Question

How are animals classified according to their role in the food chain

Answer 1

Animals are usually placed as primary consumers that is herbivores (plant eaters) and Secondary consumers that is carnivores (meat eaters) and omnivores (both plant and animal eaters). While, the Producers or the autotrophs are generally the green plants are capable of synthesising the organic matter (glucose) from the inorganic substances such as CO2 and water with the help of sunlight so they occupy the first trophic level.  

Answer 2

the animals are classified according to their trophic levels that is the first trophic levels are the producers which produce the energy, the second level contains the primary consumers or the herbivores, the third contains secondary consumers and so on. all the animals present above the second level are Carnivores or omnivores the last level is called the top level. each level is consumed by the level just above it. however a level may or may not consume any level below it other than the level just below it.

the producers absorb the energy of the Sun to produce food.
the second trophic level that is the primary consumers consume these producers. then the primary consumers are themselves consumed by the secondary consumers which are again consumed by the tertiary consumers.this goes on till top consumers. generally there are 4 trophic levels in a food pyramid.