HS-LS4-5: Evaluating Evidence on Environmental Change and Species
In plain English: HS-LS4-5 is the NGSS high school performance expectation that asks students to evaluate the evidence for claims that changes in environmental conditions can increase the numbers of some species, lead to new species over time and drive other species to extinction. Students judge cause and effect in data on fishing, fertilizers, deforestation, drought and floods. It is usually taught in Biology.
Evaluate the evidence supporting claims that changes in environmental conditions may result in: (1) increases in the number of individuals of some species, (2) the emergence of new species over time, and (3) the extinction of other species.
Clarification Statement: Emphasis is on determining cause and effect relationships for how changes to the environment such as deforestation, fishing, application of fertilizers, drought, flood, and the rate of change of the environment affect distribution or disappearance of traits in species.
Next Generation Science Standards · Disciplinary Core Idea: Biological Evolution: Unity and Diversity · Official standard
Students evaluate evidence for claims that a change in the environment caused one of three outcomes: (1) an increase in the number of individuals of some species, (2) the emergence of a new species over time, or (3) the extinction of other species. For each claim they ask the questions scientists ask: Did the cause come before the effect? Is there a comparison place or time without the change? Is there a mechanism that links the two? Are there other explanations? Is the sample large enough and repeated? They also weigh the rate of change: a species with short generations can adapt to a slow change, while a fast change can outrun adaptation and push a population to extinction.
The NGSS Clarification Statement says: "Emphasis is on determining cause and effect relationships for how changes to the environment such as deforestation, fishing, application of fertilizers, drought, flood, and the rate of change of the environment affect distribution or disappearance of traits in species." NGSS lists no Assessment Boundary for HS-LS4-5, so this lesson keeps the focus that statement sets. The cases are patterned on published studies (the collapse of northern cod, farm runoff in lakes, fish in Lake Victoria, snapping shrimp split by the Isthmus of Panama, apple maggot flies), but every data set on the page is invented for teaching and labeled that way. Students do the practice of evaluating evidence: they calculate, compare with a control, rate the strength of evidence and write a verdict with reasons.
Learning Objectives
By the end of this lesson, students will be able to:
Evaluate evidence for a claim that an environmental change increased the number of individuals of some species
Evaluate evidence for a claim that an environmental change led to the emergence of a new species over time
Evaluate evidence for a claim that an environmental change drove a species to extinction, and tell extinction apart from a local disappearance
Use timing, comparison groups, mechanisms and alternative explanations to judge whether data show cause and effect
Explain how the rate of environmental change, compared with generation time, affects whether a population adapts or disappears
Prior Knowledge Required
Students should already be comfortable with:
How natural selection leads to adaptation of populations HS-LS4-4
How changes to physical or biological parts of an ecosystem affect populations MS-LS2-4
What a species is: a group whose members can interbreed and produce fertile offspring
Calculating ratios, percent change and averages from a data table
Show a photo of a lake covered in a bright green algal bloom and read an invented headline: "Farm runoff turned the lake green."
Warm-Up Prompt
"What would you need to see before you believed this headline? List at least three kinds of evidence, and one other thing that could have caused the bloom."
Collect the lists and group them on the board under five questions: timing, comparison, mechanism, other explanations and amount of data. These become the evidence checklist for the whole lesson.
Direct Instruction15-20 minutes
Three outcomes of environmental change. When conditions change, species with traits suited to the new conditions can increase in number; populations that become separated or face different conditions can, over many generations, become new species that no longer interbreed; and species that cannot move, adapt or cope fast enough can go extinct. The rate of change matters: the number of generations a population gets to adapt equals the time the change takes divided by the generation time. Evaluating evidence means asking whether the data show that the change caused the outcome. Work through the examples below with the class checklist.
Increase: fertilizer runoff and cyanobacteria
Claim: runoff from new farms caused a rise in cyanobacteria in a lake. Invented data: over 10 years, total phosphorus rose from 0.02 to 0.08 mg/L and cyanobacteria rose from 2,000 to 90,000 cells/mL. In a similar lake with a forested watershed, phosphorus stayed at 0.02 mg/L and cells stayed near 3,000 cells/mL.
Result: Cyanobacteria rose by a factor of 90,000 / 2,000 = 45 where phosphorus rose 4 times, while the comparison lake did not change. Timing, a comparison lake and a known mechanism (phosphorus limits algal growth) make this strong evidence. The next test: check whether blooms are largest in the years with the most runoff.
Increase: fishing removes a predator
Claim: overfishing of cod caused northern shrimp to increase. Invented survey indices in Diagram 2: cod fell from 100 in 1980 to 5 in 1995; shrimp rose from 10 in 1980 to 60 in 2000.
Result: Shrimp rose by a factor of 60 / 10 = 6 after cod fell by 95%. Cod eat shrimp, and the rise came after the fall, so the claim is supported. But the ocean was also unusually cold in the early 1990s, which favors shrimp, so the evidence is moderate until the two causes are separated.
Distribution of traits: fishing and age at maturity
Claim: heavy fishing changed when cod mature. Invented data: mean age at which female cod mature fell from 6.2 years in the 1970s to 5.1 years in the early 1990s. Nets remove large, old fish first.
Result: Change: 5.1 - 6.2 = -1.1 years. Fish that mature early breed before they are caught, so alleles for early maturity are favored. An alternative is that fish grew faster when there were fewer of them; studies that compare fish of the same size and growth rate are needed to separate the two.
New species: a land bridge splits an ocean
Claim: the rise of the Isthmus of Panama about 3 million years ago split snapping shrimp populations into separate species. Invented mating trials: pairs from the same ocean paired up in 38 of 40 trials; pairs made of one shrimp from the Pacific and one from the Caribbean paired up in 4 of 40.
Result: Same ocean: 38/40 = 0.95. Across the isthmus: 4/40 = 0.10. Populations separated by the new land barrier rarely mate, which is reproductive isolation. DNA differences between each pair are consistent with a split about when the isthmus closed, so the evidence for a new species emerging after an environmental change is strong.
Extinction: murky water and lost species
Claim: water made murky by farm runoff and soil erosion caused cichlid fish species in Lake Victoria to disappear. Invented data: water clarity fell from 5 m to 1 m. At one rocky site, the number of cichlid species found fell from 24 to 9. In lab trials, females chose males of their own species in 95 of 100 trials in clear light and in 52 of 100 in murky light.
Result: Species lost at the site: 24 - 9 = 15. Females pick mates by male color, and in murky light choice drops to about chance (0.52), so species can hybridize and merge. The mechanism is supported, but an introduced predator, the Nile perch, spread at the same time. A strong verdict names both causes.
After each example, rate the evidence as strong, moderate or weak and give the reason. Then show Diagram 1: a model population whose best trait value moves each generation. Ask why a fast change leads to extinction even though the population keeps adapting.
Guided Practice15 minutes
Pairs evaluate the claim "Clearing forest increases edge-loving birds and removes forest-interior birds." The invented data come from bird surveys at five sites in one region with different amounts of remaining forest.
Guided practice data (invented): bird surveys at five sites
Site
Forest cover (%)
Forest-interior species found
Edge-species birds counted per km
1
90
14
22
2
70
11
35
3
50
8
51
4
30
4
68
5
10
1
80
Describe the pattern. (As forest cover falls, interior species fall from 14 to 1 and edge birds rise from 22 to 80 per km.)
Which outcome of the standard does each column show? (Edge birds: an increase in some species. Interior species: local losses, which could lead to extinction only if the species disappear everywhere.)
These data compare places, not one place over time. Name one other difference between the sites that could explain the pattern, and one data set that would test cause and effect.
Write a verdict: strong, moderate or weak evidence for the claim, with two reasons.
Independent Practice10-15 minutes
Each student evaluates a new invented data set. A dam built on a desert river stopped the spring floods that used to scour bare, wet sandbars. Cottonwood seeds sprout on such sandbars in spring; tamarisk (salt cedar), an introduced shrub, releases seeds all summer and sprouts on any damp ground.
Independent practice data (invented): seedlings per 100 m² of riverbank
Species
Average before the dam
Average after the dam
Cottonwood
42
3
Tamarisk
5
38
Students calculate how many times larger or smaller each count became (cottonwood about 14 times smaller, tamarisk 7.6 times larger), decide which outcome each species shows, and write a verdict on the claim that the loss of flooding caused the change. They name one comparison that would strengthen the evidence, such as a nearby river that still floods.
Closure5 minutes
Exit ticket: "A student claims that because one fish species was overfished in a river, every other fish species in the river will increase. Evaluate the claim in three sentences." Look for: only species released from predation or competition by the fished species are likely to increase; species that depended on it may decline; the claim needs counts over time and a comparison river. Return to the warm-up checklist and ask which question was hardest to answer with real data.
Differentiation Strategies
For Struggling Students
Give an evidence checklist with five yes-or-no questions (timing, comparison, mechanism, other explanations, repeated data) and have students tick it before writing a verdict
Start each case with the claim printed at the top of the card and the one number that matters most highlighted
Pair the three outcomes with a picture cue: a rising arrow for increase, a branching line for a new species, a line that stops for extinction
For Advanced Students
Ask students to rerun the Activity 3 simulation in a spreadsheet and find the fastest rate of change the population survives for 20 generations
Have students write the one experiment that would best separate the fishing and the cold-water explanations for the shrimp increase in Diagram 2
Ask students to argue why declaring a species extinct needs more evidence than declaring an increase, and what that evidence would be
Assessment Guidance
What to Look For
Strong evaluations name what would make the evidence convincing, not only what the data show: a comparison site, the right timing, a mechanism, a check on other explanations and enough data. Watch for students who accept a correlation as proof, who treat a local disappearance as extinction, or who expect a new species to appear within a few years. Check that students name which of the three outcomes a claim is about and tie it to a specific change in the environment.
02
Classroom Activities
3 Activities
1
Claim Court: Rating Evidence Cards
25 minGroups of 3-4
Each group gets three claims, one for each outcome in the standard, and three evidence cards per claim. Groups rate each card as strong, moderate or weak support, then deliver a verdict on the claim to the class "court" with the best card and the biggest gap in the evidence.
Claims and Evidence Cards (invented data)
Claim A (increase): Clearing forest for farms and roads increased white-tailed deer. A1: deer per km² in the cleared area rose from 4 to 11 over 15 years. A2: in uncleared forest 20 km away, deer rose from 4 to 5. A3: the county cut the number of hunting permits in half in year 8.
Claim B (new species): Apple maggot flies are splitting into a new species since apple trees were planted in North America. B1: flies that grow up in apples emerge about 3 weeks earlier in summer than flies that grow up in hawthorn fruit, matching the earlier ripening of apples. B2: the flies mate on the kind of fruit they grew up in. B3: in each generation, about 6 in 100 flies on each host come from the other host.
Claim C (extinction): Groundwater pumping for farms drove a desert spring snail extinct. C1: flow from its only known spring fell from 12 L/s in 1975 to 0 in 1990. C2: the snail was last seen in 1988; yearly searches from 1989 to 2010 at the spring and three nearby springs found none. C3: the snail lives only in flowing spring water.
Procedure
Rate each card and write one sentence of reasoning using the class checklist.
Decide whether each claim is supported, partly supported or not supported.
For each claim, write the one new piece of evidence that would change your verdict most.
Discussion Questions
Card A3 names another possible cause. How does card A2 help you decide how much of the deer increase to blame on clearing?
Claim B says the flies are "splitting," not "have split." Which card shows that the split is not complete, and why is that still evidence for the emergence of a new species over time?
Why are 22 years of empty searches at several springs needed before calling the snail extinct, instead of one empty search?
Modification for Distance Learning
Post each claim and its cards on a shared slide deck. Students record ratings in a form, and the class compares the results in a live discussion.
2
Flood Test: Which Seeds Win When the Soil Floods?
20 min setup, 5 min per day for 7 daysGroups of 3-4
Groups test the claim that flooding increases the number of flood-tolerant plants in a mixed seed bank. They plant rice and radish seeds together in cups that stay flooded or drained, count seedlings after 7 days and evaluate the claim with their data.
Procedure
Fill 4 clear cups with 5 cm of potting soil. In each cup, plant 20 untreated rice seeds and 20 radish seeds just under the surface.
Two cups are "flooded": keep water 3 cm above the soil. Two are "drained": poke holes in the bottom and keep the soil damp.
Count sprouted seedlings of each species on day 7 and combine the two cups of each treatment.
Safety: use untreated seeds (seed coated with fungicide is often dyed a bright color), wear gloves or wash hands after handling soil, wipe up spills and never eat seeds.
Sample Data (invented, one cup of each)
Flooded cup: 17 of 20 rice and 3 of 20 radish seeds sprouted. Drained cup: 18 of 20 rice and 19 of 20 radish sprouted. Rice made up 17/20 = 0.85 of the seedlings in the flooded cup and 18/37, about 0.49, in the drained cup.
Discussion Questions
Does flooding make rice germinate better, or does it mainly stop radish? Which numbers show this?
How is this experiment like and unlike a real wetland that starts flooding more often after a levee breaks?
What would you add to the design to make the evidence stronger?
Challenge Variation
Groups add a third treatment, cups flooded for 3 days and then drained, to test whether the length of a flood changes which species increase.
3
Can the Population Keep Up? A Rate-of-Change Simulation
25 minPairs
Pairs run a paper or spreadsheet simulation of a population whose best trait value (the "optimum," for example the best heat tolerance for the current climate) moves each generation. The population's mean trait can move at most 1 unit per generation, because selection can only work with the variation it has. Pairs compare slow and fast change and relate the results to extinction.
Rules
Start: population 500, mean trait 20, optimum 20.
Each generation: add the rate of change to the optimum, then move the mean toward the optimum by up to 1 unit. The gap is optimum minus mean.
If the gap is 1 or less, the population grows by 10% (rounded down, with a limit of 1,000). If the gap is more than 1 and up to 3, it shrinks by 10%. If the gap is more than 3, it shrinks by half. Always round down to whole individuals.
Run 12 generations with a rate of 0.5 (slow) and 2.0 (fast), and graph both.
Sample Run (slow change)
The mean keeps up every generation, so the gap stays 0. The population goes 500, 550, 605, 665, 731, 804, 884, 972 and then stays at the 1,000 limit.
Discussion Questions
With fast change, the population shrinks to 0 by generation 12. Which rule causes the collapse: the change itself or the limit on how fast the mean can move?
Try a rate of 1.5. The population also collapses, reaching 6 by generation 12, although the rate is only 0.5 more than the population can follow each generation. Why does a small excess add up?
Name two things real populations have that this model leaves out, and say whether each would make extinction more or less likely.
Modification for Distance Learning
Share a spreadsheet with the rules built in. Students change only the rate of change, screenshot their graphs and post a short claim about the fastest rate the population survives.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: Slow and Fast Environmental Change in a Model Population
Output of the Activity 3 simulation (a model, not field data). The optimum trait value rises 0.5 units per generation (blue) or 2.0 units per generation (dashed red), and the population's mean trait can move at most 1 unit per generation. Under slow change the population keeps up and grows to the 1,000 limit; under fast change the gap between the mean and the optimum widens every generation and the population reaches 0 in generation 12.
Diagram 2: Cod and Shrimp Survey Indices
Invented survey indices patterned on the collapse of northern cod off eastern Canada. The cod index (navy) falls from 100 to 5 between 1980 and 1995, and the shrimp index (dashed blue) rises afterward. The timing fits the claim that removing a predator let its prey increase; other causes, such as colder water, still need to be ruled out.
04
Homework Assignment
~30 min
HS-LS4-5 Homework: Evaluating Evidence for Environmental Change
Directions: Every data set is invented for practice but patterned on real cases. For each problem, show your calculations, say which outcome the claim is about (an increase, a new species or an extinction) and give a verdict of strong, moderate or weak evidence with reasons from the checklist: timing, comparison, mechanism, other explanations and amount of data.
Part 1: Claims about Increases (Problems 1-2)
Claim: a 3-year drought increased blue grama, a drought-tolerant grass, in a prairie. In 10 unwatered plots, its mean cover rose from 12% to 27%. In 5 plots watered during the drought, it went from 12% to 13%. (a) Find the change in each set of plots. (b) Evaluate the claim. (c) Cattle grazing was also reduced in the unwatered plots during the drought. How does that affect your verdict?
Claim: cutting rainforest increases a malaria mosquito. Surveys of 40 sites with more than 80% forest cover found the mosquito's larvae at 4 sites; surveys of 40 sites with less than 30% forest cover found them at 22 sites. (a) Find the proportion of sites with larvae in each group. (b) Evaluate the claim. (c) Cleared sites are also closer to roads, which leave sunny puddles. Design a comparison that would separate the two causes.
Part 2: Claims about New Species and Extinction (Problems 3-4)
Claim: moving plants to a new place can produce new species. In the early 1900s, three European goatsbeard species were introduced to the northwestern United States, where they grew side by side for the first time. By 1950, botanists found two new kinds of goatsbeard there. Each parent species has 12 chromosomes in its body cells; each new kind has 24. When a new kind is crossed with a parent species, 3 of 200 seeds grow into plants. (a) Find the success rate of the crosses. (b) Evaluate the claim that these are new species that arose after an environmental change. (c) Why does the chromosome count matter?
Claim: a drier climate drove a mountain toad to extinction. At its breeding pools, observers counted about 1,500 adults in 1987, 10 in 1988, 1 in 1989 and none in any year after. The number of dry-season days without mist rose from about 20 per year in the early 1970s to about 55 in 1987. (a) Find the percent drop from 1987 to 1988. (b) Evaluate the claim. (c) A disease caused by a fungus was spreading among frogs and toads in the region at the same time. What evidence would help decide between the two causes, or show that both acted together?
Part 3: Rate of Change and Weighing Claims (Problems 5-6)
A region warms over 40 years. A moth there has 4 generations per year, and a tortoise has a generation time of about 25 years. (a) Find how many generations each species has during the warming. (b) Evaluate the claim: "Both species have the same chance to adapt, because they face the same change." (c) Name one other trait, besides generation time, that affects whether a species adapts or goes extinct.
Twenty years after a large forest was cleared, three claims are made. (1) "Clearing increased an edge-loving bird": its count on survey routes rose from 1,200 to 3,100. (2) "Clearing drove a forest frog extinct": the frog, known only from that forest, has not been found in 12 years of surveys. (3) "Clearing has already produced a new bird species": birds in the fields sing slightly different songs from birds in the remaining forest. (a) Find the percent increase in claim 1. (b) Rank the three claims from best to least supported, and explain your ranking. (c) For claim 3, what evidence would be needed over time?
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Calculations
Changes, proportions, percents and generations computed correctly with units
Method correct with one error
Naming the Outcome
Says whether the claim is about an increase, a new species or an extinction, and names the environmental change
Outcome named but not linked to the change
Evaluating the Evidence
Verdict uses at least two checklist questions (timing, comparison, mechanism, other explanations, amount of data) with numbers
Verdict given with only general reasons
Next Evidence
Proposes a specific comparison or test that would separate causes
Proposes more data without saying what it would show
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Every data set is invented for practice and patterned on real cases. 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
A town claims that a new sewage treatment plant made a river's fish more abundant. Which added evidence would most strengthen the claim?
Answer: C
Choice C gives the right timing plus a comparison river, which rules out a region-wide cause such as a wet year. Choice A has the timing but no comparison. Choices B and D are anecdotes, not measurements.
Question 2 of 20 · Multiple Choice
After sea otters were hunted out of a coastal area, the density of sea urchins, which otters eat, rose from 4 to 36 per square meter. By what factor did urchin density change?
Answer: B
36 / 4 = 9, so there were 9 times as many urchins, an increase in one species after its predator was removed. Choice A is the difference, 36 - 4. Choice C is the increase divided by the start, (36 - 4)/4 = 8, which is the percent increase (800%) written as a number. Choice D divides the wrong way.
Question 3 of 20 · Multiple Choice
Which observation is the strongest evidence that two populations have become separate species?
Answer: A
Species are separated by reproductive isolation. Choices B, C and D describe differences that can exist within one species; they do not show that the populations can no longer interbreed.
Question 4 of 20 · Multiple Choice
A fast environmental change hits four species. Which species is at the greatest risk of extinction?
Answer: D
Long generations and little variation limit how fast selection can work, and a small range and low numbers leave no escape or buffer. Choices A, B and C have short generations, large populations or the ability to move, so they can adapt or relocate.
Question 5 of 20 · Multiple Choice
A lake warms over 30 years. A small minnow species in the lake has a generation time of about 2 years. How many generations does it have to adapt?
Answer: A
Generations = time / generation time = 30 / 2 = 15. Choice B multiplies instead of divides. Choice C subtracts. Choice D divides the generation time by the time.
Question 6 of 20 · Multiple Choice
A long drought hits a grassland. Which prediction about the number of individuals of each plant species is best supported by natural selection and ecology?
Answer: C
Traits that save or reach water give an advantage in drought, so those species can increase, one of the three outcomes in the standard. Choice A ignores differences among species. Choice B reverses the advantage. Choice D ignores that plants die or fail to reproduce during a drought.
Question 7 of 20 · Multiple Choice
A student claims that fertilizer runoff caused a jump in duckweed on a pond, based on one year of counts before and one year after runoff began. What is the biggest weakness of the evidence?
Answer: D
With only two years of data, a normal good year could explain the jump. More years, or a comparison pond, would show whether the change stands out. Choices A, B and C are true statements that are not weaknesses.
Question 8 of 20 · Multiple Choice
In Diagram 1, in which generation does the fast-change population first fall below half of its starting size?
Answer: B
The starting size is 500, so half is 250. The fast run goes 500, 550, 495, 445, 222, so it first drops below 250 in generation 4. Choice A is when it first falls below its starting size. Choice C is the last generation before the drop, when 445 is still above 250. Choice D is when it reaches 0.
Question 9 of 20 · Multiple Choice
How can a new geographic barrier, such as a river changing course, lead to the emergence of new species?
Answer: A
Separation lets each population's allele frequencies drift and respond to its own conditions; over many generations, reproductive isolation can build up. Choice B wrongly says individuals change their DNA. Choices C and D are not what barriers do.
Question 10 of 20 · Multiple Choice
Population X of a plant faces 2 °C of warming spread over 200 years. Population Y of the same species faces the same warming in 20 years. Which is more likely to go extinct, and why?
Answer: C
The faster change gives Y one tenth as many generations to shift its traits, so the gap between what the environment favors and what the population has can grow, as in Diagram 1. Choice B ignores the rate. Choice A reverses the reasoning, and choice D is false.
Question 11 of 20 · Multiple Choice
Duckweed cover on a pond rose from 5% to 80% after a farm upstream began using fertilizer. Which additional evidence best supports fertilizer as the cause?
Answer: D
A controlled experiment shows the mechanism: added nutrients alone speed duckweed growth. Choices A, B and C are facts that do not test the cause.
Question 12 of 20 · Multiple Choice
A frog species declined from 2,400 adults to 180 adults after its wetland was drained. What was the percent decline?
Answer: A
Decline = (2,400 - 180) / 2,400 = 2,220 / 2,400 = 0.925, or 92.5%. Choice B is the share that remains. Choice C divides 2,400 by 180. Choice D divides the loss by the final count.
Question 13 of 20 · Multiple Choice
During a long civil war, poachers killed many elephants for ivory. Afterward, a much larger share of females in one park were born without tusks. Which explanation fits best?
Answer: B
This is a change in the distribution of a trait caused by a human change to the environment: poaching selected against tusks. Choices A and D describe changes in individuals, and choice C wrongly says the environment causes the needed mutation.
Question 14 of 20 · Multiple Choice
Rising sea level split one island into two about 9,000 years ago. In invented mating trials, lizard pairs from the same island mated in 45 of 50 trials, and pairs with one lizard from each island mated in 30 of 50. Which conclusion is best supported?
Answer: D
Within an island 45/50 = 0.90, across islands 30/50 = 0.60. The drop is evidence that isolation is starting after the environmental change, but lizards that still mate in 60% of trials are not fully isolated (so not A). Choice B ignores the drop, and choice C wrongly says the environment causes the mutations.
Question 15 of 20 · Short Answer
After a forest was cut into small patches, counts of an edge-loving songbird on survey routes rose from 14 to 49 birds per route. On routes in uncut forest, counts stayed between 12 and 15. By what factor did the count rise on the cut routes, and how strong is the evidence that cutting caused the increase?
Factor: 49 / 14 = 3.5. The evidence is fairly strong: the rise came after cutting, and the uncut routes, which act as a comparison, did not change. To make it stronger, show the rise on several cut areas and explain the mechanism, for example more open nesting sites at forest edges.
Question 16 of 20 · Short Answer
Two populations of a wildflower grow next to each other, one on a rare serpentine soil and one on normal soil. The serpentine plants flower 3 weeks later, and bees rarely carry pollen between them. When botanists hand-pollinate across the two in a greenhouse, the seeds are fertile. Evaluate the claim that they are already separate species.
The claim is not yet supported. The hand crosses produce fertile seed, so the populations can still interbreed. But the flowering-time difference reduces gene flow in nature, which is evidence that a new species may be emerging over time. More generations of isolation, and evidence that hybrids do poorly, would be needed to call them separate species.
Question 17 of 20 · Short Answer
A drought cuts the flow of a river, and a population of 5,000 freshwater mussels declines by 30% each year. How many mussels are left after 3 years, and what does that suggest about extinction risk?
5,000 x 0.703 = 1,715 mussels. The population loses about two thirds of its size in 3 years. Mussels have long lives and slow reproduction, so they cannot adapt quickly; if the drought continues at this rate, the local population faces disappearance, and if this river holds most of the species, extinction.
Question 18 of 20 · Short Answer
A classmate says: "Diagram 1 proves that any species facing fast environmental change will go extinct." Evaluate this claim.
The claim overreaches. Diagram 1 is a model with made-up rules: a fixed limit of 1 unit of change per generation, no migration, no new mutations and simple growth rules. It shows that if change outpaces adaptation, a population can collapse. Real species may survive by moving, by having more variation than the model allows or by having short generations. The model supports "fast change raises extinction risk," not "always causes extinction."
Question 19 of 20 · Short Answer
A survey finds no trace of a snail species in one lake where it used to live. A student says the species is extinct. Evaluate the claim and say what evidence would be needed.
Not finding the snail in one lake shows at most a local disappearance, not extinction. Extinction means no individuals remain anywhere. The evidence needed: repeated searches over several years, at the right season and with suitable methods, across all places where the species has lived or could live, including nearby lakes, and checks of museum records to learn its full range.
Question 20 of 20 · Short Answer
A levee break turns a large area of farmland into a permanent wetland. Describe how this one environmental change could lead to each of the three outcomes in HS-LS4-5 for different species, and what evidence would support each.
(1) Increase: flood-tolerant plants and wetland birds increase; evidence: counts before and after, compared with farmland that stayed dry. (2) New species over time: if the wetland isolates a population, for example of a small fish or insect, from its relatives for many generations, it could evolve reproductive isolation; evidence over time: reduced interbreeding and DNA divergence. (3) Extinction: a species found only in that dry farmland habitat, such as a rare ground-nesting insect, could be lost; evidence: repeated surveys that find none anywhere in its range.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-LS4-5 mean?
HS-LS4-5 asks students to evaluate the evidence for claims that environmental change can increase the numbers of some species, lead to new species over time and drive other species to extinction. The emphasis is on judging cause and effect in data, not on memorizing examples. The code means High School, Life Science, core idea 4 (Biological Evolution: Unity and Diversity), performance expectation 5.
Is HS-LS4-5 taught in Biology or Environmental Science?
It is usually taught in the evolution or ecology unit of high school Biology, and it also fits Environmental Science. It follows HS-LS4-4 on adaptation, because students need natural selection to explain why some species increase and others disappear.
What does "evaluate the evidence" mean in HS-LS4-5?
It means judging how well data support a claim, not only restating the data. Students check timing (did the change come first?), comparisons (did places without the change stay the same?), a mechanism, other explanations and the amount of data, then give a reasoned verdict such as strong, moderate or weak.
Can environmental change really create new species?
Yes, over many generations. Worked example 4 on this page shows the kind of evidence needed: a barrier that formed at a known time, and populations on either side that now rarely mate. The snapping shrimp split by the Isthmus of Panama are a well-studied case.
How fast can a new species form?
It varies widely: usually thousands of generations or more, although some plants have formed new species much faster. For most animals, a few years of change can shift traits but is far too short to show a new species.
Why does the rate of environmental change matter for extinction?
Selection needs generations to shift a population, so what matters is how fast the environment changes compared with how fast a population can adapt, move or cope. A slow change may be tracked, while a fast change can leave a population poorly suited to its surroundings until it declines. Diagram 1 shows this with a simple model.
What environmental changes does the Clarification Statement mention?
It names deforestation, fishing, application of fertilizers, drought, flood and the rate of change of the environment, and it asks how these affect the distribution or disappearance of traits in species. This page uses each of them in at least one data set.
Does HS-LS4-5 have an assessment boundary?
No, NGSS lists no Assessment Boundary for HS-LS4-5. The Clarification Statement sets the emphasis on cause and effect relationships between environmental changes and the traits and survival of species.
What mistakes do students often make with HS-LS4-5?
Students often treat a correlation as proof of cause and forget to ask what happened in places without the change. Some also describe individuals adapting on purpose, or treat every species in an ecosystem as responding the same way. Asking "compared with what?" and "over how many generations?" helps correct these.
How does HS-LS4-5 connect to other standards?
It builds on MS-LS2-4 (how ecosystem changes affect populations) and HS-LS4-4 (how natural selection leads to adaptation). It runs alongside HS-LS2-6 on ecosystem stability, and it leads to HS-LS4-6 and HS-LS2-7, where students design and test solutions that reduce human impacts on biodiversity.
07
Related Standards
5 standards
These standards connect to HS-LS4-5: 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 ecosystem components affect populations
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