Answer:
Without predatation, things wouldn't eat each other.
Rabbits won't eat grass, Wolves won't eat Rabbits, and so on...
If it were to continue this way there wouldn't be a single animal on this planet. (everything living except plants that only rely on the sun.)
It's a food chain. A CHAIN. Each varible depends on each other.
And a food chain has a direct impact on the ecosystem.
For example:
No rabbits mean there is so many grass and carrots left behind
No wolves means there are too many rabbits
So that means
No wolves
Whatever eats the wolves wont be alive
Whatever eats THAT wouldn't be alive