I'm trying to remember the name and author of a short story. This is what I recall of the plot:
A transport/bus breaks down traveling between two cities in an implied post-apocalyptic setting. It's revealed that packs of dogs control the countryside, they round up the passengers and break them into two groups - breeders and non-breeders. They seem to do this by scent. Non-breeders include the elderly and at least one gay character (one of the guards). The dogs seem more intelligent than normal, it's not revealed why. The breeders are then allowed to be rescued, while non-breeders are taken by the dogs - presumably as food.
There's an implication that this is a standard arrangement, that the dogs basically let humans continue to exist because we serve as an occasional food source.