>>58281690>>58280967>>58270415I've already given part of my own explanation here:
>>58281604 but since this is an autistic niche interest of mine I'll defend my case a little more.
Nidoran, Nidorino, and Nidorina, are all on the smaller size. They start out about as small a rabbit and eventually become pig sized in their 2nd form. The first two stages are probably primarily 'opportunistic' omnivores: mostly eating whatever forage (fruit, nuts, mushrooms, digging tubers), supplementing their diet with carrion, abandoned kills, and the odd unfortunate smaller pokemon. The first two stages are also clearly prey animals (their poison-type is defensive) and probably get eaten by the numerous flying types across Kanto.
Nidoking and Queen though I think are both very rare/uncommon, can eat whatever they want in large quantities (and might be more of an ambush/kill thief type of predator), and I think they're simply too bulky to be *prey animals anymore. Combine this with the densely forested, semi-tropical, mountainous regions of Kanto and I'd expect Nidoking/queen to have the potential to get pretty large.
*I've had some time to think about it, but the Nidoran-line and the Rhyhorn-line are probably capable of co-habitation via niche partitioning "they eat different, but similar, things". The Rhyhorn-line is entirely herbivorous: Rhyhorns are grazers, with Rhydons being mixed browsers, I think Kangaskhan might be as well.
