What distinction is highlighted between 'rarity' based on distribution versus 'rarity' based on population size?

A large, geographically spread subspecies might be vulnerable but not as immediately 'rare' as one confined to a few miles of stream.

It is important to differentiate the concept of rarity in native fish conservation based on two factors: geographic distribution and total population size. A subspecies, such as certain strains of Lahontan Cutthroat Trout, might maintain a large total population spread across several large lakes, classifying them perhaps as vulnerable, but not immediately 'rare.' In contrast, a fish like the Paiute Cutthroat Trout, confined to only a few miles of stream, represents the extreme end of rarity because a single disease outbreak could potentially eradicate the entire known wild population, meaning every single fish is paramount to the subspecies' survival.