Oxygen is what animals need in order for Carbon Dioxide to be exhaled while breathing. This is part of what the Respiratory System does. Carbon also enters animals that are in contaminated environments such as living next to a factory or a polluted area.
So prey is needed for a predator to eat. When there is less prey the predators community goes down as well if a group of predators die like all of them then the prey community jumps cuasing food to go down and kill everything.
