How does a food web change when one population increases or decreases? In Primary 6 Science, the answer is not found by memorising ‘predators up, prey down’. A food web contains several feeding relationships, alternative food sources and competing consumers. Students must follow the arrows, identify direct effects first and then decide which indirect effects are supported by the web and the conditions in the question.
Food-web questions are often difficult because a plausible story can outrun the evidence. If one prey population decreases, a predator may have less food, but the predator may also feed on other organisms. If one predator decreases, a prey population may face less predation, but food availability, competition and environmental conditions may also affect what happens next.
At eduKate Sengkang, Primary 6 Science tuition teaches food webs as systems. Students read arrow direction, trace one change at a time, distinguish direct from indirect effects, compare alternative pathways and write cautious conclusions that match the represented relationships rather than inventing an ecosystem story.
Use the Primary 6 Science Learning Hub, the Food Chains and Food Webs guide, and the Interactions Within the Environment guide.
- Up to three students per class.
- 1.5-hour weekly lesson.
- Focus: arrow direction, producers, consumers, population change, competition, evidence and PSLE explanations.
- Location: 83 Punggol Central, Singapore 828761.
- Enquiries: WhatsApp +65 8823 1234.
Arrow direction
The central relationship is that In a food chain or web, the arrow points from the organism being eaten towards the organism that feeds on it, representing the direction of energy transfer. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that Students who read the arrow as ‘eats’ in the opposite direction can reverse an entire population-change explanation. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Producers
The central relationship is that Green plants are producers because they make food using photosynthesis and form the base of many food relationships. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that A producer decrease can affect several consumers, but the size and certainty of the effect depend on alternative food sources and conditions. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Primary consumers
The central relationship is that Herbivores or other organisms feeding directly on producers can be strongly affected by changes in plant abundance. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that Do not assume every organism at the same trophic level has identical food sources. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Predators
The central relationship is that Predators obtain food by feeding on other organisms. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that A decrease in prey can reduce food availability for a predator, but the effect may be moderated if alternative prey remains available. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Prey
The central relationship is that Prey populations can be affected by predation pressure as well as food, habitat, disease and competition. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that A predator decrease does not prove prey will increase indefinitely. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Alternative food sources
The central relationship is that Many consumers feed on more than one organism in a food web. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that This makes food webs different from a single simple chain and is one reason one population change can have several possible outcomes. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Competition
The central relationship is that Organisms can compete when they depend on the same limited resource. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that A decrease in one competitor can increase resource availability for another, but the conclusion needs evidence that the shared resource is actually limiting. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Direct effects
The central relationship is that A direct effect follows an explicit feeding or competition relationship shown in the web. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that Students should establish direct effects before adding longer chains of indirect consequences. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Indirect effects
The central relationship is that An indirect effect occurs through one or more intermediate population changes. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that Each link adds uncertainty, so the explanation should follow the represented relationships step by step rather than jump to the final organism. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Population increase
The central relationship is that An increase means there are more individuals in the population over the stated context. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that It does not automatically mean every organism in the food web benefits or that the increase will continue forever. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Population decrease
The central relationship is that A decrease means fewer individuals are present relative to the comparison point. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that Students should identify whether the question states a cause or merely shows a change before explaining why it happened. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Food availability
The central relationship is that Population changes can alter how much food is available to consumers. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that ‘More food’ is relevant only when the organism actually eats the population that changed and no stronger limiting condition is stated. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Predation pressure
The central relationship is that More predators can increase the number of prey being eaten under suitable conditions. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that The relationship is not a deterministic guarantee because prey reproduction, migration and alternative predators can also matter. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Resource limitation
The central relationship is that Food, water, space, light and shelter can limit population growth. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that Food-web arrows show feeding relationships but do not display every environmental resource, so students must not infer absent resources without evidence. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Environmental change
The central relationship is that Pollution, drought, habitat loss or another disturbance can affect several populations at once. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that A food-web explanation should not pretend every observed change is caused only by feeding when the question states a broader environmental cause. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Migration
The central relationship is that Organisms entering or leaving an area can change population counts independently of births and deaths. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that If a question provides migration information, include it; if it does not, do not invent migration to rescue a prediction. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Reproduction
The central relationship is that Population size can change when reproduction and survival change. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that A food web alone does not directly show reproductive rate, so conclusions about births need supporting information. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Decomposers
The central relationship is that Decomposers break down dead organisms and wastes, returning materials to the environment. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that They are part of ecosystem processes but should not be inserted into every population-change answer unless relevant to the question. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Energy pathways
The central relationship is that Energy captured by producers moves through feeding relationships to consumers. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that Arrows represent transfer of energy through feeding, not a guarantee that all energy reaches the next organism. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Evidence boundaries
The central relationship is that A diagram is a simplified model of selected relationships. A strong Primary 6 answer should make that relationship visible rather than rely on general ecosystem vocabulary.
The important boundary is that The absence of an arrow may mean no feeding relationship is represented in the model; it does not prove the organisms can never interact in every real ecosystem. This matters because food-web questions reward disciplined inference: use what the model and question show, and avoid adding unsupported ecology.
In a 3-pax tutorial, each learner traces one route independently before discussion. The tutor can see whether a wrong answer began with arrow direction, alternative food sources, competition or an overextended indirect effect.
Worked Food-Web Population Cases
Predator decreases
A food web shows hawks feeding on mice, while mice also eat seeds. The hawk population decreases and no other conditions are changed in the simplified question.
Mice may experience less predation, so their population may increase if other resources remain sufficient. The answer should not claim an unlimited increase.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
One prey decreases but predator has alternatives
A snake feeds on mice and frogs. Mouse numbers fall while frog numbers remain abundant.
The snake has less of one food source, but the web does not justify saying the snake must immediately decrease because an alternative prey remains.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Producer decreases
Grass is eaten by rabbits and grasshoppers. A drought greatly reduces grass.
Both consumers can face reduced food availability. The eventual population effects may also involve competition between them for the remaining grass.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Competitor decreases
Two herbivores share the same plant resource. One herbivore population declines while plant abundance remains stable.
The remaining herbivore may experience less competition for that food. A predicted increase should still be conditional on other limiting factors.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Predator increases
Fox numbers increase in a simplified web where rabbits are a major prey.
Greater predation can contribute to a rabbit decrease under the stated conditions. The answer should identify the direct feeding relationship.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Prey increases
An insect population increases and is eaten by two bird species.
Food availability for both bird populations can increase, but the question may need additional information before predicting the size or timing of their population response.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Removing one species
A species is removed from a web containing several pathways.
Students trace every direct consumer and food source of the removed organism before predicting indirect changes. One missing species can affect several routes.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Alternative pathway protects a predator
A predator loses one prey but still has two other abundant prey species.
The food web suggests the predator may be buffered from the loss. A categorical population crash is unsupported.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Competition plus predation
Two small animals eat the same seeds, but one is also preyed on by a hawk.
A hawk decline can increase one competitor, which may then reduce seed availability for the other. The explanation needs both the direct predation change and the indirect competition link.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Pollution affects a producer
Pollution reduces an aquatic plant that supports several herbivores.
The initial effect is not predation; it is loss of a producer resource. Consumers and their predators may then be affected through the food web.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Habitat loss
A habitat change reduces nesting space for one bird species but leaves food-web arrows unchanged.
The bird population may decrease because of habitat limitation. Students should not force a feeding explanation when the question gives another cause.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Food web and migration
A prey population decreases because many individuals leave the area.
Predator food availability may fall, but the prey decrease was caused by migration in the question, not necessarily by increased predation.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Two predators share prey
Owls and snakes both eat mice. Snake numbers decrease.
Mice may face less predation from snakes, which can affect their abundance and potentially food availability for owls. The indirect owl effect needs careful reasoning.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Producer increases after rain
Rainfall increases plant growth in a simplified grassland web.
Herbivores may have more food available, but population changes depend on time and other limiting factors. The immediate plant increase does not make every consumer increase instantly.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Data contradicts a simple prediction
A food web suggests less predation should help rabbits, but measured rabbit numbers still fall.
Students should not force the expected story. Another stated factor or missing variable may be affecting the population; the data has priority over the prediction.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Food chain versus food web
In a simple chain, a predator may depend on one prey in the model. In a web, the same predator has three prey.
Students compare how alternative food sources make population predictions less direct in the web.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Arrow reversal trap
A student reads grass → rabbit → fox as ‘grass eats rabbit’.
The correction is that arrows show energy transfer through feeding: rabbit eats grass, fox eats rabbit.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Multiple-step cascade
A predator decreases, one herbivore increases, and a shared plant resource declines.
The learner states each link separately and avoids skipping from predator to plant without naming the intermediate herbivore change.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Decomposer overreach
An organism dies and a student inserts decomposers into a question asking only about a predator-prey change.
Decomposers are important, but they should be included only when relevant to the asked relationship or stated model.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
Uncertain outcome
Two competing effects act on the same population: more food becomes available but predation also increases.
The correct answer may be that the direction cannot be determined from the given information. Recognising insufficient evidence is a valid scientific conclusion.
A useful follow-up asks which effect is direct, which is indirect and which assumption the conclusion depends on. Students learn to write one link at a time and stop when the evidence no longer determines the direction.
A Food-Web Reading Routine
First identify producers and consumers. Second read every relevant arrow in the correct direction. Third mark the population that changes. Fourth list the organisms directly connected to it by feeding or clearly stated competition.
Only after direct effects are established should the learner trace indirect consequences through one additional organism. This prevents dramatic ecosystem stories that skip the mechanism.
For each predicted population change, ask what resource or pressure changed: food availability, predation, competition or another stated environmental condition. The explanation should name that mechanism.
Using Tables and Graphs With Food Webs
Population data can confirm, contradict or complicate a prediction from the diagram. Students read axes, units and time points before explaining the trend.
A food web gives possible feeding relationships; a graph gives measured population changes. The strongest answer uses both without treating either as complete on its own.
If data does not match a simple prediction, students should inspect other stated conditions rather than rewriting the data to fit the expected food-web story.
Why 3-Pax Tutorials Help
Three learners can each trace a different route from the same population change. Comparing the routes reveals whether one student ignored an alternative food source or reversed an arrow.
Students can challenge claims by asking ‘which arrow supports that?’ and ‘what intermediate population must change first?’ This keeps explanations anchored to the model.
Independent follow-up questions test whether the child can apply the same method to a new web without relying on the group’s conclusion.
Common Food-Web Errors
- Reading arrows in the wrong direction.
- Assuming a predator has only one prey when the web shows alternatives.
- Assuming a prey population always rises when one predator decreases.
- Ignoring competition for shared food.
- Skipping intermediate steps in an indirect effect.
- Treating a food web as a complete picture of every ecological interaction.
- Ignoring stated habitat, pollution or migration causes.
- Claiming population changes happen instantly.
- Using ‘more food’ without identifying which organism eats which.
- Forcing a definite answer when two opposing effects make the outcome uncertain.
Direct Versus Indirect Effects
A direct effect follows one explicit relationship; an indirect effect passes through another population. Students label the path so the explanation remains traceable.
The extension should stay inside the relationships and evidence supplied. If the direction of change cannot be determined because multiple unmeasured factors compete, saying so is stronger Science than inventing certainty.
Time Lag
Population responses may not occur immediately because reproduction, survival and movement take time. A question with time-series data should be read carefully before assuming simultaneous changes.
The extension should stay inside the relationships and evidence supplied. If the direction of change cannot be determined because multiple unmeasured factors compete, saying so is stronger Science than inventing certainty.
Competition Networks
Food webs can imply competition when two consumers share a limited resource. Students should identify the shared resource explicitly instead of merely saying the animals compete.
The extension should stay inside the relationships and evidence supplied. If the direction of change cannot be determined because multiple unmeasured factors compete, saying so is stronger Science than inventing certainty.
Producer Bottlenecks
When a major producer declines, several herbivores can be affected simultaneously. The resulting changes can then reach higher consumers through multiple paths.
The extension should stay inside the relationships and evidence supplied. If the direction of change cannot be determined because multiple unmeasured factors compete, saying so is stronger Science than inventing certainty.
Alternative Prey
Alternative prey can buffer a predator from one prey decline. This is one reason food-web reasoning is more complex than a single chain.
The extension should stay inside the relationships and evidence supplied. If the direction of change cannot be determined because multiple unmeasured factors compete, saying so is stronger Science than inventing certainty.
Habitat and Food Together
A population can be affected by both feeding relationships and habitat availability. The answer should prioritise the cause stated in the question rather than assume feeding always dominates.
The extension should stay inside the relationships and evidence supplied. If the direction of change cannot be determined because multiple unmeasured factors compete, saying so is stronger Science than inventing certainty.
Human Impact
Pollution, hunting, land-use change or conservation actions can alter populations directly. The food web helps trace later effects, but does not erase the initial human cause.
The extension should stay inside the relationships and evidence supplied. If the direction of change cannot be determined because multiple unmeasured factors compete, saying so is stronger Science than inventing certainty.
Evidence From Repeated Surveys
Population counts can vary naturally and measurements can be imperfect. Repeated surveys provide stronger evidence than one isolated count, especially when making claims about trends.
The extension should stay inside the relationships and evidence supplied. If the direction of change cannot be determined because multiple unmeasured factors compete, saying so is stronger Science than inventing certainty.
Model Limits
A classroom food web selects a small number of organisms and relationships. Strong students learn to use it faithfully without pretending it is a complete ecosystem map.
The extension should stay inside the relationships and evidence supplied. If the direction of change cannot be determined because multiple unmeasured factors compete, saying so is stronger Science than inventing certainty.
PSLE Answer Compression
A long ecosystem paragraph is not automatically better. A strong answer identifies the changed population, the affected feeding or competition relationship and the resulting change, then stops when the requested link is complete.
The extension should stay inside the relationships and evidence supplied. If the direction of change cannot be determined because multiple unmeasured factors compete, saying so is stronger Science than inventing certainty.
Counterfactual Reasoning
Ask what would happen if the original population had not changed. This helps students isolate the role of the change and distinguish it from background conditions.
The extension should stay inside the relationships and evidence supplied. If the direction of change cannot be determined because multiple unmeasured factors compete, saying so is stronger Science than inventing certainty.
Checking Direction Twice
Students can verbalise each arrow as ‘is eaten by’ before writing. This small routine prevents reversed chains that would otherwise corrupt several marks at once.
The extension should stay inside the relationships and evidence supplied. If the direction of change cannot be determined because multiple unmeasured factors compete, saying so is stronger Science than inventing certainty.
What Progress Looks Like
The learner reads arrows correctly, marks direct connections first and uses alternative food sources when they are shown.
Open-ended answers become stepwise: changed population → changed food or predation pressure → effect on another population. Indirect effects are written only after the intermediate link is established.
Students also become more comfortable recognising uncertainty. They stop treating every food web as a deterministic machine with one guaranteed outcome.
Frequently Asked Questions
What do arrows in a food web mean?
They show the direction of energy transfer through feeding, from the organism being eaten towards the consumer.
If predators decrease, will prey always increase?
Not necessarily. Food, competition, habitat and other predators can also affect prey populations.
If one prey decreases, must the predator decrease?
Not if alternative food sources remain sufficient. Read the entire food web.
What is a direct effect?
A change transmitted through an explicit feeding or competition relationship without another population in between.
What is an indirect effect?
A consequence that occurs through one or more intermediate population changes.
Can food-web questions have uncertain answers?
Yes. If opposing effects or missing information prevent a justified direction, the correct conclusion may be that more evidence is needed.
Why are food webs harder than food chains?
They include multiple feeding pathways and alternative food sources, so one population change can have several connected effects.
Does this replace the whole Environment topic?
No. It is a focused population-change owner. Use the Primary 6 Science Learning Hub for adaptations, human impact, resources and wider interactions.
Primary 6 Food-Web Checklist
- Have I read every relevant arrow in the correct direction?
- Which population changed first?
- Which organisms are directly connected to it?
- Did food availability, predation or competition change?
- Are there alternative food sources?
- Am I skipping an intermediate population?
- Does the question state another cause such as habitat loss or migration?
- Is the final direction actually determined by the evidence?
Continue through the Primary 6 Science Learning Hub.
eduKate Sengkang teaches Primary Science in focused groups of up to three students. Lessons are by appointment. For current class availability, WhatsApp +65 8823 1234.
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