Energy flow in ecosystems — Geography, 14–17 years
How sunlight, plants and animals are linked, and why a change in one part of an ecosystem can affect many others.
The big idea
An ecosystem is a living community and the physical place around it. Plants capture energy from sunlight, animals get energy by feeding, and decomposers return materials to the soil. Energy moves one way through food chains, while matter such as water and carbon is recycled.
Why this matters
This idea solves a practical problem: predicting what may happen when people remove a species, add pollution or change a habitat. A food web shows that species are connected rather than living in separate boxes. It grew from attempts to explain why ecosystems can change suddenly after one apparently small disturbance.
A pond food web
Imagine a pond with 1,000 units of plant energy. If about 10% passes to insects, they hold 100 units. Small fish receive roughly 10% of that, or 10 units, and herons receive about 1 unit. If insect numbers fall sharply after pesticide use, fish have less food and herons may also decline.
The tempting mistake
A common mistake is to draw a food chain as if each species eats only one other species. That feels reasonable because a simple arrow is easy to follow, but real animals usually have several foods and predators. Use a food web when you are explaining how a change can spread through an ecosystem.
Where it is used
Conservation teams use food webs when restoring wetlands, controlling invasive species or deciding which animals can be reintroduced. Farmers also consider them when reducing pesticides, because killing one insect may affect birds, fish or pollinators. The model helps organise evidence, but it cannot predict every detail without local observations.
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