Grass catches sunlight and stores it as energy. A gazelle eats grass, but most of that energy gets used up just walking, breathing and staying warm — only about a tenth is left to build gazelle. A lion eating the gazelle loses nine-tenths again. So by the time you reach the top, there is hardly any energy left, which is why there are far fewer lions than gazelles. Slide the grass up and down and count for yourself.
Most people think predators are rare mainly because they are hard to hunt or breed slowly. In fact it is energy: only about a tenth passes up at each feeding level, so by the top of the chain there is barely any energy left to support more than a few.
What's actually happening
It looks like a question about hunting, but it is really a question about energy, and the answer is one of the tidiest rules in biology. Picture the chain: grass turns sunlight into food, gazelles eat the grass, lions eat the gazelles. At each step, you might expect most of the energy to carry up. It does not. The animal eating spends the vast majority of what it swallows just staying alive — moving, breathing, pumping blood, keeping warm. Only a small slice is left over to actually become more animal.
The slice is famously about a tenth. An ecologist named Raymond Lindeman pinned this down in the 1940s studying a Minnesota lake: roughly 90% of the energy at any level is burned off or lost as heat and waste, and only around 10% makes it up to the next mouth. So if grass holds a hundred thousand units of energy, gazelles get ten thousand, and lions get a thousand — a hundredth of what the grass started with. That is the energy pyramid the simulator draws: each band a tenth of the one below, narrowing fast.
This single rule shapes whole landscapes. It is why food chains almost never run more than four or five links — by then there is simply no energy left to support another level of hunter. It is why top predators are always rare and always the first to vanish when an ecosystem is squeezed. And it is the hard reason behind a familiar bit of advice: eating plants directly skips a step, so a field can feed far more people growing grain than raising the cattle that eat the grain. Nine-tenths lost at every step is a steep tax, and nothing alive gets out of paying it.
Only a tenth of energy passes up each feeding level, which is why top predators are always rare and chains stay short.
- 1Count out 1,000 dried beans into a bowl — that is your grass energy.
- 2Take out a tenth (100 beans) into a second bowl for the gazelles, then a tenth of that (10 beans) into a third bowl for the lions.
- 3Line the three bowls up. The lion bowl looks almost empty next to the grass bowl — and that gap, drawn in beans, is exactly why big predators are so rare.
Common questions
The animal doing the eating spends most of what it swallows just staying alive, moving, breathing and keeping warm, losing it as heat and waste. Only around a tenth is left over to build more animal.
Because roughly nine-tenths of the energy is lost at every step, after four or five links there is simply no energy left to support another level of hunter. The pyramid runs out of fuel.
Eating plants directly skips a step in the chain. Since about 90% of energy is lost turning feed into cattle, the same field can feed many more people growing grain than raising the cattle that eat it.