Free choice post- story ideas

I want to write a story about lions living in the Ngorongoro crater in Tanzania. I am reading "Things Fall Apart" right now and I have had this idea in mind ever since I saw an episode of PBS's Nature about the lions. The show told the story of one lion pride that had almost been wiped out by sickness in the 1960s and had suffered the effects of inbreeding ever since, being more susepable to disease. They were also threatened by hyena competition and most of all competition from another pride of lions. This other pride was coming in to take over their territory. I have done a little research on the lions, and I am wanting to write maybe a tragedy from the perspective of the aging patriarch of the pride. He gradually loses his hold on the pride until he is driven off by the rival males so that they can mate with his females. He goes off injured to wander until he finally dies from hunger. I am not sure how to organize this kind of story. I don't just want to rip off what I saw on "Nature," but I am interested in the story and the themes that it shows of pride, fate, power, and the pain that comes with necessary change. I don't know if it could fit into a short story, or fill up a novel, or if I should work on some kind of an epic poem.