Technically humans are not the top of the FOOD CHAIN. Food chain deals with food not intelligence.I would say for the ocean- killer whale and land -a lion. But either way it would be homosapiens not humans.
Since technically humans are animals, then human beings are at the top of the food chain. Even though we have no natural prey like other top predators such as a lion for example, we have the superior intelligence and vast amount of resources at are disposal to survive.