Question

predict what would happen to lions if suddenly all rabbits are disappeared from forest?

Answer 1

if suddenly all the rabbits are disappeared from the forest, this will disturb the food chain as they are primary consumers and the lions would die due to food scarcity as they are secondary consumer.  
but if there are others animals also which lion can feed, then they won't die.

Answer 2

the whole ecosystem will be disturbed....even just a small mosquito plays a vital role in our environment....perhaps,without rabbits,lions would be affected badly