Energy Transferred In Ecosystems

Stand in a wheat field on a bright afternoon and an enormous amount of energy is pouring onto every square metre around you. Almost none of it ends up in the grain. Ninety nine parts in a hundred bounce off, slip past or warm the soil, and of the fraction the crop does capture, most is spent again before anything reaches a cow, a sparrow or you. Ecosystems are not efficient machines. They leak at every joint.

This lesson follows that leak from end to end. You will find out why plants and algae hold on to only about one per cent of the light that reaches them, why roughly nine tenths of the biomass at any feeding level never makes it to the level above, and where the missing nine tenths actually goes. Then you will use the numbers: tracking one animal's whole yearly ledger from mouthful to growth, building a pyramid of biomass to scale, and reading one you are handed in an exam closely enough to say what it tells you about the ecosystem and what it cannot.