Richard Parker, the adult Bengal tiger who ended up in the lifeboat with Pi, helped keep Pi Patel alive in many ways in Yann Martel's novel Life Of Pi.
One way Richard Parker contributed to Pi's survival is by ridding the boat of another predator. The tiger is responsible for killing the hyena. The hyena is a predator who surely would have killed Pi had the tiger not gotten to him first. In point of fact, the only reason Pi is not in danger from Richard Parker at the beginning is that of the tiger's seasickness. In chapter 53, Pi describes the demise of the hyena at the hands of Richard Parker:
"Richard Parker had risen and emerged. He was not fifteen feet from me. Oh the size of him! The hyena's end had come, and mine . . . the flame-coloured carnivore emerged from beneath the tarpualin and made for the hyena. The hyena was leaning against the stern bench, behind the zebra's carcass, transfixed. It did not put up a fight. Instead, it shrank to the floor, lifting a forepaw in a futile...
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