Science · 7th Grade · Ecosystems: Interactions, Energy, and Dynamics · Quarter 4

Ecosystem Change and Stability

Learn how ecosystems respond to disturbances, both natural and human-caused, and explore the importance of biodiversity for maintaining stability.

TL;DR:Dive into the dynamic world of ecosystems to discover why some can weather a storm while others fall apart.

• Common Core State Standards
• NGSS: MS-LS2 - Ecosystems: Interactions, Energy, and Dynamics - Constructing an Argument about how Changes to Physical or Biological Components Affect Populations

About This Topic

This topic aligns with the Next Generation Science Standards (NGSS), particularly MS-LS2-4, which asks students to construct an argument supported by empirical evidence that changes to physical or biological components of an ecosystem affect populations. The core of this unit is understanding that ecosystems are not static, but dynamic systems constantly in flux. The lesson should explore the concepts of ecosystem resistance, the ability to withstand disturbance, and resilience, the ability to recover after a disturbance. A key theme is the role of biodiversity as a crucial factor in promoting both. Greater biodiversity often leads to more complex food webs and functional redundancy, which can buffer the ecosystem against shocks like disease, invasive species, or climate events.

Instruction should guide students from foundational concepts like ecological succession (both primary and secondary) to analyzing complex, real-world scenarios. It is essential to differentiate between natural disturbances, such as wildfires or floods which can be integral to an ecosystem's life cycle, and human-caused disturbances like pollution, habitat fragmentation, and the introduction of invasive species. By examining case studies, students can analyze data and evaluate the cascading effects of these changes, fostering a deeper understanding of environmental stewardship and the interconnectedness of living systems.

Key Questions

1. Analyze the factors that contribute to an ecosystem's resilience after a forest fire.
2. Explain the process of ecological succession on a newly formed volcanic island.
3. Evaluate how a loss of biodiversity might affect an ecosystem's ability to withstand environmental changes.

Learning Objectives

• Analyze how biodiversity contributes to the stability and resilience of an ecosystem.
• Differentiate between natural and human-caused disturbances and their respective impacts.
• Model the process of ecological succession after a major environmental change.
• Construct an evidence-based argument explaining how a change in one part of an ecosystem can affect the whole system.

Key Vocabulary

Biodiversity	The variety of life in a particular habitat or ecosystem.
Disturbance	An event, caused by physical, chemical, or biological agents, that results in changes in population size or community composition.
Resilience	The ability of an ecosystem to recover quickly after a disturbance.
Ecological Succession	The process by which the mix of species and habitat in an area changes over time.
Keystone Species	A species on which other species in an ecosystem largely depend, such that if it were removed the ecosystem would change drastically.
Stability	The tendency of an ecosystem to maintain its structure and function over time, despite disturbances.

Watch Out for These Misconceptions

Common Misconception

Ecosystems are static and unchanging.

What to Teach Instead

Ecosystems are dynamic and are constantly changing. Stability does not mean a lack of change, but rather the ability to resist or recover from disturbances through processes like ecological succession.

Common Misconception

All environmental changes are harmful to an ecosystem.

What to Teach Instead

Some disturbances, like seasonal flooding in floodplains or natural fires in certain forests, are a necessary part of the ecosystem's cycle. These events can clear out old growth, release nutrients into the soil, and create opportunities for new species to thrive.

Common Misconception

The loss of one species doesn't really matter in a large ecosystem.

What to Teach Instead

The loss of a single keystone species, like a top predator or a critical pollinator, can trigger a trophic cascade, causing drastic changes throughout the entire food web and potentially leading to the ecosystem's collapse.

Active Learning Ideas

Case Study Analysis

Biodiversity Jenga

Use a Jenga tower to represent an ecosystem, with each block symbolizing a species. Students take turns removing blocks, representing species loss, and observe how the tower's stability decreases, demonstrating that more diverse ecosystems (fuller towers) are more stable.

25 min·Small Groups

Case Study Analysis

Ecosystem Disturbance Case Studies

In small groups, students research a specific environmental event, such as the reintroduction of wolves to Yellowstone or the impact of zebra mussels in the Great Lakes. They present their findings on the causes, the effects on the ecosystem's stability, and the response.

90 min·Small Groups

Case Study Analysis

Succession in a Jar

Students create a simple aquatic ecosystem in a sealed jar with pond water, sand, and a few aquatic plants. They observe the changes over several weeks, noting how the community of microorganisms and plants develops and changes over time, modeling ecological succession.

120 min·Pairs

Real-World Connections

• Analyzing the impact of deforestation in the Amazon rainforest on global climate patterns and biodiversity.
• Understanding how overfishing can lead to the collapse of marine ecosystems and affect coastal economies.
• Evaluating urban planning strategies, like creating green spaces and wildlife corridors, to support local ecosystems.
• Studying the effects of agricultural runoff on the health of nearby rivers and lakes, leading to algal blooms.
• Participating in local conservation efforts to remove invasive species from a park or nature preserve.

Assessment Ideas

Exit Ticket

Use an exit ticket asking students to predict three effects of removing a specific producer from a given food web.

Peer Assessment

Students research a real-world ecosystem disturbance and create a presentation or report. They must identify the cause, analyze the impact on biodiversity and stability, and propose a scientifically-sound restoration plan.

Quick Check

Students complete a K-W-L (Know, Want to Know, Learned) chart at the beginning and end of the unit to reflect on their learning journey and identify remaining questions.

Frequently Asked Questions

What is the difference between ecosystem resistance and resilience?

Resistance is an ecosystem's ability to withstand a disturbance without changing much. Resilience is an ecosystem's ability to recover and return to its original state after a disturbance has occurred. An ecosystem can have high resistance but low resilience, or vice versa.

How does biodiversity make an ecosystem more stable?

High biodiversity means there are many different species performing various roles. If one species is wiped out by disease or a predator, another species can often step in to fill its role, preventing the whole system from collapsing. It's like having more pillars holding up a roof.

Are humans always a negative force in ecosystems?

While human activities like pollution and deforestation cause significant harm, humans can also play a positive role. Restoration projects, reintroducing native species, creating protected areas, and adopting sustainable practices are all ways humans can help heal and maintain ecosystem stability.