An ecosystem is a community of organisms interacting with each other and with their environment. A community is made up of different types of populations. A population is all of the organisms of one species within a single habitat.

Photosynthesis is the main route by which energy enters an ecosystem. Energy is transferred up the trophic level in food chains and food webs. The food chain describes the relationship between producers, consumers, and decomposers. Many food chains may overlap to create a food web, which shows the interconnection and relationships between feeding networks.

At the base of the food chain are the primary producers. Primary producers are autotrophic organisms that convert solar energy into organic energy. Above the primary producers are the consumers who ingest live plants, and are the prey of other carnivores that are higher up in the food chain. Decomposers, such as bacteria, molds and fungi, obtain nutrients by secreting enzymes to break up the chemical compounds that make up dead plant and animal matter. Both consumers and decomposers are considered heterotrophic, which means they obtain energy from other organisms.

Marine trophic pyramid with 6 levels. The green arrow going from the yellow circle named ‘sun’s energy’ points towards the first and lowest level of the pyramid, presenting purple and green coral reef like structures called ‘primary producers’. Second level presents yellow shells and is called ‘herbivorous consumer’. Third level presents a crab and a prawn, and is called ‘first level carnivorous consumers’. Fourth level presents an average fish and is called ‘second level carnivorous consumers’. The fifth level presents a squid and is called ‘third level carnivorous consumers’. The sixth and top level presents a shark and is called ‘top carnivores’. Grey arrows are going from the left side of all six levels and point towards the orange shape on the top left of the image, called ‘heat energy loss’. Another set of grey arrows going from the right side of all six levels point towards the green shape with a name ‘’decomposer. From the green shape, the last arrow is pointing towards the bottom level of the pyramid.

The different trophic levels can be represented using numbers:

  • Level 1: Plants and algae, which make their own food (primary producers)

  • Level 2: Herbivores, which eat plant matter (primary consumers)

  • Level 3: Carnivores, which eat herbivores (secondary consumers)

  • Level 4: Carnivores, which eat other carnivores (tertiary consumers)

  • Level 5: Apex predators, which have no natural predators (top of the food chain)