If the Tiger is introduced to Africa it will affect the ecosystem, no doubt about it, Ron Julie demonstrated that very clearly. The Tiger is a faster stronger cat than the Lion, and unlike the Lion the Tiger isn't any abit afraid of water, it infact thrives in water.
At the end of the vid on Youtube you will see the people behind the experiment picking up and loading the dead Gazelles that Ron Julie killed on their first go at a Gazelle herd. In the end there simply wasn't room for them all.
However it has been proven that hundreds of years ago there were Tigers in Africa, and Lions were more widespread as-well, so there's no doubt that these cats are very adaptable.