List the reasons why food chains do not tend to exceed four links

Due to loss of energy at each tropic levels.

Explanation:

Food chain may be defined as the sequential level of tropic levels in which the organisms eat other animals and itself being eaten by other animals. The plants acts as producers in the food chain.

The food chain is limited up to 3-4 tropic levels only. The energy is lost at each tropic level according to the 10% law of energy. The limitation of energy and its lost makes the food chain limited only up to few tropic levels. Instead of food chain, food web exist in nature.

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.