I've read, but not verified, claims that many farm animals would be extinct or close to extinction if we didn't actively maintain their population (for purpose of slaughter), as we've taken over their natural habitats.
There are small select herds of wild bison in protected areas, and I imagine that would be the case even without ranching. But these bison herds are often carefully managed, as else wise the herd population would start to conflict with ranchers and farmers surrounding the protected areas. (This is the case with the Yellowstone bison herd for instance -- https://www.hcn.org/articles/the-science-behind-yellowstones... )
The bison population has grown from near extinction in the early 20th century to roughly half a million today. About 96% of these half a million bison are bred for consumption by humans. ( http://www.pbs.org/wnet/need-to-know/five-things/the-great-a... )