Food Chains and Energy Transfer
Follow the sun's energy up a food chain and see how little of it reaches the top. Sunlight falls on grass, and the plants capture only a small share. Each time something is eaten, only a fraction of its energy ends up in the animal that ate it. The rest is lost as heat from living and moving, as waste, or in parts that are not eaten. A bar for each level, drawn to the same scale, shows the energy there, and a second bar beside it shows what was lost on the way up. Set how much sunlight falls, how much the plants capture, how much is passed up each step, and how many levels the chain has (3 to 5). For instance, with the starting settings 4,000,000 kJ of sunlight per square metre a year becomes 40,000 kJ in the grass but only 40 kJ in the top animal.
Preview — sign up free to change the numbers yourself
What you can adjust
- Sunlight energy
- 1000000 – 8000000 kJ/m²/yr
- Share captured by plants
- 1 – 3 %
- Energy passed up each step
- 5 – 20 %
- Number of feeding levels
- 3 – 5
The sunlight energy falling on each square metre of ground in a year. 4,000,000 kJ is about 1,100 kWh, a sunny place with a mild climate. More sunlight means more energy at every level, in the same proportions.
How much of the sunlight the plants turn into food by photosynthesis. Most of it is reflected, passes through the leaves or is the wrong colour, so even a healthy field captures only 1 to 3 percent.
The share of a level's energy that ends up in the animals that eat it. The rest is lost as heat from living and moving, as waste, or in parts that are not eaten. About 10 percent is typical.
How many levels the food chain has, counting the plants as the first. Every extra level multiplies the energy at the top by the share passed up, so long chains are rare.
About this simulation
What it shows
Sunlight falls on grass, and the energy climbs a food chain one level at a time. A bar for each level shows how much energy it holds, and a second bar beside it shows how much was lost on the way up, as heat, waste and parts that were not eaten.
The key idea
Only a small part of the energy passes from one level to the next, so each level holds far less than the one below. That is why food chains are short and top predators are few.
Try this
Run the defaults: 40,000 kJ in the grass falls to 40 kJ at the top. Set Energy passed up each step to 20% and the top gets 320 kJ. Set Number of feeding levels to 5 and it drops to 4 kJ.
All the bars use one scale, the grass bar being full width, so the upper bars are very thin and the smallest are drawn at a minimum width so you can still see them. The losses are split 60% heat, 25% waste and 15% uneaten parts at every step; the numbers are typical averages, not measurements of one place. The picture is played in 9 seconds. On narrow screens the loss bars sit under the energy bars, and the sunlight that was not captured is shown as a table row.