HS-LS2-6: Ecosystem Stability and Change
Also called NGSS HS-LS2-6 · Topic: Interdependent Relationships in Ecosystems · Life Science
The Official Wording
Evaluate claims, evidence, and reasoning that the complex interactions in ecosystems maintain relatively consistent numbers and types of organisms in stable conditions, but changing conditions may result in a new ecosystem.
Clarification statement: Examples of changes in ecosystem conditions could include modest biological or physical changes, such as moderate hunting or a seasonal flood; and extreme changes, such as volcanic eruption or sea level rise.
NGSS Lead States, 2013 · Read it on nextgenscience.org · checked October 15, 2026
What HS-LS2-6 Means in Plain English
Students weigh claims, evidence and reasoning about how ecosystems stay steady. In stable conditions, feeding links and competition keep the kinds and numbers of organisms roughly the same, but a big disturbance, such as an eruption or rising seas, can produce a different ecosystem.
Students judge the strength of each argument, separating modest changes like a dry summer from extreme ones like a lava flow. It builds on MS-LS2-4 and leads to HS-LS2-7 and HS-LS4-5, where changing conditions reshape habitats and species.
HS-LS2-6 I Can Statements
- I can evaluate whether evidence supports a claim about ecosystem stability.
- I can tell a modest disturbance from one that creates a new ecosystem.
- I can explain how interactions keep populations fairly steady.
HS-LS2-6 Worked Example
The 1980 eruption of Mount St. Helens in Washington gives students a real disturbance to argue about, backed by decades of field observations.
Is the land around Mount St. Helens returning to the old forest, or becoming a new ecosystem?
Set It Up: Before-and-after photos of the blast zone and the pumice plain, short field notes on which plants and animals returned, and a claim, evidence and reasoning chart.
- Read Claim A: the forest will come back just as it was.Claim A: full recovery
- Read Claim B: the pumice plain is becoming a different community.Claim B: new ecosystem
- Sort the evidence: pocket gophers survived underground and churned up old soil, and prairie lupine took root on bare pumice.Survivors and pioneers
- Compare areas that kept snow cover or soil with areas buried in deep pumice.Patches with survivors recovered faster
- Decide which claim fits each area and explain why.A mixed verdict, area by area
Places where soil and survivors remained are regrowing toward forest, while the deeply buried pumice plain is building a new community of meadow plants and shrubs.
Why it works: Interactions hold an ecosystem steady only while conditions stay within a range, and a disturbance that strips away soil and life resets which species can live there.
Common Mistakes with HS-LS2-6
Calling every change a new ecosystem
“The river flooded, so it is a whole new ecosystem now”
Try this: Ask how big the change was. Modest disturbances like a seasonal flood shift numbers briefly, and the community bounces back to a similar mix.
Thinking stable means unchanging
“A stable forest has exactly the same number of deer every year”
Try this: Stable ecosystems still go up and down. Numbers swing around a steady average because predators, prey and resources keep pulling them back.
Accepting a claim without weighing evidence
Agreeing with the claim that sounds most hopeful
Try this: Check each claim against the data. Ask whether the evidence is relevant, whether there is enough of it, and whether the reasoning connects them.
Where HS-LS2-6 Fits
Practice HS-LS2-6
Quick Check
- Give one example of a modest disturbance and one extreme one.
- Why did pocket gophers matter in the Mount St. Helens recovery?
- What makes evidence strong enough to support a claim?