Buddhism vs. Nature and Real World
Samsara can be quite brutal and there is suffering. The Buddha acknowledged this in the First Noble Truth. And his last words urged his disciples to strive on with diligence toward their enlightenment. Only through Nibbanna will one escape the suffering of Samsara.

Nature is full of examples of suffering such as you detailed. The animals involved have no evil intentions. They simply eat to stay alive. This is why humans are so very fortunate. We generally don't have to live such a brutal life and we can think things through and form intentions and take actions with as much wisdom and compassion as we possess. This is a blessing.

Treating all beings with metta (loving kindness) creates peace in one's mind. Treating other beings with cruelty creates conflict and discord in one's mind. One is clearly better than the other for living a peaceful life and for creating better conditions for one's meditation and eventual enlightenment. 

A sutta which explains this idea of taking care of others by taking care of yourself is the Sedaka Sutta. SN47