Question

what happens if we remove predators from food web ?

Answer 1

If we remove predators from food chain there will be an increase in the population oh the prey (without any increase in the food available to the prey) due to which inter specific competition increases and the prey population decreases.
Species gets extinct. 

Answer 2

Removing any level from an ecosystem disrupts a delicate balance that may have evolved over millions of years. These systems are comprised of a series of checks and balances between predator and prey, that tend to balance the whole. The removal of the top predators in an ecosystem has several impacts, some of which are expected, and others surprising.