and successional plant communities are said to change over periods from 1 to 500 years.

These changes—in plant numbers and the mix of species—are cumulative.

These changes—in plant numbers and the mix of species—are cumulative.

An ecologist who studies a pond today may well find it relatively unchanged in a year’s time.

Individual fish may be replaced, but the number of fish will tend to be the same from one year to the next.

Individual fish may be replaced, but the number of fish will tend to be the same from one year to the next.

We can say that the properties of an ecosystem are more stable than the individual organisms that compose the ecosystem.

We can say that the properties of an ecosystem are more stable than the individual organisms that compose the ecosystem.

We can say that the properties of an ecosystem are more stable than the individual organisms that compose the ecosystem.

We can say that the properties of an ecosystem are more stable than the individual organisms that compose the ecosystem.

At one time, ecologists believed that species diversity made ecosystems stable.

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.

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.

Ecologists concluded that the apparent stability of climax ecosystems depended on their complexity.

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.

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.

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.

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.

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.

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.

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.

In contrast, a complex climax community, such as a temperate forest, will tolerate considerable damage from weather to pests.

In contrast, a complex climax community, such as a temperate forest, will tolerate considerable damage from weather to pests.

In contrast, a complex climax community, such as a temperate forest, will tolerate considerable damage from weather to pests.

In contrast, a complex climax community, such as a temperate forest, will tolerate considerable damage from weather to pests.

The question of ecosystem stability is complicated, however.

The first problem is that ecologists do not all agree what “stability” means.

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.

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.

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.

Ecologists are especially interested to know what factors contribute to the resilience of communities because climax communities all over the world are being severely damaged or destroyed by human activities.

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.

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.

Even the kind of stability defined as simple lack of change is not always associated with maximum diversity.

Even the kind of stability defined as simple lack of change is not always associated with maximum diversity.

Even the kind of stability defined as simple lack of change is not always associated with maximum diversity.

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.

Mathematical models of ecosystems likewise suggest that diversity does not guarantee ecosystem stability—just the opposite, in fact.

Mathematical models of ecosystems likewise suggest that diversity does not guarantee ecosystem stability—just the opposite, in fact.

Mathematical models of ecosystems likewise suggest that diversity does not guarantee ecosystem stability—just the opposite, in fact.

A more complicated system is, in general, more likely than a simple system to break down.

Ecologists are especially interested to know what factors contribute to the resilience of communities because climax communities all over the world are being severely damaged or destroyed by human activities.

Ecologists are especially interested to know what factors contribute to the resilience of communities because climax communities all over the world are being severely damaged or destroyed by human activities.

Ecologists are especially interested to know what factors contribute to the resilience of communities because climax communities all over the world are being severely damaged or destroyed by human activities.

Ecologists are especially interested to know what factors contribute to the resilience of communities because climax communities all over the world are being severely damaged or destroyed by human activities.

The destruction caused by the volcanic explosion of Mount St. Helens, in the northwestern United States, for example, pales in comparison to the destruction caused by humans.

We need to know what aspects of a community are most important to the community’s resistance to destruction, as well as its recovery.

We need to know what aspects of a community are most important to the community’s resistance to destruction, as well as its recovery.

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.

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.

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.

A local population that goes extinct is quickly replaced by immigrants from an adjacent community.

A local population that goes extinct is quickly replaced by immigrants from an adjacent community.

A local population that goes extinct is quickly replaced by immigrants from an adjacent community.

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.

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.

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.

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.

Paragraph 1: Plant communities assemble themselves flexibly, and their particular structure depends on the specific history of the area.

The word “particular” in the passage is closest in meaning to ○natural ○final ○specific ○complex 2.

The word “particular” in the passage is closest in meaning to ○natural ○final ○specific ○complex 2.

According to paragraph 1, which of the following is NOT true of climax communities?

○They occur at the end of a succession.

According to paragraph 2, which of the following principles of ecosystems can be learned by studying a pond?

According to paragraph 2, which of the following principles of ecosystems can be learned by studying a pond?

○A change in the members of an organism does not affect an ecosystem’s properties.

According to paragraph 3, ecologists once believed that which of the following illustrated the most stable ecosystems?

○Ecologists often confuse the word “stability” with the word “resilience.”

○The exact meaning of the word “stability” is debated by ecologists.

○The exact meaning of the word “stability” is debated by ecologists.

○There are many different answers to ecological questions.

○They are more resilient than pioneer communities.

○They are stable because they recover quickly after major disturbances.

Which of the following can be inferred from paragraph 5 about redwood forests?

The word “guarantee” in the passage is closest in meaning to ○increase ○ensure ○favor ○complicate 9.

The word “guarantee” in the passage is closest in meaning to ○increase ○ensure ○favor ○complicate 9.

The word “guarantee” in the passage is closest in meaning to ○increase ○ensure ○favor ○complicate 9.

In paragraph 5, why does the author provide the information that “A fifteen-speed racing bicycle is more likely to break down than a child’s tricycle”?

In paragraph 5, why does the author provide the information that “A fifteen-speed racing bicycle is more likely to break down than a child’s tricycle”?

○To illustrate a general principle about the stability of systems by using an everyday example

○To demonstrate that an understanding of stability in ecosystems can be applied to help understand stability in other situations

○To demonstrate that an understanding of stability in ecosystems can be applied to help understand stability in other situations

○To demonstrate that an understanding of stability in ecosystems can be applied to help understand stability in other situations

○To demonstrate that an understanding of stability in ecosystems can be applied to help understand stability in other situations

○To make a comparison that supports the claim that, in general, stability increases with diversity

○To provide an example that contradicts mathematical models of ecosystems

The word “pales” in the passage is closest in meaning to ○increases proportionally ○differs ○loses significance ○is common

11．Which of the sentences below best expresses the essential information in the highlighted sentence in the passage?

11．Which of the sentences below best expresses the essential information in the highlighted sentence in the passage?

11．Which of the sentences below best expresses the essential information in the highlighted sentence in the passage?

Incurred choices change the meaning in important ways or leave out essential information.

○A patchy environment is thought to increase stability because it is able to support a wide variety of organisms.

12．The word “adjacent” in the passage is closest in meaning to ○foreign ○stable ○fluid ○neighboring

12．The word “adjacent” in the passage is closest in meaning to ○foreign ○stable ○fluid ○neighboring

█ 13．Look at the four squares [█] that indicate where the following sentence could be added to the passage.

In fact, damage to the environment by humans is often much more severe than damage by natural events and processes.

In fact, damage to the environment by humans is often much more severe than damage by natural events and processes.

In fact, damage to the environment by humans is often much more severe than damage by natural events and processes.

14．Directions: An introductory sentence for a brief summary of the passage is provided below.

14．Directions: An introductory sentence for a brief summary of the passage is provided below.

14．Directions: An introductory sentence for a brief summary of the passage is provided below.

Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage.

Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage.

Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage.

○The changes that occur in an ecosystem from the pioneer to the climax community can be seen in one human generation.

○A high degree of species diversity does not always result in a stable ecosystem.

○The level of resilience in a plant community contributes to its long-term stability.

○Disagreements over the meaning of the term “stability” make it difficult to identify the most stable ecosystems.

○Disagreements over the meaning of the term “stability” make it difficult to identify the most stable ecosystems.