On to the Pokémon now - the really interesting things!
All wild Minami Pokémon are native to the island. Most other Pokemon from elsewhere (eg: Tropius from Hoenn, Rattata from Kanto etc) are owned by humans. It's illegal to release them into the wild, in a strict attempt at keeping all the ecosystems and the web of life as constant as it was before humans arrived. So generally, it's a given fact that every single Minami Pokémon can't be found anywhere else on any other island (i.e: they're all pretty much native to Minami). There are bound to be similarities to other more well-known Pokémon, because of the discrepancies of time, and because of something called 'divergent evolution'.
Divergent evolution has nothing to do with the other 'evolution' in the Pokémon world, save the fact they share the same name, and is only a theory (it is important to be aware of the continuing feud between the theory of evolution vs the theory of intelligent design, especially since this has also now cropped up within the Pokémon world itself!). Anyway, the theory states that if one single species (for example, a Shellos) is 'diverged' (that is, split into two separate groups), each group will each change slightly over a long period of time in order to adapt to their new environment (which is why you get two differently coloured/formed Shellos). Eventually, you may get two species, still metaphorically able to interbreed, but with obvious differences physically and physiologically. </biology lecture>
One other important thing to add is what happens when you turn 13 - you get your own Pokémon. No, it's not at the age of 10 any more. The legal age was bumped up a little after the dangers of the island were assessed. In a special traditional ceremony, Trainers gather from all over the region at Basil Town, where the person in charge will be able to give them a choice between not only 3, but 12 different Starter Pokémon. This allows Trainers who want to concentrate on battling with specific Elements the chance to keep their own original Starter in their team, after Hoennean statisticians became worried about the fact their own graduates seemed to be dumping their Treecko or Mudkip in a Box once 'unneeded'.
When you're deemed suitable to become a Trainer (normally at the age of 13, although this is partially determined in a test evaluating your knowledge and your personality) you can take part in the ceremony held down at Basil Town. Trainers flock from all parts of Minami to get their 'Starter'. This is the only place you can get them from. Normally the person in charge is of a high standing in the biology field of work (a Professor, for instance).
Unlike other regions, Trainers are not shunted into choosing one out of three types (Grass, Water and Fire being the norm), and are able to choose from a selection of twelve different Starters; practically none of them with hybrid Elements (so nothing gained if you wanted to get one with two Elements) and all with two evolutions. Take Splascade for instance. Its entire family is Water, and it evolves into Sycloon, then Stornmado. The only Starter with a dual Element evolution is Freeliz the Ice Starter. Ice is a Sub-Element (it's basically frozen Water) and Dragelid is both Ice and Flying. Then again, Freeliz's entire family are quite rare and as such you can only Start with one by special request.
