The relationships in a community within an ecosystem can be shown using food chains and food webs. Food chains are made up of stages known as trophic levels. The direction of the energy and matter flowing from one trophic level to the next is represented by arrows.
Food chains always begin with producers which are able to produce their own food. Photosynthesis is the main route by which energy enters an ecosystem. Photosynthetic bacteria, plankton, algae and plants are able to take energy and matter from the environment as opposed to other living organisms which depend on consuming other organisms.
| Trophic level | Consumer type |
| ProducerPrimary consumerSecondary consumer | Produces its own food via photosynthesisConsumer that eats plants (herbivore)Consumer that eats other animals (carnivore) |
Energy and Food production
As you can see, especially from the pyramids of energy, energy transfer from one tropic level to the next in natural ecosystems is very inefficient.
An ecosystem can be measured by its productivity. Productivity is the amount of biomass which is produced by that ecosystem on an annual basis. It’s possible to measure primary productivity, which is the amount of plant biomass the ecosystem produced, or secondary productivity, which is the amount of biomass produced by consumers.
Gross primary productivity (GPP) is the amount of energy fixed by producers during photosynthesis and then stored as chemical energy. Gross secondary productivity (GSP) is the amount of energy that absorbed by consumers. Energy is lost at trophic levels and the actual energy that can be passed on is known as the net primary productivity (NPP) (for producers) or the net secondary productivity (NSP) (for consumers).
Net productivity can be worked out by the following equation:
net productivity = gross productivity – respiratory and heat loss