The sun is the ultimate source of energy in most ecosystems and for almost all living things. Energy from the sun flows through ecosystems allowing nutrients to be produced. They are able to use the light energy from the sun to produce carbohydrates through a process called photosynthesis . There are usually several levels that energy flows through from producers to consumers. Each level is called a trophic level.
Primary producers make up the lowest trophic level.
The second level consists of those organisms which feed entirely on plants. These organisms are are known as herbivores or primary consumers . Carnivores are those organisms that feed on herbivores and other animals. They are referred to as secondary consumers and make up the third trophic level. Occasionally some carnivores eat other carnivores.