Trophic levels and energy transfer, productivity, ecological succession, and the carbon and nitrogen cycles.
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.
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