The trophic level interaction involves three concepts namely:-

1. Food Chain

2. Food Web

3. Ecological Pyramids

FOOD CHAIN:- Organisms in the ecosystem are related to each other through feeding mechanism or trophic levels, i.e. one organism becomes food for the other. A sequence of organisms that feed on one another, form a food chain. A food chain starts with producers and ends with top carnivores.

The sequence of eaten and being eaten, produces transfer of food energy and it is known as food chain.

The plant converts solar energy into chemical energy by photosynthesis. Small herbivores consume the plant matter and convert them into animal matter. These herbivores are eaten by large carnivores.

Types of Food Chains:- In nature, two main types of food chains have been distinguished:

i) Grazing food chain:- The consumers which start the food chain, utilising the plant or plant part as their food, constitute the grazing food chain. This food chain begins from green plants at the base and the primary consumer is herbivore.

For example, In terestrial ecosystem, grass is eaten up by caterpillar, which is eaten by lizard and lizard is eaten by snake. In Aquatic ecosystem phytoplanktons (primary producers) is eaten by zoo planktons which is eaten by fishes and fishes are eaten by pelicans.

ii) Detritus food chain: It starts from dead organic matter of decaying animals and plant bodies consumed by the micro-organisms and then to detritus feeding organism called detrivores or decomposer and to other predators.

The distinction between these two food chains is the source of energy for the first level consumers.

In the grazing food chain the primary source of energy is living plant biomass while in the detritus food chain the source of energy is dead organic matter or detritus. The two food chains are linked. The initial energy source for detritus food chain is the waste materials and dead organic matter from the grazing food chain.