Oricorio is really more of an example of adaptive radiation than ring species. But I guess with Oricorio being the same species the distinction isn't as big as it would if all 4 were separate species entirely. Maybe it'd be most accurate to describe Oricorio as a species in the middle of adaptive radiation that has yet to complete speciation.
But for a ring species, imagine a mountain. Bird A lives North of the mountain and can breed with Bird B that lives on the East. This means they're the same species. Bird B can breed with Bird C that lives on the South of the mountain, meaning they're the same species. Bird C can breed with bird D on the West of the mountain, meaning they're the same species.
But Bird D and Bird A cannot breed with each other. Meaning they are not the same species. Thus there is a ring, where if you examine most parts of it you have the same species, but when you reach the end, they're different. Its kind of like looking at a color gradient between red and white and identifying when its red, when it becomes pink, and when it stops being pink and becomes white.
Something like that would be hard to do in Pokemon I guess, since we define species by ID Number, not breeding ability. I just really like how much biology there's been in Sun/Moon, so I thought it'd be a neat concept to bring up, even if it would be awkward to actually implement.
Perhaps a better way to do it would be if say on Melemele Island we had generic Lapras. Then on Akala we had a Lapras that was still Water/Ice, but its shell was bigger and darker. Then on UlaUla we had a Lapras that was again, still Water/Ice, but its skin color became more brown than blue. Finally on Poni we have a Water/Rock Lapras. Slight variations occurred throughout, but the only mechanical difference occurred at the end of the ring. Of course feel free to replace Lapras with whatever, it probably suits a new Pokemon than an Alolan form anyway.
Oh, I see. I guess it's possible, all it would involve is messing with the Egg Groups:
- Normal Lapras is in Monster & Water 1.
- To get Lapras to a point where it can't breed with the Water/Rock Lapras it can't be either of those Egg Groups.
- Lapras 2 could be placed in Dragon & Water 1.
- Lapras 3 could be placed in Mineral & Water 1.
- Water/Rock Lapras could be placed in Dragon & Mineral