And then there are the horses: about 150 to maybe 400 of them. They have roamed the island for many generations, descended from animals deliberately put there in the 19th Century. An ever-so-romantic myth claims that they reached the island after escaping one or more shipwrecks. Either way, they are there because of human actions.
The Ipswich sparrow, once considered a distinct species, is now regarded to be a subspecies of the widespread Savannah sparrow. There may be some insects who have achieved subspecies status as well, breeding there for such a long time in isolation from their mainland counterparts that the forces of evolution have slightly changed their appearance. More than 190 plant species have been found there.
But, it is not a "pristine" environment. Sable Island has been impacted by humans for centuries. People have released cattle, horses, goats, and rabbits on the island, but most died off. This is a harsh place. The horses survived.
Recently, Sable Island was added to Canada's National Parks System. You may think that's a good thing, but it's not necessarily so. Parks Canada, the agency in charge of National Parks, is committed to maintaining "ecological integrity," which is described as the environmental conditions that are "characteristic of its natural region and likely to persist, including abiotic components and the composition and abundance of native species and biological communities, rates of change and supporting processes."