Life is always dependent directly or indirectly on the energy from the sun.
In every ecosystem, there is an organism at the lowest level that converts energy from the sun into
usable energy for other organisms.
All organisms in an ecosystem can be placed in trophic levels depending on what energy source they rely upon and how they provide energy for other organisms in the food web.
With the exception of life near hydrothermal vents in the deep ocean, life is always dependent directly or indirectly on the energy from the sun. In every ecosystem, there is an organism at the lowest level that converts energy from the sun into usable energy for other organisms.
The structure and dynamics of a community depend to a large extent on the feeding relationships between organisms – the trophic structure of the community. The transfer of food energy up the trophic levels from its source in plants and other photosynthetic organisms (primary producers) through herbivores (primary consumers) to carnivores (secondary and tertiary consumers) and eventually to decomposers is referred to as a food chain.
Each step in a food chain is called trophic level. Trophic level is the feeding position in a food chain such as primary producers, primary consumers,secondary consumers ,decomposers etc .The producers or green plants form the first trophic level. Herbivores form the second trophic level, while carnivores form the third and even the fourth trophic levels.