This has weakened their gene pool, making them more susceptible to disease and death. Animals can adapt in changes in the environment if they have a high gene pool. You exist at a price if you have low genetic variation. An example would be to repeat your own clone over and over. This causes a weak clone of yourself, and survival is unlikely.
Lions are also a threat to the cheetahs survival, for they kill off their young.
The cheetah can out run their prey, especially out in the open. They have been known to reach speeds of up to 70 mph, and are considered the fastest of all cats. Not being good climbers, and lack of strong muscles, they can not hide their kill in trees like other cats. When a cheetah feeds on it's kill, they usually eat it in the same spot where they killed it. Another disadvantage is their claws do not retract.