Oasis Cay used to be a flourishing island full of all kinds of life. Human and Pokemon alike. Until one day an unknown accident almost completely destroyed the population. With time the human population recovered, but the pokemon population didn't. It seemed like the pokemon were slowly disappearing. Oasis Cay's people believed that the pokemon population would restore itself so they continued building up Silene City, and eventually established Zinnia Town.
As for the Pokemon their numbers kept getting lower and lower. It would have totally vanished if it wasn't for Professor Magnolia and her team stepping in. With a majority of the island unused they established a reservation, and started to make moves of preserving the current population.
It took a lot of time to keep the pokemon population from decreasing. After five years they managed to get positive numbers for the first time. After that, things were going well for the reservation. It was a slow up hill battle, but it was still going well.
The brings us to where we are today. The Flora Pokemon Reservation have finally declared pokemon numbers steady enough to allow the population of Oasis Cay to get their own pokemon! Granted it takes an application process for a citizen to get one but it's all worth it in the end.
Now help the new trainer population and system get established! Or follow a different path than what ten years in other regions want to follow. Learn to become a researcher, or study medicine. Maybe you would like to help the rangers keep a handle on the wild pokemon, or you want to help increase the population by becoming a breeder. It's your path to choose!