Lions and tigers are considered as apex predators in the food chain. Their size, strength, claws and canines makes them a dangerous adversary.
Naturally these animals do not have any predators. But bears, elephants and big buffaloes can be a challenge for lions and tigers and can inflict considerable damage or even death upon these big cats during a defensive outcome.
A pack of Asiatic wild dogs known as Dholes can be a potential predator of the tigers. But Dholes never prefer these animals as a choice of prey until forced to do so.
But HUMANS are the biggest predator for each and every living species on the planet.
Typically the there are 4–5 trophic levels in a food chain because only 10% of the energy available at a trophic level is transferred to the next trophic level. Hence if we start with 100% energy at trophic level 1(producers), the amount of energy successively decreases to 10%(trophic level 2) to 1%(trophic level 3) to 0.1%(trophic level 4) finally to 0.01% at trophic level 5(apex predators). Therefore, in nature very long food chains are non existent !