Australian Curriculum v9 / ACiQ Year 7 Science - Unit 4 - Food webs and population change

Food webs and population change

Interpret food webs and predict how changes to biotic and abiotic factors can affect populations.

Updated 2026-07-24 - 8 min read

Interpret food webs and predict how changes to biotic and abiotic factors can affect populations. This note connects the core scientific model to a worked example, an inquiry design and the limits of the evidence.

Core model

A food web represents who provides matter and energy to whom. Population prediction follows a change through arrows while considering biotic factors, abiotic factors and alternative pathways.

Accessible diagram description: Text web: sunlight supports grass; arrows run grass → grasshopper → frog → heron, grass → rabbit → fox, and grasshopper → small bird → fox. The description states that arrows point toward the consumer.

A model is useful because it highlights relationships that help explain or predict evidence. It is not a perfect copy of reality. Always state what the representation includes, what its arrows or symbols mean, and one relevant limitation.

Authored representation workshop

Connected wetland food web

Accessibility description: Arrows point from food source to consumer. Grass supplies grasshopper and rabbit; grasshopper supplies frog and small bird; frog supplies heron; rabbit and small bird supply fox.

Represented parts

  • Grass
  • Grasshopper
  • Rabbit
  • Frog
  • Small bird
  • Heron
  • Fox

Represented relationships

  • Grass -> Grasshopper (food to consumer)
  • Grass -> Rabbit (food to consumer)
  • Grasshopper -> Frog (food to consumer)
  • Grasshopper -> Small bird (food to consumer)
  • Frog -> Heron (food to consumer)
  • Rabbit -> Fox (food to consumer)
  • Small bird -> Fox (food to consumer)

Learner action: Starting at grass, trace two different pathways to a top consumer. Then predict one direct and one indirect consequence of drought, using conditional language and naming a relationship the model omits.

Monthly wetland survey

Accessibility description: Frog count generally rises as insect count rises. Survey 5 has many insects but few detected frogs during windy conditions, so detectability is a plausible limitation.

| Survey month | Insects counted | Frogs counted | Conditions | | --- | --- | --- | --- | | 1 | 18 | 3 | calm | | 2 | 25 | 5 | calm | | 3 | 34 | 7 | light breeze | | 4 | 42 | 9 | calm | | 5 | 45 | 3 | windy | | 6 | 53 | 11 | calm |

*Same approved path, survey duration, area and non-contact counting method.*

Learner action: Plan a non-contact observational survey from an approved path, using fixed time, area and counting rules. Analyse the supplied six-month table, distinguish correlation from causation, explain the windy-survey anomaly and identify further evidence needed to test the food-web prediction.

The representation and table are supplied evidence. Do not replace a represented value, relationship or anomaly with an expected result. If a visual version is created, preserve this text-equivalent information and define every symbol, arrow, heading and unit.

Worked example

The reasoning routine is:

  1. identify the observation, measurement or represented relationship
  2. select the relevant science idea
  3. connect the idea to the evidence in a complete sentence
  4. qualify the answer when the evidence or model has a boundary

Inquiry connection

Question: How did frog abundance change as wetland insect abundance changed across six monthly surveys?

Reasoned hypothesis: If insect abundance increases, frog abundance will tend to increase because more prey is available.

  • Independent variable: observed insect abundance across survey months
  • Dependent variable: frog abundance
  • Relevant controls: survey area, time, duration and counting method
  • Hazard: wetland edges can be slippery and wildlife should not be disturbed
  • Risk control: survey from approved paths with supervision and use non-contact observations
  • Reproducibility detail: state sites, dates, survey duration, weather limits and counting rules

Possible data finding: frog counts generally rose with insect counts, but one windy survey recorded few frogs despite many insects.

Evidence-based interpretation: The overall pattern supports the hypothesis; wind may have reduced frog detection in the anomalous survey.

Limitation: Correlation across six surveys does not prove insects alone caused frog changes.

This investigation frame recurs across Year 7 Science. A sound response names a testable relationship, matches the hypothesis to the same variables, manages a realistic risk, specifies quantities and measurement rules, analyses the full data pattern, supports a claim with evidence and states what the evidence cannot establish.

Common errors and corrections

  • Error: Reading arrows from predator to prey. Correction: Return to the core model and identify the exact evidence or relationship before answering.
  • Error: Treating a web as separate single chains. Correction: Return to the core model and identify the exact evidence or relationship before answering.
  • Error: Predicting a certain outcome without conditions. Correction: Return to the core model and identify the exact evidence or relationship before answering.
  • Error: Ignoring abiotic influences such as rainfall. Correction: Return to the core model and identify the exact evidence or relationship before answering.

Practice

  1. Trace two pathways from a producer to a predator.
  2. Predict one direct and one indirect effect of fewer insects.
  3. Explain how drought could enter the web.
  4. Name data needed to test the prediction.

Transfer task

Apply the topic to the investigation below without relying on a teacher or AI to mark the reasoning.

Evidence status: activity only. Use the task-specific rubric below for self-review or teacher feedback; completion does not automatically award mastery.

Context: How did frog abundance change as wetland insect abundance changed across six monthly surveys?

  1. Rewrite the question if it does not clearly name the relationship and measurable outcome.
  2. Write the matching reasoned hypothesis: include the expected direction and the science idea that justifies it.
  3. Identify the independent variable, dependent variable and at least three relevant controlled variables.
  4. Write a six-step reproducible method. Include equipment, quantities, units, an ordered measurement rule and at least three repeated trials for each condition.
  5. State the hazard, possible harm and a practical control. The control must address the stated hazard rather than being generic advice.
  6. Design a results table with headings and units. State which graph or other representation would best show the relationship and why.
  7. Use this possible finding: frog counts generally rose with insect counts, but one windy survey recorded few frogs despite many insects. Describe the overall pattern, identify any anomaly and state a reasonable check.
  8. Write a conclusion using claim, specific evidence and scientific reasoning. Finish with this limitation: Correlation across six surveys does not prove insects alone caused frog changes.

Correction guide: Compare the question and hypothesis to confirm they use the same two variables. In the method, circle every quantity and unit and underline every controlled condition. In the data response, separate the broad pattern from any anomalous result. In the conclusion, highlight the evidence sentence and box the limitation. If one of these parts is absent, revise that part before checking the scientific vocabulary.

An excellent transfer response is precise without pretending the evidence is perfect. It makes the chain from question to method to data to claim visible, and it explains how the core model applies in the unfamiliar context.

Task-specific inquiry rubric

  • Question and hypothesis for observed insect abundance across survey months and frog abundance: Names the same measurable relationship in both and gives a scientific reason. Revise if needed: Align the changed factor, measured outcome and predicted direction.
  • Fair, safe and reproducible method: Controls survey area, time, duration and counting method, manages "wetland edges can be slippery and wildlife should not be disturbed", and specifies quantities, units, measurement rules and repeats. Revise if needed: Replace vague directions and generic safety advice with operational detail.
  • Data and analysis plan: Provides labelled headings and units, an appropriate representation, a way to describe the whole pattern and a rule for checking anomalies. Revise if needed: Show how evidence will answer the question before collecting it.
  • Scientific interpretation and boundary: Links the expected evidence to food webs and population change and anticipates this boundary: Correlation across six surveys does not prove insects alone caused frog changes. Revise if needed: Explain the science link and state what the design cannot establish.

Self-check

For each response, check:

  • Did I use the correct scientific vocabulary?
  • Did I refer to the specific evidence, feature or data?
  • Did I explain the link rather than only naming it?
  • Did I avoid claiming more than the model or data support?
  • If an investigation is involved, did I address question, hypothesis, variables, safety, reproducibility, data, evidence and limitations?

Sources