Biomass decreases as you move up a food chain. At each level, roughly 90% of the energy stored in living matter is lost, leaving only about 10% available to support the next level of consumers. This is why plants vastly outweigh herbivores, herbivores outweigh predators, and top predators are the rarest organisms in any ecosystem.
The 10% Rule
The pattern behind shrinking biomass is sometimes called the “10% rule.” Trophic efficiency, the percentage of energy that actually transfers from one level to the next, typically falls between 5% and 20%, with 10% as a rough average. That means if a grassland contains 10,000 kilograms of plant biomass, only about 1,000 kilograms of herbivore biomass can be supported by it, and only about 100 kilograms of predator biomass above that.
This creates the classic pyramid shape you see in ecology textbooks: a wide base of producers tapering to a narrow point at top predators. The pattern holds whether you measure energy, biomass, or population numbers, though each type of pyramid has its quirks.
Where the Energy Goes
The 90% that “disappears” at each level doesn’t vanish. It gets used up by the organisms themselves. Consider a rabbit eating grass. Some parts of the plant, like tough stems and roots, pass through the rabbit’s body undigested and leave as waste. Of the portion the rabbit does absorb, a large fraction fuels its daily life: maintaining body temperature, building proteins, running from foxes, and simply keeping its cells alive. All of that metabolic work converts the chemical energy stored in food into heat, which radiates away and can’t be recaptured by the next consumer.
Only the small fraction of energy that gets built into the rabbit’s actual body tissue (muscle, fat, organs) becomes available to whatever eats the rabbit. This is why warm-blooded animals are especially “wasteful” from an energy standpoint. They burn a huge share of their calories just staying warm.
How This Limits Food Chain Length
Because biomass shrinks so dramatically at every step, most food chains top out at four or five levels. There simply isn’t enough energy left to sustain another tier of predators. A study published in Nature Communications found that predator biomass scales with prey biomass at roughly a three-quarter power relationship. In practical terms, a five-fold increase in prey biomass only supports about a three-fold increase in predator biomass. The higher you go, the harder it becomes to pack on additional consumer biomass.
This is why apex predators like wolves, sharks, and eagles exist in small populations spread across large territories. They sit at the top of a funnel that has filtered out most of the original energy. Removing or reducing the base of that funnel, through habitat loss or overharvesting of prey, hits top predators hardest because they have the thinnest margin to begin with.
Global Biomass by the Numbers
The scale of this pyramid is staggering when you look at the whole planet. A comprehensive census published in the Proceedings of the National Academy of Sciences estimated that plants account for roughly 450 gigatons of carbon globally. All animals on Earth, from insects to whales, total about 2 gigatons of carbon. That means producers outweigh all animal life by more than 200 to 1.
Fungi weigh in at about 12 gigatons, and bacteria at around 70 gigatons, but both of those groups largely function as decomposers rather than occupying traditional spots in the food chain. The animal figure, just 2 gigatons, captures the cumulative effect of energy loss at every trophic level across every ecosystem on the planet.
When the Pyramid Flips Upside Down
Not every ecosystem follows the classic pyramid shape for biomass. In the open ocean, consumer biomass can actually exceed producer biomass at any given moment. The global marine data bears this out: roughly 1 gigaton of carbon in marine primary producers supports about 5 gigatons of consumer biomass. That looks impossible if energy is always lost at each step, but the explanation comes down to turnover speed.
Phytoplankton, the tiny organisms that form the ocean’s producer base, reproduce incredibly fast. A population can double in a day or two. So even though the standing stock of phytoplankton at any snapshot in time is small, their total production over weeks and months is enormous. Zooplankton and fish accumulate biomass over much longer lifespans, so at any given moment they outweigh their food source. The energy flow still follows the pyramid rule. It’s only the snapshot of living weight that appears inverted.
Inverted biomass pyramids have also been documented on pristine coral reefs and in kelp forests, where large predatory fish outweigh smaller prey fish. Research in the Proceedings of the Royal Society B found that these patterns require energy subsidies from outside the immediate habitat, such as mobile fish that feed across multiple reef systems or seasonal pulses of plankton from upwelling currents. Without those external inputs, the math doesn’t work.
Human Activity and Biomass Distribution
Human impact has reshaped the natural biomass pyramid in dramatic ways. Industrial fishing and whaling have cut the biomass movement of marine animals roughly in half since 1850, disproportionately removing large-bodied consumers at the top of ocean food chains. On land, human biomass movement now exceeds the combined biomass movement of all wild birds, land arthropods, and wild land mammals by about six to one. When you factor in all forms of human transport, that ratio jumps to about 40 to one.
Because environmental disturbances tend to hit larger organisms at higher trophic levels hardest, activities like overfishing, habitat destruction, and climate change make biomass pyramids steeper and more bottom-heavy than they would naturally be. The top of the pyramid, already thin by the laws of thermodynamics, gets shaved even thinner by human pressure.