MS-LS2-2: Predicting Patterns of Interactions Among Organisms in Ecosystems
In plain English: MS-LS2-2 is the NGSS middle school performance expectation that asks students to construct an explanation that predicts how organisms interact in different ecosystems. Competition, predation and mutually beneficial partnerships follow the same patterns in a desert, a coral reef or a forest, even though the species differ. It is usually taught in middle school life science.
Construct an explanation that predicts patterns of interactions among organisms across multiple ecosystems.
Clarification Statement: Emphasis is on predicting consistent patterns of interactions in different ecosystems in terms of the relationships among and between organisms and abiotic components of ecosystems. Examples of types of interactions could include competitive, predatory, and mutually beneficial.
Next Generation Science Standards · Disciplinary Core Idea: Ecosystems: Interactions, Energy, and Dynamics · Official standard
Students build explanations that predict how organisms will interact, and they test those predictions in several ecosystems. An ecosystem is all the living things in an area together with the nonliving parts they depend on, such as water, sunlight, soil and temperature. Students meet three kinds of interactions: competition, when two organisms need the same limited resource; predation, when one organism (the predator) eats another (the prey); and mutualism, a mutually beneficial partnership in which both organisms gain. The big idea is that these patterns repeat. A cactus and a bat in a desert, a cleaner fish on a coral reef and a fungus on a tree root are different species, but the patterns of their interactions are the same, so students can use what happens in one ecosystem to predict what will happen in another.
The NGSS Clarification Statement says: "Emphasis is on predicting consistent patterns of interactions in different ecosystems in terms of the relationships among and between organisms and abiotic components of ecosystems. Examples of types of interactions could include competitive, predatory, and mutually beneficial." This performance expectation has no Assessment Boundary. Abiotic means nonliving, so students also look at how a nonliving factor, such as how much water there is, changes an interaction. All data sets on this page are invented for teaching and labeled as invented; the facts about real species (for example, that yucca moths pollinate yuccas) are real.
Learning Objectives
By the end of this lesson, students will be able to:
Identify competition, predation and mutualism from descriptions and from data on how each organism does with and without the other
Describe the predator-prey pattern in population data, in which the predator population rises and falls after the prey population
Explain how a nonliving factor, such as a shortage of water, can make an interaction stronger or weaker
Construct an explanation, with a claim, evidence and reasoning, that predicts how two organisms will interact in an ecosystem they have not studied
Prior Knowledge Required
Students should already be comfortable with:
How matter moves among plants, animals, decomposers and the environment 5-LS2-1
How some organisms survive well, less well or not at all in a habitat 3-LS4-3
Show three photos without labels: two kinds of seabirds diving for the same school of fish, a hawk carrying a snake, and a bee on a flower. Ask students what each pair of organisms is doing to the other.
Warm-Up Prompt
"For each photo, decide whether each organism is helped, harmed or not affected by the other. Then think of a pair of organisms from a completely different place, such as an ocean, a desert or your backyard, that you think interact in the same way."
Collect a few pairs on the board under "both harmed", "one helped, one harmed" and "both helped". Tell students that these three columns are the three patterns of interactions for today, and that the goal is to predict which column a new pair belongs in, and what will happen to each population.
Direct Instruction15-20 minutes
Three patterns that repeat. A population is all the members of one species living in an area. A resource is something an organism needs, such as food, water, light or space. When a resource is limited, there is not enough of it for every organism that needs it. Use a sign table to name an interaction: write + if an organism does better because the other is there, and - if it does worse.
Competition (-, -): both organisms need the same limited resource, so each does worse when the other is present. Competition can be between members of the same species or of different species.
Predation (+, -): the predator gains food and the prey is eaten. Prey numbers often rise first, then predator numbers rise, then prey numbers fall, then predator numbers fall: the predator follows the prey.
Mutualism (+, +): both partners gain. Some partners depend on each other so much that neither can reproduce without the other.
An explanation that predicts has three parts: a claim (what will happen), evidence (data or observations) and reasoning (the pattern that links the evidence to the claim). Work through the examples, using Diagram 1 with the second and Diagram 2 with the fourth.
Competition in a garden (sign table - , -)
Invented data from a school garden. Lettuce in weeded rows: mean head mass 400 g. Lettuce in rows where crabgrass was left to grow: 240 g. Crabgrass growing alone in a bare row: 800 g per meter of row; crabgrass growing among the lettuce: 560 g per meter.
Result: Lettuce: (400 - 240) ÷ 400 = 0.40, a 40% drop. Crabgrass: (800 - 560) ÷ 800 = 0.30, a 30% drop. Both do worse together, so the sign table is (-, -): competition for light, water and soil nutrients. Prediction: two kinds of coral growing side by side on a reef also compete, for space and light, so each will grow less than it would alone.
Predation: the predator follows the prey (Diagram 1)
Invented counts in a rose garden. Aphids (tiny insects that suck plant juice) on 10 marked stems, weeks 0 to 10: 40, 90, 180, 260, 210, 120, 60, 40, 50, 90, 150. Ladybugs (which eat aphids) on the whole row: 2, 3, 5, 10, 16, 18, 12, 7, 4, 3, 4.
Result: Aphids peak at 260 in week 3; ladybugs peak at 18 in week 5, two weeks later. As aphids become scarce, ladybugs fall to 3 by week 9, and the aphids rise again. Prediction: in a northern forest, the number of weasels that eat voles (small rodents) will rise and fall a little after the number of voles does.
Mutualism: partners that depend on each other
Real relationship, invented counts. In deserts of the southwestern United States, a female yucca moth carries pollen from one yucca flower to another and lays her eggs inside the flower. Her caterpillars eat some of the developing seeds. A class reads that on one plant, 40 flowers were covered with fine mesh that kept moths out and 40 were left open: 0 covered flowers and 26 open flowers made seed pods.
Result: Open flowers: 26 ÷ 40 = 65% made pods; covered flowers: 0%. The yucca needs the moth to make seeds, and the moth's caterpillars need yucca seeds to eat, so the sign table is (+, +). The caterpillars eat only some seeds, so the plant still gains. Prediction: in a place where yucca moths disappeared, yuccas would make almost no seeds, and fewer young yuccas would grow over the years.
A nonliving factor changes the interaction (Diagram 2)
Invented data from a meadow study, mean of 6 plots per group. Grass B growing alone: 200 g per plot in watered plots and 120 g in dry plots. Grass B growing with grass A, whose roots take water from the same soil: 180 g in watered plots and 60 g in dry plots.
Result: Watered: 180 ÷ 200 = 90% of its mass alone. Dry: 60 ÷ 120 = 50%. Competition costs grass B much more when water, a nonliving resource, is scarce. Prediction: in a drought year, two kinds of shrubs whose roots share the same desert soil will compete more strongly than in a rainy year.
Using a sign table to classify and predict
Real relationship, invented counts. In Central America, ants live inside the hollow thorns of bullhorn acacia trees and feed on sugary liquid and food the tree makes. A study (invented numbers) compares trees with ants and trees whose ants were removed: leaves damaged by plant-eating insects 8% against 45%; height growth in a year 64 cm against 16 cm. Ant colonies that were moved off their trees, away from food and shelter, did not survive.
Result: Trees do better with ants: growth is 64 ÷ 16 = 4 times as much (+). Ants do better with trees (+). Sign table (+, +): mutualism. Prediction: if a disease killed the acacias in one valley, the acacia ant population there would fall too, and any surviving acacias without ants would lose more leaves to insects.
After each example, ask: "What would the data have to look like for this to be a different interaction?" For example, if the lettuce grew better with crabgrass, the sign table would no longer be (-, -). This question trains students to tie each prediction to evidence.
Guided Practice10-15 minutes
Pairs analyze invented data from four ecosystems. Each row shows how each organism does when the other is present and when it is not.
Guided practice data: four pairs in four ecosystems (invented)
Ecosystem and pair
Organism 1: without partner
Organism 1: with partner
Organism 2: without partner
Organism 2: with partner
Pond: two kinds of snails grazing algae on the same rocks
60 eggs per week
35 eggs per week
50 eggs per week
30 eggs per week
Grassland: clover and bumblebees
3 seeds per flower head (bees kept out by mesh)
54 seeds per flower head
15 g nectar stored per nest per week (no clover nearby)
40 g nectar stored per nest per week
Tide pool: periwinkle snails and green crabs
140 snails per m² (crabs caged out)
50 snails per m²
1 g gained per crab in a month (no snails to eat)
6 g gained per crab in a month
Forest: oak and maple seedlings in the same shady gap
30 cm growth in a year
18 cm growth in a year
40 cm growth in a year
31 cm growth in a year
For each row, write + or - for each organism, then name the interaction (competition, predation or mutualism).
For the pond snails and the forest seedlings, find the percent drop for each organism when the partner is present. What do the two rows have in common, even though one is underwater and one is on land?
State the pattern as a rule that would work in any ecosystem, for example: "When two organisms need the same limited resource, ..."
Predict: in a desert, two kinds of shrubs take water from the same patch of soil. Use your rule to predict how each shrub will grow with and without the other, and name the evidence from this table that supports your prediction.
Independent Practice10-15 minutes
Each student writes an explanation that predicts. On coral reefs, clownfish live among the stinging tentacles of certain sea anemones (animals related to corals). A slimy coating protects the clownfish from the stings, the tentacles protect the clownfish from predators, and the clownfish chase away fish that bite anemones.
Independent practice data: anemones and clownfish on one reef (invented)
Observation
Anemones with clownfish
Anemones without clownfish
Change in anemone size over one year
grew by 30%
shrank by 10%
Tentacles bitten off by fish in one month
2 per anemone
17 per anemone
Survey divers also found all 40 clownfish they counted within 1 m of an anemone. Students (1) fill in the sign table and name the interaction, (2) write a claim that predicts what will happen to the clownfish population on a reef where warm water kills many anemones, and (3) support it with evidence from the table and reasoning from the pattern. A strong answer predicts that clownfish numbers will fall, because the fish depend on anemones for shelter from predators, and that the surviving anemones will be bitten more.
Closure5 minutes
Exit ticket: "In a cave, bats leave droppings on the floor, and cave beetles feed on the droppings. Two kinds of beetles feed on the same droppings. Name the interaction between the two kinds of beetles, and predict what happens to each beetle population if half of the bats leave the cave." (Competition; with less food, the competition gets stronger and both beetle populations shrink.) Return to the warm-up columns and have students add one new pair to each column from an ecosystem not yet on the board.
Differentiation Strategies
For Struggling Students
Give a printed sign table with the two organisms already listed and the + and - symbols to circle
Provide an explanation frame: "I predict ___ because in the data ___. This fits the pattern of ___, in which ___."
Use only the first two rows of the guided practice table and compare raw numbers before finding percents
For Advanced Students
Ask students to find a pair whose interaction changes with conditions, such as two plants that compete when water is scarce but not when it is plentiful, and explain the change
Have students graph the Activity 3 results and compare the timing of the peaks with Diagram 1
Ask students to research one more mutualism in an ecosystem on another continent and write a prediction for what would happen if one partner disappeared
Assessment Guidance
What to Look For
Check that students name an interaction from evidence about both organisms, not just one. A (+) for one partner is not enough to call it mutualism. Look for predictions that state what will happen to each population and that give a reason based on a pattern, not just a guess. Watch for students who call any two organisms in the same place competitors, and for students who expect the predator to peak at the same time as the prey.
02
Classroom Activities
3 Activities
1
Interaction Card Sort: Same Pattern, Different Places
15 minGroups of 3-4
Groups sort 12 cards that describe pairs of organisms from four ecosystems. They first sort the cards by ecosystem, then re-sort them by type of interaction, and notice that every ecosystem has all three types.
The 12 Cards
Desert: creosote bushes and other desert shrubs take water from the same dry soil; roadrunners catch and eat lizards; lesser long-nosed bats drink nectar from saguaro cactus flowers and carry pollen from flower to flower.
Coral reef: corals grow toward each other and compete for space and light; reef sharks eat smaller fish; small cleaner wrasse fish eat parasites off the skin of larger fish, which come to them to be cleaned.
Forest: young trees in a gap in the forest grow toward the same patch of sunlight; owls hunt mice at night; fungi wrapped around tree roots pass water and minerals to the tree and take in sugar the tree makes.
Arctic tundra: red foxes and arctic foxes hunt the same small animals and use the same kinds of dens where their ranges overlap; snowy owls eat lemmings (small rodents); in a lichen, a fungus and an alga live together, the alga making food and the fungus giving shelter and holding water.
Procedure
Sort the cards into four ecosystem piles. Then shuffle them and sort them into three interaction piles: competition, predation and mutualism.
For each card, write the sign table (+ or - for each organism) on a sticky note.
Write one sentence that describes a pattern you see in the three piles, for example, how many ecosystems appear in each pile.
Predict: the teacher hands out two blank cards for a grassland. Groups invent a likely pair for two of the three interactions and justify each with the pattern.
Discussion Questions
Each of the four ecosystems has exactly one card of each interaction type. Do you think a fifth ecosystem, such as a pond, would also have all three? Why?
The bats and the cleaner wrasse are very different animals in very different places. What is the same about their interactions?
Which card was hardest to sort, and what extra information would have helped?
Modification for Distance Learning
Post the 12 cards on a shared digital board. Students drag them into columns, then post a pattern sentence and one grassland prediction.
2
Bean Competition Lab: Plenty or Scarce
20 minGroups of 3
Students model two bird species that eat the same seeds. One "species" picks up dried beans with a clothespin, the other with a plastic spoon. They feed alone and together, with plenty of beans and with few, and use the data to explain when competition is strongest.
Procedure
Spread 200 dried beans in a tray (plenty). The clothespin bird feeds alone for 30 seconds, dropping beans into a cup, while a timer counts. Count the beans, return them, then repeat with the spoon bird alone.
Both birds feed in the same tray at the same time for 30 seconds. Count each cup.
Repeat all three rounds with only 60 beans in the tray (scarce). The third student times and records.
Safety: beans stay out of mouths, noses and ears, and the group picks up spilled beans at once so nobody slips. Feed by picking up beans only, never by pushing or grabbing another student's tool.
With plenty of beans, each bird got 5 fewer beans when feeding together. With scarce beans, the clothespin bird got half as many and the spoon bird 10 fewer. When was competition stronger, and why?
Which part of the model stands for a nonliving factor in a real ecosystem, such as rainfall that makes more or fewer seeds?
Predict what would happen to the two "populations" over several seasons if the tray always held only 60 beans.
Modification for Distance Learning
Students use dried pasta or buttons at home with a family member as the second bird, or analyze the sample data and write the explanation.
3
Ladybugs and Aphids: A Tabletop Predator-Prey Model
25 minPairs
Pairs model a predator and its prey on a 30 cm × 30 cm square of desk marked with masking tape. Small paper squares (1.5 cm) are aphids and cardboard squares (8 cm) are ladybugs. Over 10 generations, pairs record both populations and look for the predator-prey pattern.
Rules for Each Generation
Start with 20 aphids scattered on the square and 1 ladybug.
Toss each ladybug card once from about 30 cm above the square. Remove every aphid the card touches: the ladybug ate them.
A ladybug that ate 3 or more aphids survives and adds 1 new ladybug. A ladybug that ate fewer than 3 starves and is removed.
The aphids that are left double, up to a limit of 120, because the plant has only so much room.
If no ladybugs are left, 1 new ladybug flies in for the next generation.
Sample Data (one invented run that follows the rules above)
Generations 1-10. Aphids at the start: 20, 32, 50, 64, 60, 40, 28, 22, 34, 62. Ladybugs at the start: 1, 2, 4, 8, 12, 12, 10, 2, 2, 1. Aphids eaten: 4, 7, 18, 34, 40, 26, 17, 5, 3, 3. Ladybugs that ate 3 or more: 1, 2, 4, 6, 6, 5, 1, 1, 0, 1.
Discussion Questions
In the sample data, aphids peak in generation 4 and ladybugs peak in generations 5 and 6. Why does the predator peak come after the prey peak?
Why do the aphids start to rise again in generations 9 and 10?
What does the limit of 120 aphids stand for in a real garden, and is it a living or nonliving part of the ecosystem?
Challenge Variation
Change one rule, such as a smaller ladybug card (a predator that hunts less well) or a limit of 60 aphids, predict how the graph will change, then run 10 generations to test the prediction.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: Aphids and Ladybugs in a Rose Garden
Invented weekly counts, drawn to scale. Top: aphids (prey) on 10 marked stems. Bottom: ladybugs (predator) on the whole row. The ladybug peak in week 5 comes two weeks after the aphid peak in week 3, and both populations fall and then begin to rise again.
Diagram 2: Competition Is Stronger When Water Is Scarce
Invented dry mass of grass B per plot, drawn to scale. In watered plots grass B still reaches 90% of its mass alone when grass A shares the soil, but in dry plots it reaches only 50%. A nonliving factor, water, changes how strongly the two grasses compete.
04
Homework Assignment
~30 min
MS-LS2-2 Homework: Predicting Interactions in Ecosystems
Directions: All data sets are invented for practice. Show each calculation. When a problem asks you to predict, write a claim, the evidence you used and the pattern that connects them.
Part 1: Naming Interactions from Data (Problems 1-3)
Tadpoles of two frog species were raised in pond-water tanks, 50 per tank. Spring peepers alone: 42 survived to become young frogs; spring peepers with gray treefrog tadpoles: 30 survived. Gray treefrogs alone: 40 survived; with spring peepers: 31 survived. (a) Find the percent that survived in each of the four tanks. (b) Make a sign table and name the interaction. (c) Predict how two kinds of seed-eating birds on a small island would do in a dry year with few seeds, and explain.
Spider mites are tiny pests that suck juice from strawberry leaves, and predatory mites eat them. Mites per leaf on a strawberry farm, weeks 1 to 8: spider mites 6, 15, 32, 48, 30, 14, 8, 10; predatory mites 1, 2, 4, 8, 13, 11, 5, 3. (a) In which week does each population peak, and how many weeks apart are the peaks? (b) Explain the pattern. (c) Predict what would happen to the spider mites if the farmer sprayed something that killed only the predatory mites.
Bees visit cherry trees for nectar and pollen and carry pollen between flowers. On one tree, 150 flowers were covered with mesh bags that kept insects out and 150 were left open. Bagged flowers made 6 cherries; open flowers made 48. (a) Find the percent of flowers that made cherries in each group. (b) What does each partner gain? Name the interaction. (c) Predict what would happen to cherry harvests in an orchard where bee colonies died out, and explain.
Part 2: Predicting Across Ecosystems (Problems 4-6)
Three studies kept predators out of small fenced or netted areas and counted the prey inside and outside. Meadow, birds kept out with netting: grasshoppers per m² 8 outside and 20 inside. Rocky shore, birds that eat limpets (small shelled animals) kept out with cages: limpets per m² 15 outside and 75 inside. Pond, fish kept out with mesh: dragonfly young per sample 6 outside and 18 inside. (a) For each study, how many times as many prey were inside? (b) State the pattern that all three ecosystems share. (c) Predict what would happen to beetles on a forest floor if the salamanders that eat them were kept out of some plots.
A student claims: "Mutualism only happens in warm tropical places." Evidence from two studies: in a cold mountain meadow, flowers bagged to keep bumblebees out made seeds in 5% of flowers, while open flowers made seeds in 55%; in an oak woodland, jays bury acorns to eat in winter, and in one clearing 70% of the young oak trees grew from acorns the jays buried and never dug up. (a) What does each partner gain in each study? (b) Do these studies support or weaken the claim? Explain.
Two lizard species on an island eat the same kinds of insects. Insects caught per trap: 60 in a normal year and 25 in a drought year. Mean mass gain per lizard of species A over the summer: alone on a nearby islet, 12 g in a normal year and 7 g in a drought year; on the shared island, 10 g in a normal year and 3 g in a drought year. (a) For each kind of year, find the percent of its alone mass gain that species A reached on the shared island. (b) Explain how the drought changed the interaction. (c) Construct an explanation that predicts what will happen to both lizard populations if droughts become more frequent.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Calculations
Percents, times-as-many comparisons and peak timing are correct
Correct method with one calculation error
Naming the Interaction
Sign table uses evidence about both organisms and names the correct interaction
Correct interaction, but evidence about only one organism
Prediction
Claim, evidence and reasoning are all present, and the reasoning names a pattern that applies to the new ecosystem
Claim and evidence present, but the reasoning does not connect them to a pattern
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
In a mountain meadow, two kinds of hummingbirds drink nectar from the same flowers, and each kind chases the other away from flower patches. Which interaction is this?
Answer: B
Both birds need the same limited resource and each does worse when the other is there, which is the (-, -) pattern of competition. Choice A confuses taking food with eating the other organism; in predation one organism eats the other. Choice C is wrong because mutualism means each partner helps the other, and here they chase each other off. Choice D ignores that they harm each other without eating each other.
Question 2 of 20 · Multiple Choice
Invented data from a lake: arms of the lake where pike (a large fish) were present had 12 minnows per net, and arms netted off from pike had 45. Pike kept with minnows gained weight, and pike kept without minnows lost weight. Which interaction do the data show?
Answer: C
Pike do better with minnows (+) and minnows do worse with pike (-): the (+, -) pattern of predation, with pike as the predator. Choice A ignores that pike gain weight when minnows are present. Choice D looks only at the minnows; naming an interaction needs evidence about both organisms. Choice B reverses the minnow data.
Question 3 of 20 · Multiple Choice
On sandy sea floors, some shrimp dig burrows that a small fish called a goby shares. The goby, which sees well, flicks its tail to warn the nearly blind shrimp of danger. Invented data: shrimp with a goby partner spent 5 times as long outside the burrow feeding, and gobies with a burrow to hide in survived longer. Which sign table fits?
Answer: A
The shrimp gains warnings and more feeding time, and the goby gains a place to hide, so both partners gain: mutualism. Choice D ignores the evidence that the shrimp feeds longer with a goby. Choice B would need one partner to be eaten or harmed, and choice C would need both to do worse together.
Question 4 of 20 · Multiple Choice
On a prairie, foxes hunt rabbits. Rabbit numbers peaked in year 3 of a survey. Based on the predator-prey pattern, when are fox numbers most likely to peak?
Answer: C
Predators raise more young when prey are plentiful, so the predator population grows after the prey population and peaks a little later. Choice B misses that it takes time for more foxes to be born and grow up. Choice A has the order backwards. Choice D ignores that the foxes' food supply changes.
Question 5 of 20 · Multiple Choice
Invented garden data: in weeded rows, 80 onions per row grew to full size; in rows where weeds were left, 52 did. By what percent did weeds lower the number of full-size onions?
Answer: B
The drop is 80 - 52 = 28 onions, and 28 ÷ 80 = 0.35, a 35% drop. Choice A reports the drop in onions (28) as if it were a percent. Choice C divides by the new value: 28 ÷ 52 ≈ 0.54. Choice D is the share that still grew, 52 ÷ 80 = 0.65, not the drop.
Question 6 of 20 · Multiple Choice
Two kinds of seaweed grow on the same rocks in a tide pool, and each needs open rock to attach to. In which situation would you predict the competition between them to be strongest?
Answer: D
Competition is strongest when the shared resource is scarce. On crowded rocks there is little open space, a nonliving resource both kinds need, so each seaweed does worse when the other is there. Choices A and B describe plenty of open rock, where each kind can find room. Choice C removes one competitor, so there is no competition between the two kinds at all.
Question 7 of 20 · Multiple Choice
Invented data for moss A on stream rocks. In wet shade: 40 mm of growth alone, 34 mm with moss B. In dry sun: 20 mm alone, 9 mm with moss B. Which statement do the data support?
Answer: B
Wet shade: 34 ÷ 40 = 0.85, or 85%. Dry sun: 9 ÷ 20 = 0.45, or 45%. Competition costs moss A more where water is scarce. Choice C compares amounts: the drops are 6 mm and 11 mm, which are not equal. Choice D treats the growth in millimeters as percents. Choice A is wrong because moss A grows less, not more, with moss B.
Question 8 of 20 · Multiple Choice
A student writes: "Hawks and mice compete with each other because they live in the same field." Which response is best?
Answer: C
Living in the same place does not make two organisms competitors. Hawks eat mice, so the hawk gains and the mouse loses: predation. Choice A is the error in the student's claim: competition needs a shared limited resource. Choice B names something they have in common, not a limited resource they share. Choice D has no evidence behind it: the mouse is harmed.
Question 9 of 20 · Multiple Choice
Tiny mites ride on the backs of burying beetles to reach dead animals, where the beetles raise their young. To show that this is mutualism and not just the mites getting a free ride, which extra evidence is needed?
Answer: A
We already know the mites gain a ride. Mutualism needs evidence that the beetles gain too, such as more young. (In nature, these mites eat fly eggs that would compete with the beetle young for food.) Choice B shows only the mites' benefit, which is the free-ride idea. Choices C and D show that the two are found together, not that both gain.
Question 10 of 20 · Multiple Choice
A kind of orchid in a forest is pollinated by only one kind of bee: that is, only this bee carries its pollen from flower to flower so seeds can form. Predict what happens if the bee disappears from the forest.
Answer: D
When a plant depends on one partner for pollination, losing the partner means few or no seeds, so fewer new orchids grow and the population shrinks over time. Choice B ignores the stem: only this bee carries the pollen. Choice C assumes a fast change that the evidence does not support. Choice A ignores that the orchid needs the bee to make seeds.
Question 11 of 20 · Multiple Choice
Invented data from a field: plots with spiders had 14 leafhoppers (small plant-eating insects) per net sweep, and plots where spiders were kept out had 49. How many times as many leafhoppers were in the plots without spiders?
Answer: A
49 ÷ 14 = 3.5, so there were 3.5 times as many leafhoppers without the predators. Choice C is the difference, 49 - 14 = 35, not a times-as-many comparison. Choice B divides the wrong way: 14 ÷ 49 ≈ 0.29. Choice D adds the counts: 49 + 14 = 63.
Question 12 of 20 · Multiple Choice
Invented weekly counts in a pond, weeks 1 to 8. Water fleas (prey): 20, 60, 140, 90, 40, 30, 50, 100. Backswimmers, insects that eat water fleas: 3, 4, 8, 15, 12, 6, 4, 5. How many weeks after the prey peak does the predator peak?
Answer: D
Water fleas peak at 140 in week 3, and backswimmers peak at 15 in week 4: 1 week later. Choice A assumes the peaks happen together. Choice B counts from week 2, where the prey were still rising. Choice C counts from the prey peak to week 6, when the backswimmers had already fallen.
Question 13 of 20 · Multiple Choice
Clover and bumblebees are a mutualism: the bees carry clover pollen and get nectar. Which pair from another ecosystem shows the same pattern?
Answer: A
The bird gains food and the tree gains seeds carried to new places where they can grow, so both gain (+, +), like the bees and clover. Choice B is competition for space. Choice C is predation. Choice D is competition for light.
Question 14 of 20 · Multiple Choice
A student studied a coral reef and a desert. Which prediction about the two ecosystems is best supported by the patterns of interactions?
Answer: D
Competition, predation and mutualism are patterns found across ecosystems, even though the species that take part are different. Choice C confuses the patterns with the species. Choices A and B claim an interaction is missing from one ecosystem, but sharks eating fish and bats pollinating cactus show predation on reefs and mutualism in deserts.
Question 15 of 20 · Short Answer
Invented data: 100 beetle larvae (young beetles) of species A were raised in each of two containers of flour, one alone and one with species B. 60 survived alone and 36 with B. For species B, 50 of 100 survived alone and 30 with A. Find the percent of its alone survival that each species reached when they lived together, name the interaction and predict what happens if the flour is cut in half.
Species A: 36 ÷ 60 = 60%. Species B: 30 ÷ 50 = 60%. Both do worse together, so the sign table is (-, -): competition for flour. Prediction: with half the flour, the food is scarcer, so competition gets stronger and both species survive in smaller numbers.
Question 16 of 20 · Short Answer
In a lake, small fish eat zooplankton (tiny floating animals). Describe how a graph of the two populations over several years would most likely look, and predict what happens to the zooplankton if many extra small fish are added to the lake one spring.
Both lines rise and fall, and the fish line rises and falls a little after the zooplankton line, because the fish population grows when food is plentiful and shrinks when food runs short. After the extra fish are added, the zooplankton are eaten faster, so the zooplankton fall; then the fish run short of food and also fall, and the zooplankton can rise again.
Question 17 of 20 · Short Answer
Ants guard young treehoppers (small sap-sucking insects) on plants and drink the sugary liquid the treehoppers give off. Invented data: on plants with ants, 38 of 50 young treehoppers survived; on plants where ants were kept away, 12 of 50 survived. Find both survival percents, name the interaction and predict what happens to the treehoppers if the ants are removed from a whole field.
With ants: 38 ÷ 50 = 76%. Without ants: 12 ÷ 50 = 24%. The treehoppers gain protection and the ants gain food, so the sign table is (+, +): mutualism. Prediction: without ants, more young treehoppers are eaten by predators, so the treehopper population in the field shrinks.
Question 18 of 20 · Short Answer
Finch A lives alone on Island 1 and eats about 9 seeds per minute. On Island 2, finch A shares the island with finch B, which eats seeds of the same size, and finch A eats about 5 seeds per minute (invented data). Construct an explanation (claim, evidence, reasoning) that predicts what would happen to finch A on Island 1 if finch B arrived there.
Claim: if finch B arrives on Island 1, finch A will get fewer seeds and its population will likely shrink. Evidence: on Island 2, where both live, finch A eats about 5 seeds per minute instead of 9, about 4 fewer. Reasoning: both finches need the same limited seeds, which is the pattern of competition, and that pattern works the same way on any island.
Question 19 of 20 · Short Answer
Plan an investigation to test whether two kinds of pond snails compete. Describe the setups, what you would measure, what you would keep the same and what result would show competition.
Setups: tanks with snail 1 alone, snail 2 alone, and both together, with the same total number of snails, several tanks of each. Keep the same: tank size, water, light, temperature and amount of algae. Measure: eggs laid or growth per snail over a few weeks. Competition is shown if each kind does worse with the other than alone (-, -).
Question 20 of 20 · Short Answer
Herons wade in a pond and catch frogs. In a wet year, a heron caught 2 frogs per hour; in a dry year, when the pond shrank to a small pool, a heron caught 9 frogs per hour (invented data). How many times as many frogs per hour were caught in the dry year? Explain how the nonliving change affected the interaction, and predict the effect on the frog population.
9 ÷ 2 = 4.5 times as many frogs per hour. Less water is a nonliving change: the frogs are crowded into a small pool where herons find them easily, so predation gets stronger. Prediction: the frog population falls faster in the dry year, and fewer frogs are left to lay eggs next spring.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does MS-LS2-2 mean?
MS-LS2-2 asks middle school students to construct an explanation that predicts how organisms interact in different ecosystems. The code stands for Middle School, Life Science, core idea 2 (Ecosystems: Interactions, Energy, and Dynamics), performance expectation 2.
What grade is MS-LS2-2 taught in?
It is a grades 6-8 standard, and schools place it in whichever middle school year holds the ecosystems unit, often grade 6 or grade 7. It pairs well with MS-LS2-1 (resources and populations) and MS-LS2-3 (matter and energy in ecosystems).
What are the three types of interactions in MS-LS2-2?
The Clarification Statement names competitive, predatory and mutually beneficial interactions. In competition both organisms do worse because they need the same limited resource; in predation one organism eats the other; in mutualism both partners gain.
Is parasitism part of MS-LS2-2?
Not as an official example. The Clarification Statement says examples "could include" the three types above, so a teacher may add parasitism, in which one organism lives on or in another and harms it, as a fourth pattern. This page does not assess it.
What does it mean to predict a pattern across ecosystems?
It means using an interaction pattern seen in one ecosystem to say what will happen in another. If two snails that share algae in a pond both do worse together, students can predict that two shrubs sharing water in a desert will also both do worse together, because the pattern is the same even though the species differ.
How is competition different from predation?
In competition neither organism eats the other: both need the same resource, such as food, water, light or space, and both do worse. In predation the predator eats the prey, so the predator gains and the prey loses. Two animals that eat the same food compete; an animal that eats the other is a predator.
Why does the predator population peak after the prey population?
Predators need time to raise more young when food is plentiful, so their numbers rise after the prey numbers rise. When there are many predators, the prey are eaten faster and fall, and then the predators run short of food and fall too.
Where do nonliving factors fit in this standard?
The Clarification Statement asks about relationships with abiotic (nonliving) components too. A nonliving factor can change how strong an interaction is: in a drought, plants that share soil compete more strongly, and deep snow that hides voles from hawks makes predation weaker.
What are common mistakes students make?
Students often call any two organisms in the same place competitors, name an interaction from evidence about only one organism, or expect the predator and prey to peak at the same time.
What comes after MS-LS2-2?
In high school, HS-LS2-6 asks students to evaluate claims that interactions keep the numbers and types of organisms relatively steady in stable conditions, and HS-LS2-1 uses math to explain what limits populations. Both build on the interaction patterns from MS-LS2-2.
07
Related Standards
6 standards
These standards connect to MS-LS2-2: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
5-LS2-1Prerequisite
Model the movement of matter among plants, animals, decomposers and the environment
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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