To be honest if prey were smaller than tigers they would totally be extinct because without all that prey to eat/kill and etc, than tigers would starve to death and die, or just start maybe eating each other because there is no more prey around to eat. Tigers like to eat those weak, vulnerable animals because they're easy to prey upon, so without those weak ones, it may be harder for them to prey upon the strong prey because they may not go down as easy so this can really affect the tigers badly.