MS-LS2-4: Arguing From Evidence That Ecosystem Changes Affect Populations
In plain English: MS-LS2-4 is the NGSS middle school performance expectation that asks students to construct an argument, supported by data, that changes to the physical or biological parts of an ecosystem affect populations. Students read patterns in population data, make claims the data can support, and judge how strong the evidence is. It is usually taught in middle school life science.
Construct an argument supported by empirical evidence that changes to physical or biological components of an ecosystem affect populations.
Clarification Statement: Emphasis is on recognizing patterns in data and making warranted inferences about changes in populations, and on evaluating empirical evidence supporting arguments about changes to ecosystems.
Next Generation Science Standards · Disciplinary Core Idea: Ecosystems: Interactions, Energy, and Dynamics · Official standard
Students construct arguments, backed by data, that a change to an ecosystem changed a population. A population is all the members of one species living in an area. The parts of an ecosystem are either physical (nonliving), such as water temperature, rainfall, soil, light or the shape of a river, or biological (living), such as predators, diseases, food plants or a newly arrived species. Empirical evidence is evidence from measurements and observations, not from opinions. Students learn to write an argument with three parts: a claim (what changed and why), evidence (specific data) and reasoning (the science idea that links the evidence to the claim).
The NGSS Clarification Statement says: "Emphasis is on recognizing patterns in data and making warranted inferences about changes in populations, and on evaluating empirical evidence supporting arguments about changes to ecosystems." A warranted inference is a conclusion that the data really support, no more and no less. This performance expectation has no Assessment Boundary. Students practice the moves that make evidence strong: before-and-after data, a comparison site that did not change, several samples or years, and a check for other explanations. All data sets are invented for teaching and labeled as invented; the background facts about real species (for example, that trout need cold water) are real.
Learning Objectives
By the end of this lesson, students will be able to:
Identify whether a change to an ecosystem is to a physical or a biological component
Describe patterns in population data, using means, differences and percent changes, before and after a change
Construct an argument with a claim, evidence and reasoning that a change to an ecosystem affected one or more populations
Evaluate the strength of evidence, looking for comparison sites, enough samples and other explanations, and make only warranted inferences
Prior Knowledge Required
Students should already be comfortable with:
How a change in a habitat can change which plants and animals live there 3-LS4-4
Arguing that in a habitat some organisms survive well, some less well and some not at all 3-LS4-3
Write two statements on the board: "I think the frogs left because of the new road." and "Frog counts at the pond fell from 40 to 12 after the road opened, while a pond with no road stayed near 40."
Warm-Up Prompt
"Which statement would convince a town council, and why? What is the difference between an opinion and evidence? Write one more piece of data that would make the second statement even stronger."
Students share their extra data ideas, such as more years of counts or more ponds. Tell them that today's goal is to build arguments like the second statement and to judge how strong they are.
Direct Instruction15-20 minutes
Building an argument from evidence. Populations change when the ecosystem around them changes. A change to a physical component (warmer water, a flood, a dam) or to a biological component (a new predator, a disease, a lost food plant) can make a population grow or shrink, and often it affects several populations at once. To argue that a change affected a population, look for these features of strong evidence:
Before and after: the population was measured before the change and after it.
A comparison: a similar place that did not change, measured over the same years. If both places changed the same way, something else is probably the cause.
Enough data: several samples or years, so one unusual count does not mislead.
A reason: a science idea that explains how the change would affect the population.
A pattern that shows two things changing together does not by itself prove that one caused the other. Warranted inferences say only what the evidence supports. Use Diagram 1 with the first example and Diagram 2 with the second.
Physical change: warmer water in a stream (Diagram 1)
Invented data. Trout, fish that need cold water, were counted each summer from 2018 to 2025 in two reaches (stretches) of one stream. In the winter before the 2021 survey, the trees beside reach A were cut down; the trees beside reach B were left. Reach A trout per 100 m: 46, 50, 48, 31, 24, 21, 19, 20. Reach B: 44, 47, 47, 46, 43, 47, 44, 45. Summer high water temperature in reach A rose from 16 °C to 22 °C; reach B stayed at 16 °C.
Result: Reach A mean: 48 before (2018-2020) and (31 + 24 + 21 + 19 + 20) ÷ 5 = 23 after, a drop of 25 trout, or about 52%. Reach B mean: 46 before and 45 after. Claim: removing the shade warmed reach A, and the warmer water lowered its trout population. Evidence: the drop came right after the cutting, the water warmed by 6 °C, and reach B, with no change, stayed steady. Reasoning: trout need cold water, and water in full sun heats up.
Biological change: an invasive shrub (Diagram 2)
Invented data from 8 meadow plots. An invasive shrub (a plant brought from another continent that spreads quickly) covers 5% to 85% of the ground. Native bee visits to flowers in 10 minutes, in order of shrub cover: 34, 30, 27, 20, 18, 12, 7, 4. In a follow-up test, the shrub was cleared from some plots: bee visits rose from 8 to 25 in two years, while uncleared plots went from 7 to 6.
Result: Pattern: the more shrub cover, the fewer bee visits, from 34 at 5% cover to 4 at 85%. The pattern alone does not prove cause, because the plots could differ in other ways. The clearing test makes the argument stronger: removing the shrub was followed by 17 more visits, while uncleared plots stayed low. Reasoning: the shrub crowds out the native flowers that bees feed on.
Biological change spreads to another population
Invented data from one valley. A disease reached the valley's rabbits late in 2020. Rabbits counted: 2019: 820, 2020: 790, 2021: 210, 2022: 260. Pairs of hawks that eat rabbits nesting in the valley: 14, 15, 13, 8.
Result: Rabbits fell by 790 - 210 = 580, about 73%, in one year. Hawk pairs fell from 13 to 8 a year later. Claim: the disease lowered the rabbit population, and the loss of prey then lowered the hawk population. Evidence: the timing, with the hawks falling after the rabbits. A comparison valley without the disease would make the argument stronger.
Evaluating two arguments about a drought
Invented data about dragonfly young (larvae) in ponds during a drought. Argument 1: "The drought lowered dragonflies: in Cedar Pond, I counted 18 larvae last year and 7 this year." Argument 2: "The drought lowered dragonflies: in 5 ponds that shrank, the mean fell from 22 to 9 larvae per sample, while in 5 spring-fed ponds that kept their water, it went from 21 to 20."
Result: Both claims are the same, but Argument 2 is stronger: it uses 5 ponds instead of 1, and it compares ponds that shrank with ponds that did not. A drop of 13 in shrinking ponds against a drop of 1 in spring-fed ponds points to the water loss, not to something that affected every pond.
Physical change and a fix: a dam and a fish ladder
Invented data for a fish that swims up a river each spring to lay eggs. Counted at a station upstream of where a dam was later built: 5,200, 4,800 and 5,000 in the three springs before the dam; 300, 120 and 40 in the three springs after it was built; 1,600 and 2,100 in the two springs after a fish ladder (a set of water-filled steps that fish can swim up) was added. Counts below the dam stayed near 5,000 the whole time.
Result: Before: (5,200 + 4,800 + 5,000) ÷ 3 = 5,000. After the dam the count fell to 40 in three years. After the ladder, 2,100 ÷ 5,000 = 42% of the old number returned. Claim: the dam blocked the fish from reaching the upstream river, and the ladder let part of the population return. The steady counts below the dam rule out a drop in the whole population.
After each example, ask: "What new data would weaken this argument?" For the invasive shrub, finding that cleared plots stayed just as low as uncleared plots would weaken it.
Guided Practice10-15 minutes
Pairs analyze invented data from a forest where a strong windstorm knocked down most of the trees in some plots. The storm opened the forest floor to sunlight and dried out the ground.
Guided practice data: a windstorm in a forest (invented means of 4 plots in each group)
Plots
Butterflies seen per 30-minute walk, before
Butterflies, two years after
Salamanders under 10 boards, before
Salamanders, two years after
Trees blown down
6
19
14
5
Trees still standing
5
6
15
14
Find the change in each population in each group of plots. Which populations changed a lot, and which stayed about the same?
Write a claim about how the windstorm affected the two populations. Notice that the same change can make one population grow and another shrink.
Write your evidence, using the comparison with the standing plots. Then write reasoning: why would more sunlight help butterflies, and why would drier ground hurt salamanders, which breathe through moist skin?
Name one other explanation for the data, and one more measurement that could rule it out.
Independent Practice10-15 minutes
Each student writes an argument. In many northern forests of North America, earthworms are not native. Earthworms brought in with fishing bait and garden soil eat the thick layer of dead leaves on the forest floor, where wildflower seeds sprout and salamanders hide.
Independent practice data: forest plots with and without earthworms (invented means of 6 plots)
Measurement
Plots with earthworms
Plots without earthworms
Depth of dead leaves on the ground
1 cm
6 cm
Wildflower stems per plot
12
40
Salamanders under 10 boards
3
9
Students write a claim, at least two pieces of evidence with numbers, and reasoning that connects the earthworms to both the wildflowers and the salamanders through the leaf layer. Then they write one sentence that evaluates the evidence: what is missing that would make the argument stronger? A strong answer notes that the data compare places, not one place before and after, so the plots might differ in other ways, such as soil or tree type.
Closure5 minutes
Exit ticket: "Lizards were counted on 3 islands that a hurricane hit (mean 120 before, 45 after) and on 3 islands it missed (118 before, 116 after). Write a claim and name the single strongest piece of evidence for it." (Claim: the hurricane lowered the lizard populations. Strongest evidence: the islands the storm missed stayed steady, so the drop on the hit islands was not caused by something that affected all islands.) Return to the warm-up and have students label the claim, evidence and reasoning in the second statement.
Differentiation Strategies
For Struggling Students
Provide an argument frame: "Claim: ___ changed the ___ population. Evidence: before, ___; after, ___; at the comparison site, ___. Reasoning: this happened because ___."
Give a checklist with four boxes (before and after, comparison, enough data, reason) to tick for each argument
Let students compute changes as differences before moving to percents
For Advanced Students
Ask students to find a case where one change affected three or more populations, and draw the chain of effects
Have students graph the Activity 2 class data with the mean and the range for each salt level and judge whether the differences are larger than the spread
Ask students to write the strongest possible counterargument to Example 2 and say what data would settle the disagreement
Assessment Guidance
What to Look For
Check that every claim names the change, the population and the direction of the effect, and that the evidence uses specific numbers from the data. Look for students who use a comparison site or several samples to support a cause, and who say what the data cannot show. Watch for overreaching claims ("the storm wiped out the crabs forever") and for evidence that is an opinion or a single count. Strong reasoning names a science idea, such as what the organism needs, that links the change to the population.
02
Classroom Activities
3 Activities
1
Data Detective Stations: Four Ecosystem Changes
20 minGroups of 3-4
Groups rotate through four stations, about 5 minutes each. Each card describes one change to an ecosystem with invented data. At each station the group writes a claim, the best piece of evidence and the reasoning, and marks the change as physical or biological.
Station Cards (invented data)
Station A, beavers move in: beavers dam a creek, and a pond floods part of a meadow. Frogs heard calling at night: 6 and 5 in the two years before, 38 and 42 in the two years after. Grasshoppers per net sweep in the meadow: 24 and 22 before, 6 and 5 after.
Station B, a disease in bats: bats counted in a cave each winter, 2016-2020: 3,400, 3,300, 1,100, 400, 350, with the disease first found in 2018. A nearby cave where the disease was not found: 2,100, 2,200, 2,150, 2,050, 2,100.
Station C, a heat wave in a bay: in a shallow bay the summer high water temperature rose from 24 °C to 29 °C in a heat-wave year; eelgrass (an underwater plant) cover fell from 60% to 15%, and young scallops, which attach to eelgrass, fell from 12 to 2 per m². In a deeper, cooler bay (25 °C): eelgrass 55% to 50%, young scallops 10 to 9.
Station D, goats removed from an island: goats that ate the shrubs were removed in 2018. Shrub cover rose from 10% to 45% by 2023. Seabird nesting burrows per hectare, which the birds dig under shrubs: 40 in 2016, 38 in 2017, 70 in 2020, 110 in 2023.
Procedure
At each station, mark the change as physical or biological. Some changes start as one and cause the other.
Write a claim about which populations changed and in which direction.
Choose the single best piece of evidence and explain why it is the best.
Rate the evidence from 1 (weak) to 3 (strong): does the card have before-and-after data, a comparison place and more than one year?
Discussion Questions
At Station A, beavers are a biological change, but they also change the physical ecosystem. How did that one change make one population grow and another shrink?
Stations B and C both have a comparison place. How does it change your rating?
Station D has no comparison island. What data would you add to make the argument stronger?
Modification for Distance Learning
Post the four cards as slides. Students work in breakout rooms and type their claim, evidence and rating into a shared table.
2
Salty Soil Seedling Test
15 min to set up, 10 min after 7 daysGroups of 3
Groups test how a physical change, salt in the soil (as happens beside roads that are salted in winter), affects a population of mustard seedlings. They plant seeds, water them with different salt levels and count the seedlings alive after 7 days.
Procedure
Fill 12 cups with potting soil and plant 20 untreated mustard seeds in each, about 0.5 cm deep. Label 3 cups for each salt level: 0, 2, 5 and 10 g of table salt per liter of water.
Mix each salt solution in its own labeled 1 L bottle. Water every cup with the same amount, 30 mL, every other day, and keep all cups in the same light and temperature.
After 7 days, count the living seedlings in each cup and find the mean for each salt level.
Safety: use only table salt and untreated seeds, never road salt or seeds coated with chemicals; do not eat seeds or seedlings; wipe up spills; wash hands after handling soil.
Sample Data (invented)
Living seedlings out of 20 in the three cups at each salt level: 0 g/L: 18, 17, 19; 2 g/L: 15, 16, 14; 5 g/L: 9, 10, 8; 10 g/L: 2, 3, 1.
Discussion Questions
The means are 18, 15, 9 and 2 seedlings. Describe the pattern in one sentence.
Why does the test use 3 cups at each salt level instead of 1?
Write an argument, with claim, evidence and reasoning, about what salting a road might do to the plant populations beside it. What can this classroom test not tell you about a real roadside?
Modification for Distance Learning
Students run the test at home with an adult using two cups (plain water and 5 g/L), or graph the sample data and write the argument.
3
Argument Gallery: How Strong Is the Evidence?
15 minPairs
Four argument cards hang around the room. Pairs read each one, score its evidence with a checklist and place a sticky dot on a scale from weak to strong. The class then compares scores and rewrites the weakest argument.
The Four Argument Cards (invented data)
Card 1: "A new road made the frogs leave Mill Pond. I counted 30 frogs one night before the road and 12 one night after."
Card 2: "Removing nonnative rats from Gull Island let terns (seabirds) nest there again. Tern nests on Gull Island: 10, 12, 9 and 11 in the four years before the rats were removed, then 25, 34 and 41. Nests on a nearby island that still has rats: 11, 10, 12, 9, 11, 10 and 12 over the same seven years."
Card 3: "The cold winter killed most of the deer. I saw fewer deer this spring than last spring."
Card 4: "An insect pest that killed trees made woodpeckers increase. Dead trees per hectare rose from 5 to 60 in two years, and woodpeckers seen per hour rose from 3 to 9."
Evidence Checklist
Is the evidence measured data, not an opinion or a feeling?
Are there data from before and after the change?
Is there a comparison place that did not change?
Are there several samples or years?
Does the reasoning explain how the change would affect the population?
Discussion Questions
Card 2 meets every item on the checklist except one. Which one is missing, and how would you add it?
Card 4 has numbers but no comparison place. What other explanation could account for more woodpeckers?
Rewrite Card 1 or Card 3 so that it would score as strong. What data would you need to collect?
Challenge Variation
Pairs write a fifth card that looks strong but has a hidden flaw, such as a comparison place that also changed, and trade it with another pair to find the flaw.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: Trout in Two Reaches of One Stream
Invented summer counts, drawn to scale. Trout in reach A fell after the streamside trees were cut and the water warmed, while trout in reach B, where the trees were left, stayed between 43 and 47. The comparison reach is what makes the argument strong.
Diagram 2: Invasive Shrub Cover and Native Bee Visits
Invented data from 8 meadow plots, drawn to scale. Plots with more ground covered by the invasive shrub had fewer native bee visits. The pattern supports an argument that the shrub lowers the bee population, but by itself it does not prove the shrub is the cause.
04
Homework Assignment
~30 min
MS-LS2-4 Homework: Arguing From Evidence About Ecosystem Changes
Directions: All data sets are invented for practice. Show each calculation. Every argument needs a claim, evidence with numbers and reasoning. When asked to evaluate evidence, say what makes it strong or weak.
Part 1: Physical and Biological Changes (Problems 1-3)
Mud washed into Lake Ross from a construction site. Water clarity (how deep a white disk can still be seen) fell from 3.0 m to 0.6 m, underwater plant cover fell from 40% to 14%, and young bluegill (a fish that hides in underwater plants) per net fell from 30 to 9. In nearby Lake Hart, with no construction, clarity went from 2.8 m to 2.9 m and young bluegill from 28 to 27. (a) Find the percent decrease in clarity, plant cover and young bluegill in Lake Ross. (b) Is the mud a physical or biological change? Write an argument about how it affected the bluegill. (c) Which piece of evidence makes your argument strongest, and why?
Mosquitofish, small fish released in some ponds to eat mosquito larvae, also eat tadpoles. In 6 ponds with mosquitofish, tadpoles averaged 4 per net sweep; in 6 ponds without them, 22. In two ponds where the mosquitofish were removed, tadpoles rose from 3 to 18 per sweep the next year. (a) How many times as many tadpoles were in the ponds without mosquitofish? (b) How many times as many tadpoles were there after the removal? (c) Write an argument and explain which evidence is most convincing.
Two students argue about why turtles declined in Willow Marsh. Student A: "Turtles declined because of the new hiking trail. I saw 9 turtles on one visit before the trail and 4 on one visit after." Student B: "Turtles declined because raccoons, which eat turtle eggs, increased. Over 5 years, raccoon tracks per survey rose from 3 to 15, and the share of turtle nests dug up rose from 20% to 80%. In a marsh where raccoons were kept out by fences, nests dug up stayed near 15%." (a) Use the evidence checklist to evaluate each argument. (b) Which is stronger, and why? (c) What one piece of data would most improve the weaker argument?
Part 2: Chains of Effects and Planning Evidence (Problems 4-6)
A heat wave struck a rocky shore during low tides. On a sunny stretch, mussel cover fell from 70% to 15% and barnacle cover rose from 10% to 45% over the next two years. On a shaded stretch, mussels went from 68% to 65% and barnacles from 12% to 13%. (a) Find the change in cover for each population on each stretch. (b) Write an argument about how the heat wave affected the two populations. (c) Whelks are snails that eat mussels. Predict what will happen to the whelks on the sunny stretch, and explain.
An insect pest killed most of the hemlock trees on a hillside. A warbler that nests only in hemlocks fell from 30 pairs to 6 pairs, while woodpeckers, which feed on insects in dead wood, rose from 4 to 11 birds. (a) Find the percent change for each bird population. (b) Write an argument that explains how one change affected the two populations in opposite directions. (c) What comparison would make the argument stronger?
A town claims: "Noise from the new highway lowers the number of songbirds nesting nearby." Plan the evidence you would collect to test the claim. (a) What would you measure, where and for how long? (b) What comparison would you use? (c) Describe one result that would support the claim and one that would weaken it.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Calculations
Means, differences, percent changes and times-as-many comparisons are correct
Correct method with one calculation error
Argument
Claim names the change, the population and the direction; evidence uses specific numbers; reasoning gives a science idea that links them
Claim and evidence present, but the reasoning is missing or does not connect them
Evaluating Evidence
Names comparison sites, number of samples and other explanations, and makes only warranted inferences
Names one strength or weakness of the evidence
05
Quiz: 20 Questions
Interactive, with answers
Instructions
All data sets are invented, and each question gives you the data you need. 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 of these is a change to a physical (nonliving) component of an ecosystem?
Answer: C
A flood and the mud it leaves are nonliving parts of the ecosystem. Choices A, B and D are all biological changes: a disease, a plant and a predator are living things. Each of the four could affect populations, but only the flood is physical.
Question 2 of 20 · Multiple Choice
Native minnows in a lake averaged 50 per net before a nonnative fish arrived and 32 per net after. By what percent did the minnow catch decrease?
Answer: B
The drop is 50 - 32 = 18, and 18 ÷ 50 = 0.36, a 36% decrease. Choice A reports the drop of 18 minnows as a percent. Choice C is the share that remained, 32 ÷ 50. Choice D divides by the new value: 18 ÷ 32 ≈ 0.56.
Question 3 of 20 · Multiple Choice
A student argues that a new road lowered the number of toads in a valley. Which evidence would best support the argument?
Answer: D
The far ponds act as a comparison: toads fell only where the road could affect them, which points to the road as the cause. Choice B is an impression, not measured data. Choice C has no before data to compare with. Choice A describes the road, not the toads.
Question 4 of 20 · Multiple Choice
Foxes arrived on Island X in year 1. Ground-nesting bird nests in years 1-4: 80, 52, 30, 18. On fox-free Island Y over the same years: 76, 79, 74, 78. Which inference is warranted?
Answer: A
Nests fell from 80 to 18 on the island with foxes while Island Y stayed between 74 and 79, so the foxes are the most likely cause. Choice B misreads Island Y, which stayed steady. Choice D is ruled out by the steady counts on Y. Choice C goes far beyond what data from two islands can support.
Question 5 of 20 · Multiple Choice
Salamanders were counted under boards in 4 forest plots before logging (12, 9, 11, 8) and after logging (4, 6, 3, 3). By how many salamanders per plot did the mean fall?
Answer: C
Mean before: 40 ÷ 4 = 10. Mean after: 16 ÷ 4 = 4. The mean fell by 10 - 4 = 6. Choice A is the mean after, and choice D is the mean before. Choice B is the drop in the total count, 40 - 16, not per plot.
Question 6 of 20 · Multiple Choice
A town found that frog numbers fell during the same years that many new houses were built. What should a careful scientist conclude?
Answer: D
Two things changing at the same time is a pattern that fits the argument, but it does not prove cause; something else that changed in those years, such as a drought, could explain it. Choice A claims more than the data show. Choice C turns one town into a rule for everywhere. Choice B ignores a pattern that is worth testing.
Question 7 of 20 · Multiple Choice
A disease kills most of the ground squirrels in a grassland. Badgers there eat mainly ground squirrels. Which population is most likely to decrease next?
Answer: B
The badgers lose much of their food, so their population is likely to fall after the squirrels fall. Choice A has the direction backwards: with fewer squirrels eating them, grasses and seeds are more likely to increase. Choices C and D name populations with no clear link to the squirrels.
Question 8 of 20 · Multiple Choice
Deer were fenced out of some forest plots. Tree seedlings per plot went from 6 to 27 inside the fences, while unfenced plots stayed near 6. How many times as many seedlings grew inside the fences?
Answer: D
27 ÷ 6 = 4.5, so there were 4.5 times as many seedlings. Choice A is the difference, 27 - 6, not a times-as-many comparison. Choice B divides the wrong way: 6 ÷ 27 ≈ 0.22. Choice C adds the counts.
Question 9 of 20 · Multiple Choice
Moths caught in light traps averaged 50 per night in the three summers before a wildfire and 20 per night in the summer after it. Which claim do the data support?
Answer: A
Moths fell from 50 to 20 per night right after the fire, so the data support a drop for that summer. Choice B is wrong because moths were still caught. Choice C predicts the future, which one summer of data cannot show. Choice D contradicts the data.
Question 10 of 20 · Multiple Choice
Students want evidence that a new trail lowered the number of wildflowers. Which data set would give the strongest evidence?
Answer: C
Many plots, several years and a comparison far from the trail let students see whether the change happened only near the trail. Choices A and B have no data from before or from a comparison. Choice D has several years but only one plot and no comparison place.
Question 11 of 20 · Multiple Choice
A scientist argues that warmer water lowered the trout in Creek 1. Which new finding would most weaken the argument?
Answer: B
If trout fell just as much in a creek that stayed cold, something other than warm water is probably the cause. Choices A and C support the argument. Choice D only repeats the pattern the argument explains.
Question 12 of 20 · Multiple Choice
A storm hit a barrier island. Beach mice were counted at 400 before the storm, 80 just after it and 300 two years later. What percent of the pre-storm number had returned two years later?
Answer: C
300 ÷ 400 = 0.75, so 75% of the pre-storm number was back. Choice A is the number just after the storm, 80 ÷ 400. Choice B is the share still missing, 100% - 75%. Choice D divides 300 by the 80 mice just after the storm.
Question 13 of 20 · Multiple Choice
An invasive vine is growing over the shrubs where a songbird builds its nests. Which data would be empirical evidence that the vine affected the songbird population?
Answer: A
Empirical evidence is measured data about the population itself, and a comparison of plots with and without the vine tests the argument. Choice B shows the vine but says nothing about the birds. Choice C is an opinion. Choice D is a fact about the vine, not about its effect.
Question 14 of 20 · Multiple Choice
A student's argument has three sentences. Which one is the reasoning?
Answer: B
Reasoning is the science idea that connects the evidence to the claim: hermit crabs need empty snail shells, so fewer snails leave fewer shells for them to live in. Choice C is the claim. Choices A and D are evidence, because they give the measured data.
Question 15 of 20 · Short Answer
Cottonwood trees along a river sprout on wet sandbars left by spring floods. Seedlings per 100 m² in three years with spring floods, before a dam was built: 45, 52, 38. In three years after the dam stopped the floods: 3, 1, 2 (invented data). Find both means and write an argument with a claim, evidence and reasoning.
Means: 45 before and 2 after (135 ÷ 3 and 6 ÷ 3). Claim: by stopping the spring floods, the dam lowered the number of new cottonwoods. Evidence: seedlings fell from a mean of 45 to 2 per 100 m² once the floods stopped. Reasoning: cottonwood seeds need the wet, bare sandbars that floods leave, so without floods few seeds can sprout. A comparison river without a dam would make the argument stronger.
Question 16 of 20 · Short Answer
House finches at a group of bird feeders fell from a mean of 60 per count to 24 per count in two years after an eye disease was first seen in the finches (invented data). Find the percent decrease. Then name two more pieces of evidence that would make an argument that the disease caused the decline stronger.
(60 - 24) ÷ 60 = 36 ÷ 60 = 60% decrease. Stronger evidence: (1) a comparison, such as finch counts at feeders where the disease was not found, staying steady; (2) the share of finches with the disease rising as the counts fell. Counts from more years before the disease would also help.
Question 17 of 20 · Short Answer
Evaluate this argument: "The new wind farm caused fewer hawks. I counted 8 hawks at the wind farm last fall and 5 this fall." Name two weaknesses and describe better evidence.
Weaknesses: only one count each fall, so the difference of 3 hawks could be chance or weather; no comparison place without turbines, so a drop everywhere could not be ruled out. Better evidence: hawk counts on many days for several falls before and after the turbines were built, at the wind farm and at a similar site with no turbines.
Question 18 of 20 · Short Answer
Plan an investigation to test the claim that an invasive snail lowers the number of native snails in streams. Describe what you would measure, where, and what result would support the claim.
Measure native snails per sample (for example, per rock or per square of stream bottom) in several streams with and without the invasive snail, and if possible in the same streams before and after it arrives, over several years. Keep the kinds of streams similar. The claim is supported if native snails fall where the invader arrives but stay steady in streams it has not reached.
Question 19 of 20 · Short Answer
In 2022 Lake A only warmed, Lake B only got an invasive fish, and Lake C both warmed and got the invasive fish. Native fish per net, 2021 to 2024 (invented data): Lake A 40 to 36, Lake B 42 to 20, Lake C 41 to 15. Find the drop in each lake and argue which change had the larger effect.
Drops: Lake A 4, Lake B 22, Lake C 26. Claim: the invasive fish had a much larger effect than the warming. Evidence: the lake with only the invader lost 22 fish per net, while the lake that only warmed lost 4; the lake with both lost 26, about the sum of the two. Reasoning: the invader eats or competes with the native fish, while a small rise in temperature stresses them less.
Question 20 of 20 · Short Answer
As the Arctic warms, shrubs are spreading across parts of the tundra and shading the ground. In one area, lichen cover fell from 30% to 18% over 10 years (invented data). Caribou depend on lichens for food in winter. Write an argument that predicts how the caribou population could change, and say what evidence you would need to support it.
Claim: the caribou population is likely to decline, or the caribou will move elsewhere in winter. Evidence: lichen cover fell by 12 percentage points, or 40% of what was there, in 10 years. Reasoning: caribou rely on lichens in winter, so less lichen means less winter food. Needed evidence: caribou counts and body condition over the same years, compared with an area where shrubs have not spread.
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06
Frequently Asked Questions
10 Questions
What does MS-LS2-4 mean?
MS-LS2-4 asks middle school students to construct an argument, supported by data, that changes to the physical or biological parts of an ecosystem affect populations. The code stands for Middle School, Life Science, core idea 2 (Ecosystems: Interactions, Energy, and Dynamics), performance expectation 4.
What is empirical evidence in MS-LS2-4?
Empirical evidence is evidence from measurements and observations, such as population counts, temperatures or percent cover. A feeling that "there seem to be fewer birds" is not empirical evidence; counts of nests over several years are.
What is the difference between a physical and a biological change?
A physical change affects a nonliving part of the ecosystem, such as water temperature, rainfall, soil, light or a river's shape. A biological change affects a living part, such as a new predator, a disease or an invasive plant. One change can lead to the other: beavers are living, but their dams change the water.
What makes evidence strong?
Strong evidence has data from before and after the change, a comparison place that did not change, several samples or years, and a reason that explains the effect. Evidence that has only one count, or no comparison, can still support a claim, but more weakly.
What is a warranted inference?
A warranted inference is a conclusion that the data really support. If a pond's snails fell after one very cold winter, "the cold winter lowered snail numbers that spring" is warranted, but "the snails are gone for good" is not, because one spring of data cannot show the future.
Does a pattern in data prove that one change caused another?
No. Two things changing together fits a cause-and-effect argument but does not prove it, because something else could have changed at the same time. Comparison places, before-and-after data and tests such as removing an invasive species make the argument much stronger.
Is there an assessment boundary for MS-LS2-4?
No. The performance expectation has no Assessment Boundary. The Clarification Statement puts the emphasis on recognizing patterns in data, making warranted inferences about populations and evaluating the evidence behind arguments about ecosystem changes.
How is MS-LS2-4 different from MS-LS2-1?
MS-LS2-1 asks students to analyze data on how the amount of a resource, such as food or water, affects organisms and populations. MS-LS2-4 is broader and centers on argument: any change to a physical or biological part of an ecosystem, and how well the evidence supports a claim about it.
What are common mistakes students make?
Students often give an opinion as evidence, use one count before and one after with no comparison, or claim more than the data show. Another common mistake is to forget that one change can make one population grow while another shrinks.
What comes after MS-LS2-4?
In high school, HS-LS2-6 asks students to evaluate claims that ecosystems keep relatively steady numbers of organisms in stable conditions but may change greatly when conditions change, and HS-LS2-2 uses math to support and revise explanations about biodiversity and populations.
07
Related Standards
6 standards
These standards connect to MS-LS2-4: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
3-LS4-4Prerequisite
Judge a solution to a problem caused when the environment changes and its organisms change
Lesson coming soon
3-LS4-3Prerequisite
Argue that in a habitat some organisms survive well, some less well and some not at all
Lesson coming soon
Alongside
MS-LS2-1Parallel
Analyze data on how resource availability affects organisms and populations
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