No. If they could find one they probably would eat them but there are no tigers in Australia (outside of Zoos) and no Platypuses in Asia (outside of Zoos).
A white tiger is a carnivore so it eats meat probably from small to medium sized prey and from what I recall nothing eats tigers besides some very brave humans.
If a female tiger has had cubs then the cubs are in risk of being eaten by an adult male tiger. The male tiger will eat the cubs so then the female tiger will become in heat again as she won't have...