This tool gives you an original pond food web with seven species: alga, pondweed, snail, tadpole, water beetle, small fish and heron. You remove one species and it explains the plausible effects on predators, prey and food chains. It also tracks energy along one chain at a percentage you choose.
The aim is to practise careful wording: what the model supports, and what it does not.
How do I use it?
- Read the web above. Each line reads “food, food → feeder”, so “alga, pondweed → snail” means the snail eats both.
- Choose one species to remove. The tool starts with the tadpole.
- Answer the arrow-meaning question: in “alga → snail”, what does the arrow show?
- Enter the energy in the producer in kJ, which starts at 10000, and the percentage passed on at each step, which starts at 10.
- Press Explore. Reset restores the starting values.
The energy must be positive, and the percentage must be above 0 and at most 100.
Example walk-through
With the tadpole removed, the tool reports two predators affected. The beetle loses one food source but still eats snails, and the fish loses one but still eats beetles, so their numbers may fall and the model does not predict extinction.
The tadpole’s own food is alga, so alga loses a predator. The tool offers three plausible effects: its numbers rise, they stay similar if other feeders remain, or they rise and then fall if its own food runs short. The model cannot say which.
The chains leading to the heron are listed, and two are struck through as broken because they pass through the tadpole. Two chains remain through the snail.
The energy table starts at 10000 kJ in the alga. At 10% it gives 1000 kJ in the snail, 100 kJ in the beetle and 10 kJ in the fish. Try 20% and the fish holds 80 kJ, but the lesson is the same: each step has less than the last.
How do I read the result?
- Removed line: the species you chose.
- Bullet list: effects on feeders that lose a food, and on the species that was eaten by the removed one. Words such as “may” and “plausible” are intended.
- Chains to the heron: a struck-through chain has lost a link, but the heron is not automatically lost.
- Energy table: energy at each level along alga, snail, beetle, fish.
- Arrow feedback: tells you whether your arrow meaning was correct.
What are the assumptions and limits?
The web and its links are an original model, and the energy values are whatever you type, not measured data. The tool makes no forecast for any real ecosystem and gives no advice about invasive species.
Treat every result as a possibility, and check your syllabus on the Cambridge subject page for the wording your course expects.
Which lessons explain the output?
Begin with constructing a food chain with the correct arrow meaning, then interpreting a food web change without claiming one inevitable outcome.
The energy table links to explaining energy losses between trophic levels. The full topic is ecology and energy flow, and the mixed practice set has more questions. For a dataset version, see interpreting a food-web or land-cover dataset. The tools page lists the other tools.
If you often answer with certainty where the evidence only allows “may”, our team can practise that wording with you. See online one-to-one Biology tuition.