Ecosystems, Energy Flow & Recycling

An ecosystem is all the living organisms (the community) and the non-living (abiotic) factors in an area, interacting together.

Energy flow

Energy enters via producers (photosynthesis) and flows through trophic levels: producer → primary consumer → secondary consumer → tertiary consumer. Energy is lost at each transfer (typically only ~10% passes on) through respiration (heat), excretion and parts not eaten. This is why food chains rarely exceed 4–5 levels and why pyramids of energy always narrow upwards.

Gross primary productivity (GPP) = total energy fixed by producers.
Net primary productivity (NPP) = GPP − respiratory losses = energy available to the next level.