Eat or be eaten, it is the principle of the food chain. An animal eats another, which eats another, and so on.
If this balance is broken, it is a whole ecosystem that can collapse.
However, you need to know that to survive, a being can eat another only if it is smaller than him. An Ant will not deal with a whale, it's obvious!
In the food chain games, you have to eat the smaller creatures than you. You can enlarge and eat larger creatures.
Be careful, there is always a bigger creature than you, which will not hesitate a single second to eat you! You will need to avoid this creature.