Dogs can't live in nature? I think that needs a citation. Or at least we need some kind of explanation for the apparently impossible phenomenon of stray and feral dogs.
Dogs with extremely flat faces (think pugs)? They have a lot of trouble breathing. Also, their eye sockets are shallow and so their eyes will pop out of the socket sometimes. There's a litany of health issues related to chasing the breed standard for dogs, sometimes related to how the standard has been taken to an extreme that deform the dog and sometimes related to the massive inbreeding that's happened as a result of chasing the breed standard.
There are certainly some dogs that can live in the wild, and there are certainly some breeders who try hard to be responsible about how they breed for the standard and how they breed their lines together, but the average purebred dog is not one you can just drop in the woods and it'll go find its own food and survive.
He fiercely guards food and will snap at anyone that reaches for him. He hunts insects including flies and cockroaches (he caught at least a few of those on our walks).
I don’t think he’d be as effective as a rat terrier, but I suspect he could hunt and kill field mice and maybe small rats.