HS-LS2-6: Evaluating Evidence for Ecosystem Stability and Change
In plain English: HS-LS2-6 is the NGSS high school performance expectation that asks students to evaluate the claims, evidence and reasoning that interactions in an ecosystem keep the numbers and types of organisms fairly steady when conditions are stable, while changing conditions can produce a new ecosystem. It is usually taught in Biology or Environmental Science.
Evaluate the 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.
Next Generation Science Standards · Disciplinary Core Idea: Ecosystems: Interactions, Energy, and Dynamics · Official standard
Students evaluate a two-part claim: in stable conditions, the many interactions in an ecosystem (predation, competition, disease, limited food and space) keep the numbers and types of organisms relatively consistent, and when conditions change enough, the ecosystem can become a new one. Students do not just state the claim. They judge the evidence (How long is the record? Is there a baseline? Is there a comparison site?) and the reasoning (Does it name the interactions that explain the pattern?). They compute means and percent changes to decide whether a change is small and temporary or large and lasting.
The NGSS Clarification Statement says: "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." HS-LS2-6 has no official Assessment Boundary. This lesson uses both kinds of change named in the Clarification Statement: modest ones (moderate hunting, a seasonal flood) and extreme ones (a volcanic eruption, sea level rise). All data sets are invented for teaching, and "within 15% of the mean" and similar cutoffs are class criteria for this lesson, not official definitions.
Learning Objectives
By the end of this lesson, students will be able to:
Use means and percent changes from population and species data to describe how consistent an ecosystem is over time
Evaluate the evidence for a claim about ecosystem stability: length of record, baseline, sample size and comparison sites
Evaluate the reasoning for such a claim by checking whether it names the interactions that keep numbers and types of organisms consistent
Distinguish modest changes, after which an ecosystem returns to about the same numbers and types of organisms, from extreme changes that can produce a new ecosystem
Write a critique of a claim, evidence and reasoning argument and suggest the evidence that would strengthen it
Prior Knowledge Required
Students should already be comfortable with:
Food webs and the interactions among organisms: predation, competition, mutualism MS-LS2-2
How changes to physical or biological parts of an ecosystem affect populations MS-LS2-4
Finding a mean and describing variability in a data set 6.SP.B.5
Show two photos side by side: a meadow in two different summers that look almost the same, and a hillside before and after a lava flow. Ask students to write privately first:
Warm-Up Prompt
"A park ranger says, 'This meadow never changes.' What would you need to measure, and for how many years, to decide whether she is right? What would make you say the lava hillside is a different ecosystem now, and not the same one recovering?"
Collect ideas on the board under "what to measure" (numbers of each species, which species are present) and "how long". Students often say "never changes" means exactly the same numbers; flag this idea for Direct Instruction.
Direct Instruction15-20 minutes
Stable does not mean unchanging. In stable conditions, populations rise and fall from year to year, but interactions pull them back: when prey are plentiful, predators do well and eat more of them; when a population is crowded, food runs short and disease spreads. The result is numbers that stay within a range around an average, and the same types of organisms year after year. After a modest change the ecosystem usually returns to about the same state. After an extreme change the old community may not return, and a different set of organisms can take over: a new ecosystem. To evaluate a claim, check three things: the claim (what exactly is said to be stable or new), the evidence (how many years, what baseline, any comparison site) and the reasoning (which interactions explain the pattern). Use Diagram 1 with the first example and Diagram 2 with the fourth.
Stable conditions: numbers within a range
Invented counts of meadow voles in a grassland over 8 years: 142, 158, 131, 150, 163, 139, 147 and 154 voles per hectare.
Result: Mean = 1,184 ÷ 8 = 148. The lowest year is (131 - 148) ÷ 148 = -11.5% and the highest is (163 - 148) ÷ 148 = +10.1%, so every year is within 15% of the mean: relatively consistent numbers.
Modest change: moderate hunting
An invented county forest held 420 deer before a regulated hunting season began. In the five hunting years the counts were 380, 368, 375, 371 and 378, and plant surveys found the same species as before.
Result: Mean in the hunting years = 1,872 ÷ 5 = 374.4, which is (374.4 - 420) ÷ 420 = -10.9%. The numbers settled at a new, slightly lower level, and the types of organisms did not change: the same ecosystem.
Modest change: seasonal flood
An invented floodplain plot had 24 plant species before a spring flood. Two weeks after the water went down, 21 were found. One year later, all 24 were back.
Result: 21 ÷ 24 = 87.5% of the species right after the flood, and 24 ÷ 24 = 100% a year later. A temporary dip followed by a return supports "same ecosystem".
Extreme change: volcanic eruption
An invented plot on a volcano had 38 plant species before an eruption buried it in ash and rock. After 20 years it had 29 species, but only 16 were on the original list (Diagram 2).
Result: Original species present = 16 ÷ 38 = 42.1%. New species = 29 - 16 = 13, which is 13 ÷ 29 = 44.8% of the plants now there. The types of organisms changed a lot: evidence for a new ecosystem.
Extreme change: sea level rise
In an invented coastal marsh, rising seas pushed salt water inland. Over 15 years the water salinity rose from 0.5 to 12 parts per thousand, cattail cover fell from 70% to 5% and salt-tolerant cordgrass cover rose from 0% to 55%.
Result: Cattail cover fell by (70 - 5) ÷ 70 = 92.9%, and a plant that was absent now covers more than half the marsh. The dominant organisms changed: a freshwater marsh became a salt marsh.
After each example ask: "Is this evidence about numbers, about types of organisms, or both? Is the record long enough? What interaction explains the pattern?"
Guided Practice15 minutes
Pairs evaluate this claim with the invented data below: "The kelp forest was stable for years, and the loss of sea otters produced a new ecosystem, an urchin barren." (Sea otters eat sea urchins, and urchins eat kelp.)
Guided practice data (invented): one stretch of rocky coast
Year
Sea otters per km of coast
Sea urchins per m²
Kelp cover (%)
1
11
2.1
62
2
10
1.8
58
3
12
2.4
65
4
11
2.0
60
5
10
1.7
59
6
7
6.5
45
7
5
12.0
30
8
4
19.5
16
9
3
24.0
9
10
3
26.0
7
Find the mean of each column for years 1-5. (Otters 10.8, urchins 2.0, kelp 60.8%.) Were years 1-5 relatively consistent?
Find the means for years 6-10. (Otters 4.4, urchins 17.6, kelp 21.4%.)
By what percentage is the year 10 kelp cover below the years 1-5 mean? (About 88.5%.)
Evaluate the reasoning: which interactions link the three columns? Does the claim explain the order of the changes?
Evaluate the evidence: what is missing before you could say the otter loss caused the change? Name one other possible cause and one kind of data that would test it.
Independent Practice10-15 minutes
Each student evaluates a new claim: "Opening the lake to moderate sport fishing destroyed the lake ecosystem." Invented data: the mean catch of yellow perch per survey net was 48, 52 and 50 in the three years before fishing opened, and 43, 41, 44 and 42 in the four years after. Surveys found the same 14 fish species before and after.
Students compute both means (50 and 42.5) and the percent change (-15%), then write a critique: which part of the claim the data support (a lower perch number), which part they do not (the types of fish did not change, and the new counts are steady), and what evidence would make the argument stronger.
Closure5 minutes
Exit ticket: "Sort these into modest and extreme changes, and predict for each whether the ecosystem is likely to return to about the same numbers and types of organisms: a moderate deer-hunting season; a lava flow covering a forest; a spring flood that drains in two weeks; seas that permanently flood a freshwater marsh with salt water." Then return to the warm-up and revise the ranger's claim so that it is testable.
Differentiation Strategies
For Struggling Students
Give a three-column organizer (claim, evidence, reasoning) with prompts such as "How many years of data?" and "Which interaction?"
Provide a percent-change frame: (new - old) ÷ old × 100, with the first data set worked on the page
Start with the two clearest cases (the vole data and the eruption plot) before the kelp data, which need more steps
For Advanced Students
Ask students to decide what cutoff (within 10%, 15% or 20% of the mean) they would use for "relatively consistent" and defend it with the vole and songbird data
Have students design a monitoring plan with a comparison site for a claim of their choice, including how many years and what they would count
Ask students to find a case in which a modest change repeated many times could add up to a new ecosystem, and explain the reasoning
Assessment Guidance
What to Look For
Check that students use both numbers and types of organisms as evidence, not only one population. Look for critiques that name a specific weakness (one year of data, no baseline, no comparison site, correlation offered as cause) and propose specific new evidence. Listen for students who think "stable" means "no change at all", or who call any drop in a population a new ecosystem. Check percent changes for the right base (the earlier value).
02
Classroom Activities
3 Activities
1
Claim Court: Four Ecosystem Arguments
25 minGroups of 3-4
Each group is a panel of judges. They receive four claim cards, each with an invented data set, and rate the claim, the evidence and the reasoning as strong, partial or weak. Then they write one sentence that would make each argument stronger.
Claim Cards
Card 1, prairie: "Moderate cattle grazing did not change the prairie." Grass species per plot: 22, 21, 23 in the three years before grazing and 22, 22, 21 in the three grazing years. Grass biomass: 510, 495, 520 g per m² before and 470, 480, 465 g per m² during.
Card 2, island: "Rats that arrived on the island produced a new ecosystem." Seabird nests: 1,200 in the year rats were first seen and 150 eight years later. Five of the 9 seabird species that nested there no longer do.
Card 3, coral reef: "The reef is stable because live coral covered 32% of the survey area this year." No other years are given.
Card 4, river: "The big flood destroyed the river ecosystem." Insect families per kick-net sample: 18 before, 7 one month after, 16 one year after and 18 two years after.
Discussion Questions
On Card 1, grass biomass during grazing is about 7% below the earlier mean. Is the claim supported, partly supported or not supported? Use both the species and the biomass data.
Card 3 has only one measurement. What would you need to evaluate the word "stable"?
Card 4 shows a large drop and then a return to 18 families. How does that change your verdict on the claim?
Modification for Distance Learning
Post the cards on a shared slide deck. Each group records its verdicts in a table and comments on one other group's ruling.
2
Yarn Food Web: Modeling Interactions
20 minWhole class (12 students hold cards; the rest record)
Twelve students wear species cards: oak trees, grasses, berry shrubs, mice, grasshoppers, deer, rabbits, songbirds, snakes, foxes, hawks and soil fungi. The class passes yarn between the cards for each of 18 feeding links, then models a modest change and an extreme change by tugging and by removing cards.
The 18 Links
Mice eat acorns from oaks and grass seeds; grasshoppers eat grasses; deer eat oaks, berry shrubs and grasses; rabbits eat grasses and berry shrubs; songbirds eat grasshoppers and berries; snakes eat mice and songbirds' eggs; foxes eat rabbits and mice; hawks eat snakes, rabbits and mice; fungi break down dead oak leaves and wood.
Procedure
Pass the yarn for every link and keep it taut. Recorders count the links at each card. (Mice have the most, 5.)
Modest change: the fox holder takes one step in (fewer foxes). Everyone who feels the yarn go slack raises a hand. Recorders note who responded.
Extreme change: the oak card leaves the circle. Everyone directly linked to the oak sits down, then anyone left with no food link also sits.
Safety: keep the yarn below shoulder height, walk only, and cut the web apart with blunt scissors at the end rather than pulling it over heads.
Discussion Questions
Removing the oak affected the mice, the deer and the fungi directly. Why did the deer and mice keep a food link while the fungi did not?
How does the web model the claim that complex interactions keep numbers consistent? What does it leave out (numbers of each species, time)?
Would removing the mice card be a larger or smaller change than removing the oak? Count the links to support your answer.
Variation: Adding a New Species
Add an invasive plant card that competes with the grasses and berry shrubs. Students predict which cards would change first, then argue whether the result is the same ecosystem.
3
Schoolyard Quadrat Survey: Collecting a Baseline
25 minGroups of 3
Groups collect real evidence about consistency by counting the plant types in 1 m² quadrats in two parts of the school grounds: a mowed lawn and an unmowed edge. They compare their means with last year's means from the same plots if an earlier class recorded them; otherwise they practice the comparison with the invented sample data below.
Safety
Stay inside the survey area and within sight of the teacher. Check the area first for broken glass, ant mounds, bee nests and plants such as poison ivy or poison oak.
Wear garden gloves when parting plants, do not taste or pick unknown plants or berries, and wash hands or use sanitizer afterward.
Students with bee-sting or plant allergies tell the teacher before going out and bring any prescribed medication. Wear sun protection on sunny days.
Procedure
Place five quadrats in each area at spots chosen by rolling dice for paces, not by picking the most interesting spots.
Count the number of different plant types in each quadrat (use the identification sheet, or describe unknown types as "Plant A", "Plant B").
Find the mean for each area and compare it with last year's mean.
Sample Data (invented)
This year, mowed lawn: 4, 5, 4, 3, 4 plant types per quadrat (mean 4.0). Unmowed edge: 9, 11, 10, 12, 8 (mean 10.0). Last year's means from the same plots: 4.2 and 10.4.
Discussion Questions
Both areas changed by less than 5% from last year. What do these results suggest about the conditions in each area, and why do the two areas hold such different numbers of plant types?
Why do we choose quadrat spots by rolling dice?
Two years of data is a short record. What would you need to collect to make a strong claim that the lawn is stable?
Modification for Distance Learning
Students survey a patch of yard, park or sidewalk cracks near home with a string quadrat, or use the sample data, and post their means with a short claim.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: Vole Counts in a Stable Grassland
The invented vole counts from the first worked example, drawn to scale. The counts rise and fall every year but stay inside the shaded band (within 15% of the mean of 148 voles per hectare, a class criterion). Predation, competition for food and disease pull the population back toward the mean.
Diagram 2: Plant Species Before and After an Eruption
The invented volcano plot from the fourth worked example, drawn to scale. The number of species recovers to 29 after 20 years, but only 16 of them were on the original list of 38. Numbers alone would suggest recovery; the types of organisms show that a new community has formed.
04
Homework Assignment
~30 min
HS-LS2-6 Homework: Evaluating Claims About Ecosystem Stability
Directions: All data sets are invented for practice. Show each calculation. For every claim, say whether the data support it, partly support it or do not support it, and explain using the claim, the evidence and the reasoning.
Part 1: Evidence of Stability (Problems 1-3)
A survey counted wood thrushes in the same forest for 10 years: 34, 38, 31, 36, 40, 33, 35, 37, 32 and 34 birds. (a) Find the mean. (b) Find the percent difference of the lowest and the highest year from the mean. (c) Evaluate the claim "The thrush population is relatively consistent" using a cutoff of 15%.
A student claims: "Wolves keep the elk herd at exactly the same size." Evidence: 1,200 elk last year and 1,180 this year. (a) Find the percent change. (b) Evaluate the evidence and the wording of the claim. (c) Describe the data you would need to support a revised claim.
A tide pool was surveyed each summer for four years. It had 18, 17, 18 and 19 species, and 16 species were found every year. (a) What percentage of the year 4 species were found every year? (b) Does this support the claim that the types of organisms stayed relatively consistent? (c) Name two interactions that could keep the community this steady.
Part 2: Evidence of Change (Problems 4-6)
In an invented grassland, plant biomass averaged 420 g per m² over five normal years. In a dry year it fell to 310 g per m², and the next year it was 405 g per m², with the same plant species throughout. (a) Find the percent drop in the dry year. (b) What percentage of the average was the next year's biomass? (c) Evaluate the claim "The dry year created a new ecosystem."
In an invented coastal forest plot, rising seas raised soil salinity from 1 to 10 parts per thousand over 20 years. The plot had 60 trees in year 0, 35 in year 10 and 12 in year 20, while marsh grass cover rose from 0% to 30% to 70%. (a) What percentage of the trees were lost over 20 years? (b) Is this evidence about numbers, types of organisms or both? (c) Evaluate the claim "Sea level rise is producing a new ecosystem in this plot."
A student writes: "Claim: the reef became a new ecosystem. Evidence: live coral cover fell from 45% to 10%, seaweed cover rose from 20% to 65% and fish species fell from 120 to 85. Reasoning: fewer corals means less food and shelter." (a) Compute the percent change for each measurement. (b) Rate the claim, the evidence and the reasoning as strong, partial or weak, and explain. (c) What additional evidence would you ask for?
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Calculations
Correct means and percent changes, using the earlier value as the base
Correct method with one calculation error
Evaluating Evidence
Judges both numbers and types of organisms and names a specific strength or weakness (record length, baseline, comparison site)
Judges the evidence in general terms only
Evaluating Reasoning
Names the interactions that explain the pattern and says whether the claim follows from the evidence
Restates the claim without linking it to interactions or data
05
Quiz: 20 Questions
Interactive, with answers
Instructions
All data sets are invented. Percent changes use the earlier value as the base. Your score updates as you answer, and Reset quiz clears everything so you or your students can try again.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
Which statement best matches the claim that HS-LS2-6 asks students to evaluate?
Answer: C
This is the two-part claim in the standard. Choice A ignores natural changes such as floods and eruptions. Choice B ignores the evidence that ecosystems recover from modest changes. Choice D confuses "relatively consistent" with "exactly the same".
Question 2 of 20 · Multiple Choice
A pond survey counts 60, 64, 57, 61 and 58 green frogs in five years. What is the mean?
Answer: C
The sum is 300, and 300 ÷ 5 = 60. Choices A, B and D are single years (the fifth, the fourth and the second), not the mean. Choosing the largest value (choice D) is a frequent error when students guess instead of adding.
Question 3 of 20 · Multiple Choice
Which change is most likely to produce a new ecosystem rather than a short-term dip?
Answer: D
Stripping a hillside to bare rock removes the soil and nearly all the organisms, so the community that grows back can be very different. Choices A, B and C are modest changes after which ecosystems usually return to about the same numbers and types of organisms.
Question 4 of 20 · Multiple Choice
A student claims that a new hiking trail with moderate foot traffic did not change the types of organisms in a meadow. Which evidence would best test that claim?
Answer: A
The claim is about types of organisms, so the evidence must be species surveys that cover the time before and after the change. Choice B measures people, not the ecosystem. Choice C describes the trail, not the organisms. Choice D is a single moment with no baseline.
Question 5 of 20 · Multiple Choice
An invented count of beavers in a river valley fell from 250 to 215 after a trapping season. What is the percent change?
Answer: A
(215 - 250) ÷ 250 = -35 ÷ 250 = -0.14, a 14% decrease. Choice B divides by the new value (215) instead of the original. Choice C gives the change in beavers, not the percent. Choice D has the wrong sign.
Question 6 of 20 · Multiple Choice
Four invented five-year population records are shown. Which one best fits "relatively consistent numbers" in stable conditions?
Answer: B
Record B rises and falls but stays within 7% of its mean of 100, which is what interactions produce in stable conditions. Choice A grows every year and choice C falls every year, so neither stays in a range. Choice D swings far above and below its mean, so its numbers are not consistent even though it has no overall trend.
Question 7 of 20 · Multiple Choice
Counts of ground squirrels on a prairie stay within about 12% of their mean for ten years. Which reasoning best explains this pattern?
Answer: C
Predation and competition for food increase when ground squirrels are plentiful and decrease when they are scarce, pulling the population back toward the average. Choice A is not how reproduction works. Choice B ignores the interactions that the standard is about. Choice D is wrong because the counts come from the same prairie each year.
Question 8 of 20 · Multiple Choice
A state claims that a new fishing rule restored the trout in Lake A: trout counts rose 30% in the five years after the rule. Which added evidence would most strengthen the claim?
Answer: C
A comparison lake shows whether trout rose everywhere (for example, because of weather) or only where the rule applied. Choice A adds length but not a comparison. Choice B is opinion, not data.
Question 9 of 20 · Multiple Choice
A plot had 30 plant species before a disturbance. Afterward it had 29 species: 27 from the original list and 2 new ones. What percentage of the original species remained?
Answer: B
27 ÷ 30 = 0.90, so 90% of the original species remained. Choice A divides the new total (29) by 30 and hides the lost species. Choice C divides 27 by 29, the wrong base. Choice D is the share of the original species that were lost (3 of 30).
Question 10 of 20 · Multiple Choice
A student claims a meadow is stable because the same 12 plant species were found in each of the last 10 summers. No counts of any species are given. What is the main limitation of this evidence?
Answer: D
HS-LS2-6 is about both the numbers and the types of organisms. A steady species list supports the "types" half; counts or cover data are needed for the "numbers" half. Choice A is wrong because ten years is a useful record. Choice B reverses what the evidence shows.
Question 11 of 20 · Multiple Choice
Frog numbers in a wetland fell in the same years that a new road was built and a drought occurred. A student claims the road caused the decline. What is the best evaluation?
Answer: B
Two changes happened at once, so the timing alone cannot separate their effects. Choice A treats a correlation as proof. Choice C is an unsupported overgeneralization.
Question 12 of 20 · Multiple Choice
Which evidence best shows that a changing condition has produced a new ecosystem?
Answer: A
A new ecosystem means a lasting change in the kinds of organisms, especially the dominant ones. Choice B describes recovery from a modest change. Choice D describes the normal fluctuation of a stable ecosystem.
Question 13 of 20 · Multiple Choice
After a seasonal flood, the number of ground beetles in an invented floodplain fell by 40%, and one year later it was within 5% of the pre-flood count, with the same beetle species. What do these data best support?
Answer: D
A large short-term drop followed by a return to the earlier numbers and the same species fits a modest change. Choices A and B ignore the recovery. Choice C contradicts the one-year data.
Question 14 of 20 · Multiple Choice
Counts of a lizard species over six years are 88, 95, 102, 110, 97 and 108. In how many years is the count within 10% of the mean?
Answer: C
The mean is 600 ÷ 6 = 100, so the range is 90 to 110. Only 88 falls outside it, so 5 of the 6 years are within 10%. Choice B treats 110 as outside the range. Choice A misses that 88 is 12% below the mean.
Question 15 of 20 · Short Answer
A student writes: "Claim: hunting ruined the forest. Evidence: there were 300 deer before the hunting season and 270 after the first year." Evaluate the claim, the evidence and the reasoning.
The deer count fell by 10% ((270 - 300) ÷ 300). The claim is not supported: one year of data cannot show a lasting change, and deer numbers alone say nothing about the other types of organisms. The reasoning is missing: the student does not explain how fewer deer would change plants, predators or other species. Better evidence would be several years of deer counts and plant and animal surveys before and during hunting.
Question 16 of 20 · Short Answer
An invented plot had 45 plant species before a volcanic eruption. Twenty years later it had 36 species, 18 of them from the original list. What percentage of the original species are present, how many species are new, and does this support a new ecosystem?
Original species present: 18 ÷ 45 = 40%. New species: 36 - 18 = 18, half of the plants now there. Yes: the number of species has partly recovered, but the types have changed a lot, which supports a new ecosystem.
Question 17 of 20 · Short Answer
A town claims that the river through its park "always bounces back" from spring floods. Plan the evidence you would collect to evaluate this claim.
Collect data for several years before and after floods: counts of key organisms (for example, insect families, fish and streamside plants) and species lists, at the same sites and times of year. Include a comparison stretch of river that floods less, and record flood size. The claim is supported if numbers and types return to their pre-flood range within a set time after each flood.
Question 18 of 20 · Short Answer
Explain, using two kinds of interactions, how an ecosystem can keep the numbers of a prey species relatively consistent. Use an example that is not on this page.
Example: snowshoe hares in a northern forest. Predation: when hares are plentiful, lynx and owls catch more of them, which pulls the population down. Competition for food: when hares are crowded, they eat the shrubs faster than they regrow, so fewer young survive. When hares are scarce, both pressures ease and the population grows again. (Hare numbers do cycle over about a decade, so a record of many years is needed to see the range.)
Question 19 of 20 · Short Answer
Classify each change as modest or extreme and predict whether the ecosystem is likely to return to about the same numbers and types of organisms: (a) a mild winter; (b) a river valley permanently flooded behind a new dam; (c) a late frost that kills the wildflower blooms on a hillside for one spring; (d) a glacier melting away and leaving bare rock.
(a) Modest, likely to return. (b) Extreme: a river becomes a lake, so a new ecosystem forms. (c) Modest, likely to return: the plants survive and bloom again the next year, though insects that feed on the flowers may dip for a season. (d) Extreme: new organisms colonize the bare rock, so a new ecosystem forms.
Question 20 of 20 · Short Answer
Frog counts in a wetland were 40, 44, 38, 42 and 41 for five years. After the wetland was drained, counts were 22, 15, 9, 6 and 3. Find both means and the percent change, and name one more kind of evidence you would need to claim the wetland has become a new ecosystem.
Means: 41 before and 11 after (55 ÷ 5). Percent change: (11 - 41) ÷ 41 = -73.2%. Frog numbers alone describe one population; to claim a new ecosystem you also need data on which kinds of organisms now live there, showing that the types have changed (for example, wetland plants replaced by dry-ground plants).
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-LS2-6 mean?
HS-LS2-6 asks students to evaluate the claims, evidence and reasoning behind the idea that ecosystem interactions keep the numbers and types of organisms relatively consistent under stable conditions, while changing conditions can lead to a new ecosystem. The practice is evaluation: students judge arguments and data, not only describe ecosystems. The code means High School, Life Science, core idea 2 (Ecosystems: Interactions, Energy, and Dynamics), performance expectation 6.
Does HS-LS2-6 have an assessment boundary?
No. HS-LS2-6 has no official Assessment Boundary, only a Clarification Statement. The Clarification Statement gives examples of modest changes (moderate hunting, a seasonal flood) and extreme changes (a volcanic eruption, sea level rise), and this lesson uses all four.
What is the difference between a modest change and an extreme change?
After a modest change, an ecosystem usually returns to about the same numbers and types of organisms, sometimes at a slightly different level. An extreme change can remove the old community or change the physical conditions so much that a different set of organisms takes over. Data over several years are what tell the two apart.
Does a stable ecosystem mean populations never change?
No. In a stable ecosystem, populations rise and fall from year to year, but they stay within a range around an average, and the same types of organisms remain. Predation, competition, disease and limited resources pull numbers back toward that range.
How do students evaluate claims, evidence and reasoning in ecology?
For the claim, they check exactly what is said to be stable or new. For the evidence, they ask how many years were measured, whether there is a baseline and a comparison site, and whether both numbers and types of organisms were measured. For the reasoning, they check whether the argument names the interactions that explain the pattern.
What math do students need for HS-LS2-6?
Means, ranges and percent change are enough for most data sets, all of which fit in an Algebra I course. Students should use the earlier value as the base for percent change and compare changes with the normal range of year-to-year variation.
Is HS-LS2-6 taught in Biology or Environmental Science?
It is usually taught in the ecology unit of high school Biology and also fits Environmental Science. It pairs well with HS-LS2-2 on biodiversity and HS-LS2-7 on reducing human impacts.
What are good real-world examples for HS-LS2-6?
Long-term monitoring of a local park or stream, recovery of plant communities after floods, regulated hunting or fishing, the plant communities that develop on new volcanic rock, and coastal marshes and forests changing as salt water moves inland. When using real cases, use published data and note that scientists sometimes disagree about the causes.
Can students collect their own data for HS-LS2-6?
Yes. A schoolyard quadrat survey repeated each year builds a real baseline. Choose plot locations at random, check the area for hazards such as poison ivy and stinging insects, use gloves and wash hands afterward. One class period gives a snapshot; the value grows as later classes add years.
What mistakes do students make with ecosystem stability claims?
Many students treat any drop in a population as a new ecosystem, treat "stable" as "unchanging", rely on one or two years of data, or accept that two changes happening together proves one caused the other. Asking "numbers, types or both?" and "compared with what?" addresses most of these.
07
Related Standards
6 standards
These standards connect to HS-LS2-6: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-LS2-4Prerequisite
Argue from evidence that changes to parts of an ecosystem affect populations
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