Dynamic and Resilient Ecosystems

Dynamic and Resilient Ecosystems

Middle School

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Learning Objectives

• Define primary succession and the role of pioneer species in building soil.

• Compare and contrast primary and secondary succession.

• Explain ecosystem resilience and how scientists study successional changes.

• Identify human impacts on succession and actions to protect it.

Key Vocabulary

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Primary Succession

The slow, predictable change from bare rock to a complex community of organisms over a long period.

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Pioneer Species

Pioneer species are the first tough organisms to live in an area with little water or nutrients.

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Weathering

This is the natural process that breaks down large rocks into much smaller particles through different means.

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Soil

Soil is a mixture of mineral particles, decayed organic matter called humus, along with air and water.

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Facilitation

This occurs when early species change the environment in ways that help later species to grow successfully.

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Biodiversity

Biodiversity refers to the variety of different species that are living within a particular habitat or ecosystem.

Key Vocabulary

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Resilience

The ability of an ecosystem to recover and bounce back after a disturbance or shock.

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Chronosequence

A method using sites of different ages to study ecological changes over time.

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Dynamic Mosaic

A mature ecosystem viewed as a patchwork of communities at different stages of succession.

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Primary Succession: Life from Scratch

• Primary succession starts on new land, like a lava flow, with no soil.

• The rocky, barren land is weathered by wind and rain, creating mineral dust.

• Tough pioneer species like lichens and mosses arrive and create the first soil.

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Multiple Choice

What is the defining characteristic of an environment where primary succession begins?

• It begins in an area that has no soil.

• It requires a large number of trees to get started.

• It happens only in areas with heavy rainfall.

• It is a process that happens very quickly.

Multiple Choice

What is the primary role of pioneer species like lichens and mosses in the process of primary succession?

• They create the first soil on the barren rock.

• They provide shade for other plants to grow.

• They are a food source for the first animals.

• They break down large rocks into sand.

Multiple Choice

Following a volcanic eruption that leaves behind a field of barren lava rock, what must occur first before a forest can eventually develop?

• Weathering and pioneer species must create soil.

• Seeds from large trees must arrive by wind.

• The rock must be completely covered by water.

• Animals must return to fertilize the ground.

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Building the Foundation of an Ecosystem

• Soil forms from weathered mineral particles mixed with organic matter called humus.

• Plants colonize in stages, starting with grasses, then shrubs, and finally trees.

• As the ecosystem grows, biodiversity, biomass, and food webs become more complex.

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Multiple Choice

What is soil primarily made of?

• Weathered mineral particles and organic matter

• Only grasses and shrubs

• Just water and air

• Only complex food webs

Multiple Choice

Which of the following describes the typical sequence of plant growth in a developing ecosystem?

• Trees, followed by shrubs, and then grasses

• Grasses, followed by shrubs, and then trees

• Shrubs, followed by grasses, and then trees

• All plant types appear at the same time

Multiple Choice

If a barren field of weathered rock and humus is left undisturbed for a century, what is the most likely outcome?

• The biodiversity and biomass in the area will increase.

• The amount of organic matter in the soil will decrease.

• The food webs will become simpler.

• Only trees will be found in the area.

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Mechanisms of Change

Primary Succession

• Begins on bare rock surfaces where no soil is present.

• This type of succession is a very slow process.

• Pioneer species like lichens and mosses must create new soil.

Secondary Succession

• Starts in an area where a previous ecosystem existed and soil is intact.

• This type of succession is a much faster process.

• It typically begins with the growth of small herbs and grasses.

Multiple Choice

What is the fundamental difference that determines whether primary or secondary succession will occur in an area?

• The types of animals that eventually return to the area.

• The presence or absence of soil at the beginning of the process.

• The speed at which the final ecosystem is established.

• The climate in which the ecosystem is located.

Multiple Choice

Which statement best explains the difference in speed between primary and secondary succession?

• Primary succession is slowed down by the presence of too many large trees.

• Secondary succession only occurs in warm climates with high rainfall.

• Secondary succession begins with intact soil, allowing plants like grasses to grow quickly.

• Primary succession is faster because lichens can grow on any surface.

Multiple Choice

A massive landslide scrapes away all soil and plant life from a mountainside, leaving only bare rock. What is the most likely ecological process to occur next?

• Secondary succession will quickly begin, with grasses and herbs sprouting from the existing soil.

• Primary succession will slowly begin, starting with lichens colonizing the bare rock to create soil.

• The area will remain as bare rock permanently because the ecosystem was destroyed.

• A mature forest will immediately grow back because the area was previously a forest.

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A Dynamic and Resilient System

• Resilience is an ecosystem's ability to recover, aided by seed banks and dispersal.

• The process of succession is slow, taking centuries for forests to develop.

• Ecosystems are a dynamic mosaic, a patchwork constantly reshaped by natural disturbances.

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Multiple Choice

What does it mean for an ecosystem to be resilient?

• Its ability to recover after a disturbance.

• The variety of animals within the system.

• The slow development of forests over time.

• Its patchwork-like appearance from above.

Multiple Choice

Why is an ecosystem described as a 'dynamic mosaic'?

• It is constantly being reshaped by natural disturbances.

• It takes centuries for new forests to fully develop.

• It relies on seed banks for its survival.

• It is able to recover quickly from any change.

Multiple Choice

After a large wildfire burns a section of a forest, what is the most likely outcome over time?

• The forest will slowly recover over a long period through the process of succession.

• The forest will be unable to recover because the disturbance was too large.

• The forest will be replaced by a new ecosystem within a few years.

• The forest will immediately return to its original state due to seed dispersal.

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How We Study Succession

• Scientists use a chronosequence to compare similar sites of different known ages.

• They use tools like transects and quadrats to measure plants and soil depth.

• Soil depth and plant height are expected to increase with the site's age.

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Multiple Choice

What is the main purpose of using a chronosequence for studying an ecosystem?

• To compare similar sites of different known ages.

• To measure the exact height of every plant in an area.

• To count the number of different animal species.

• To increase the speed of plant growth at a site.

Multiple Choice

What is the relationship between tools like transects and quadrats and the study of succession?

• To determine the age of the rocks in the area.

• To measure physical characteristics like plant size and soil depth.

• To identify the types of clouds above the site.

• To speed up the rate of ecological succession.

Multiple Choice

A scientist compares a 20-year-old forest site with a 100-year-old forest site. What is the most likely prediction based on the principles of succession?

• The 20-year-old site will have taller plants and deeper soil.

• The 100-year-old site will likely have taller plants and deeper soil.

• Both sites will have identical plant height and soil depth.

• Neither site will have any soil or plants.

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Common Misconceptions

Misconception	Correction
Succession is a linear race to one final 'climax' stage.	Succession creates a dynamic patchwork of habitats at different stages.
Soil is just inanimate dirt or crushed rock.	Soil is a living mix of minerals, air, water, and organic matter.
Pioneer species are weak because they are small and simple.	Pioneer species are tough and specialized to survive in harsh conditions.

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Summary

• Primary succession starts on new, soilless land with pioneer species like lichens.

• Pioneer species create soil, allowing grasses, shrubs, and then forests to grow.

• This slow process increases biodiversity and is much slower than secondary succession.

• Ecosystems form a dynamic mosaic of habitats at different stages of growth.

Poll

On a scale of 1-4, how confident are you about explaining the process of primary succession on a volcanic island?

• 1

• 2

• 3

• 4