What critical function does the lungs serve in the body?

extracting oxygen from inhaled air for distribution via the bloodstream to every cell in the body. 

The lungs' main role is to bring in air from the atmosphere and pass oxygen into the bloodstream. From there, it circulates to the rest of the body. Help is required from structures outside of the lungs in order to breathe properly.

if the hares very faster than they are now, and thus the lynx's hunting success rate drops because it will be harder to catch them, the rate that will change will be the pray-rate. the pray-rate will change because more hares will be able to survive, thus more individuals for reproduction, so the end result will be increasing population of hares.

the predator-rate will remain pretty much the same because there will be more than enough pray, but the hunting success rate is stagnant.