This is something Danielle and I talked about as well. Especially when you consider Academia - I mean, if they can build that incredible city (not to mention a second Cocoon), what's stopping them from making more cities throughout Pulse?

The key thing for me would be the creatures that live on Pulse. And I think the best display of this environment would be New Bodhum, during the attack by those creatures. Basically, outside of Academia, there aren't enough soldiers to take on the beasts in the wilderness. Unlike the beasts on Earth, these monsters can rain magic down on you.

There is, of course, also the fal'Cie. While dead on Cocoon, they are not so dead on Pulse. So even if they did slowly pin down some safe countries throughout the world - enough to supply them with the food needed - then who's to say that some fal'Cie won't come along and turn half the population into Cie'th and/or l'Cie? I'd say pretty slim, really. After playing through FFXIII I think a big lesson learned was "fal'Cie are not to be trusted and they do act in their own interests." Just one 'evil' fal'Cie is enough to turn an entire city to Cie'th for all we know. I mean, Titan is there purely to produce more powerful creatures. So either you get more and more powerful wildlife or you take on a fal'Cie the size of a mountain. Good luck!

As for the ecosystem and all that, I'm certain with the technology that they have that they could easily replicate most of the things that the fal'Cie provided, such as light and food and whatnot.