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B3.5 · Explain how biodiversity supports viable, resilient ecosystems

Learn to explain how biodiversity supports viable, resilient ecosystems through clear examples and targeted practice.

Ontario Grade 11 Biology

Diversity of Living Things

How living variety helps ecosystems continue and recover

In SNC2D, you learned that an ecosystem includes living things and their surroundings, and that parts of a system can affect one another. Consider a meadow with several kinds of flowering plants. If one kind flowers poorly in a particular year, other plants may still provide food for insects. This example raises a key question: how can variety among living things help an ecosystem keep functioning? Biodiversity is the variety of living things. In this lesson, you will connect that variety to ecosystem viability and resilience.

What you will learn

Define biodiversity, ecosystem viability, and resilience.
Explain how variety among living things can support important ecosystem functions.
Use a simple food-web model to reason about possible effects of change.
Distinguish an observed pattern from a possible explanation.

From ecosystem systems to the biodiversity question

An ecosystem includes organisms, such as plants and animals, and non-living parts of their surroundings, such as water, soil, and light. Organisms can affect one another. For example, an insect may feed on a plant, and a bird may eat the insect. These connections help make an ecosystem a system rather than just a list of species.

Biodiversity means the variety of life in a place. It can include variety among species, variety within a species, and variety among ecosystems. A species is a group of similar organisms that can reproduce with one another. In this lesson, the main focus is how variety in living things supports ecosystems.

A viable ecosystem is one that can continue to support its living communities and important functions over time. Resilience is the ability of an ecosystem to withstand a disturbance or recover after one. A disturbance is a change that affects organisms or their surroundings, such as a dry period, a storm, or the loss of a species. Viability and resilience are related, but they are not identical: viability concerns continued functioning, while resilience concerns response to change.

Biodiversity is variety in life, not simply the number of individual organisms.
Ecosystem functions include processes such as providing food and supporting pollination.
Resilience describes response to disturbance; viability describes continued ability to function.

How variety can support ecosystem functions

A food web is a model of feeding relationships in an ecosystem. An arrow in a food web points from the organism being eaten to the organism that eats it. Food webs help show that one organism may be connected to several others.

Different species can contribute to different functions. Flowering plants can provide food for pollinators. In turn, some pollinators help plants reproduce by moving pollen between flowers. Decomposers, such as many fungi and bacteria, break down dead material and return materials to the environment. These examples show that ecosystems depend on interacting living things.

Sometimes more than one species can contribute to a similar function. If one food source becomes less available, another may still be used by some consumers. This does not guarantee that the ecosystem will be unaffected. It suggests one way that variety can reduce the chance that a change in one species stops a function completely.

Variety within a species can also matter. Individuals of the same species may differ in their features. If conditions change, some individuals may be better able to survive and reproduce under the new conditions than others. This can help the species persist. It does not mean every individual will survive, or that the species is certain to adapt.

Biodiversity can therefore support resilience in more than one way: different species may contribute to related functions, and differences among individuals may mean that not all respond to a disturbance in the same way. The result depends on the ecosystem and the disturbance. More biodiversity does not make an ecosystem invulnerable. biodiversity → possible support for ecosystem functions and resilience

Food webs represent feeding connections, but they are models rather than complete pictures of every interaction.
Species variety can provide more than one route for some ecosystem functions.
Differences among individuals may affect how a species responds to changing conditions.

Evidence, models, and careful conclusions

Biologists can observe patterns, such as an ecosystem with greater variety continuing to show certain functions after a disturbance. An observation describes what was found. An explanation proposes why the pattern occurred. The pattern alone does not prove that biodiversity caused the outcome. Other conditions, such as the type or strength of disturbance, may also matter.

A food web is useful for making a prediction. If a species disappears, the web can help identify organisms that might lose a food source or experience less competition. But a food web may leave out interactions, changes over time, or differences in how strongly organisms depend on one another. Predictions from the model should therefore be treated as possibilities, not certainties.

When explaining a biodiversity pattern, connect evidence to a plausible function. For example, if several plant species provide food for pollinators at different times, that variety could help keep food available across a longer period. The model explains a possible link; observations would be needed to determine whether it happens in a particular place.

Separate what was observed from the explanation proposed for it.
Use food webs to reason about possible effects, not to claim certainty.
Explain resilience through specific connections or functions.

A useful explanation structure

A strong answer to B3.5 names the kind of biodiversity involved, identifies an ecosystem function, and explains how variety could help that function continue during or after change. It should also avoid claiming that biodiversity prevents every harm.

For example, a student might describe several flowering plant species as a source of variety. The student could then explain that if one plant produces fewer flowers during a dry period, other plants may still provide some food for pollinators. This could help maintain a feeding connection, although the result depends on which plants and pollinators are present and how severe the dry period is.

This reasoning moves from a concrete feature, to an ecosystem function, to a possible effect on resilience. It is more precise than saying only that biodiversity is good for nature.

Name the biodiversity, function, and possible effect.
Use cautious wording such as “could” when the outcome depends on conditions.
Do not confuse support for resilience with a guarantee of recovery.

Worked example

A meadow after a dry period

A meadow contains several flowering plant species. During a dry period, one species produces few flowers, while other species still flower. Explain how this variety could support resilience. Treat the situation as a model, not as measured field data.

Identify the variety
The meadow has several plant species, so it has species variety. The dry period is the disturbance in this example.
Connect variety to a function
Flowering plants can provide food for pollinators. Since some plant species still flower, some food may remain available even when one species produces few flowers.
State a careful conclusion
The variety could help maintain this food source and support resilience. It does not prove that pollinators will be unaffected, because the remaining flowers may not meet their needs and other conditions may matter.

Answer: Several flowering plant species could help keep some food available to pollinators when one species flowers poorly. This may support resilience, but it does not guarantee that pollinators or the meadow will be unaffected.

Check: The explanation names the variety, links it to a function, and avoids treating a possible benefit as certain.

Worked example

Reasoning with a simple food web

In a simplified food web, two plant species provide food for an insect, and the insect is food for a bird. Suppose one plant species becomes less common. Explain one possible consequence and one reason the result is uncertain.

Trace the feeding connection
The insect has two plant food sources in the model. If one becomes less common, that source may provide less food to the insect.
Consider the other connection
The second plant may still provide food. This is one way species variety could help preserve a feeding connection in the food web.
Limit the prediction
The insect may still decline if the remaining plant is not enough or cannot be used as food. The bird could then have less insect food. The food web suggests these possibilities, but does not tell us exactly what will happen.

Answer: The insect may have less food from the plant that became less common, but the second plant could provide another food source. The effect on the insect and bird is uncertain because the simplified food web does not show how much each species depends on each connection.

Check: The reasoning follows the feeding links and distinguishes a possible outcome from a guaranteed one.

Worked example

A pattern and its possible explanation

Imagine that observations from two ecosystems show that one ecosystem with more species continues to support a feeding function after a disturbance, while the other does not. Give a possible explanation and state why the observation alone does not prove it.

Describe the observation
The observed pattern is that the ecosystem with more species continued to show the feeding function after the disturbance. This describes the comparison without yet explaining it.
Offer a possible model
One possible explanation is that more than one species could contribute to the feeding function, so the loss or decline of one species did not remove every route that supported it.
Name a limitation
The observation alone does not show that biodiversity caused the difference. The ecosystems may have faced disturbances of different strength or differed in other relevant ways. More evidence would be needed to assess the explanation.

Answer: Species variety could have provided more than one way to support the feeding function. However, the comparison alone does not establish cause, because other differences between the ecosystems could also explain the pattern.

Check: A complete answer separates the observed result, a plausible explanation, and a limitation.

Common mistakes and how to avoid them

“An ecosystem with high biodiversity cannot be damaged.”

Correction: Biodiversity can support resilience, but disturbances can still harm species and ecosystem functions.

“More species always means every function will continue.”

Correction: The effect depends on which species are present, how they interact, and the disturbance involved.

“A food-web model proves exactly what will happen.”

Correction: A food web shows selected connections. It helps identify possibilities but may leave out important details.

“An observed pattern proves its proposed explanation.”

Correction: An observation describes a result. Other evidence is needed to decide whether a proposed explanation is supported.

Lesson summary

Biodiversity is variety in life, including variety among species and within a species.
Ecosystem viability concerns continued functioning; resilience concerns withstanding or recovering from disturbance.
Biodiversity can support functions by providing different species or individuals that may respond differently to change.
Food webs help explain possible effects, but they are simplified models and do not guarantee a particular outcome.
Good explanations connect biodiversity to a specific function and use cautious conclusions.

Check your understanding

Question 1

A wetland has several plant species, and some still provide food when one species becomes scarce. Which statement best explains a possible benefit?

The remaining plants could help keep a food source available, supporting resilience.
The wetland is guaranteed to recover from every disturbance.
The plants prove that no animal in the wetland will lose food.
Biodiversity means that all plant species perform exactly the same role.

Show answer and explanation

The remaining plants could help keep a food source available, supporting resilience.

Other plants could help maintain a food source, but this is not a guarantee. Their actual contribution depends on the organisms and conditions involved.

Question 2

A food web suggests that a bird may have fewer food sources if one insect species declines. What is the most careful conclusion?

The bird will certainly disappear.
The model points to a possible risk, but it may not show every food source or interaction.
The food web proves that the insect decline has no effect.
The bird will always switch to a different food source.

Show answer and explanation

The model points to a possible risk, but it may not show every food source or interaction.

A food web helps identify possible effects, but a simplified model cannot establish exactly what will happen.

Question 3

What is the difference between viability and resilience?

Viability is continued ability to function; resilience is the ability to withstand or recover from disturbance.
Viability means having many species; resilience means having no disturbances.
Viability is a type of food web; resilience is a type of species.
The terms mean exactly the same thing.

Show answer and explanation

Viability is continued ability to function; resilience is the ability to withstand or recover from disturbance.

Viability focuses on continued ecosystem functioning. Resilience focuses on response to disturbance.

Key terms

Biodiversity: The variety of living things, including variety among species and within species.
Ecosystem: Living organisms in an area and the non-living parts of their surroundings, connected through interactions.
Food web: A model showing feeding relationships among organisms.
Disturbance: A change that affects organisms or their surroundings.
Viable ecosystem: An ecosystem able to continue supporting its living communities and important functions over time.
Resilience: The ability of an ecosystem to withstand a disturbance or recover after one.
Observation: A description of something noticed or recorded.
Model: A simplified representation used to show or reason about a system.

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About this lesson and its review

Published by DoAssignment. This reviewed lesson follows Ontario Grade 11 Biology (SBI3U), expectation B3.5. It is a study resource, not an official curriculum publication.

Before publication, content is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability. Errors can still occur, so corrections are welcomed.

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