These images come from a journal article that documents a red fox killing an arctic fox at Prudhoe Bay, Alaska, where both foxes are relatively common– and happen to share space. However, one of the rules about wild dogs is that a larger wild dog species will kill a smaller wild dog species that shares the same habitat. It happens with coyotes and wolves, golden jackals and wolves, and African wild dogs and black-backed jackals. Black-backed jackals dominate side-striped jackals, but in general, the larger species tends beat up on the smaller one.
Red foxes dominate other fox-sized canids in their range– with one notable exception.
Red foxes avoid Urocyon gray foxes. As the son of a son of an old fox trapper and caller, I was always told that a gray fox could be caught on a trap that had been marked with red urine, but you would never catch a red on trap marked with gray urine. If one were calling foxes to the gun, both species could be brought in on red calls, but only grays will come to gray calls.
When a gray fox was put in a run with several urine producing foxes, it instantly attacked all of its red kennel-mates and had to be removed before it killed them.
Red foxes don’t do to gray foxes, which aren’t actually foxes, what they do to arctic foxes.
Red foxes and gray foxes are about the same size, at least in the areas where they share range in North America. Red foxes in other parts of the world are indeed quite a bit larger.
Coyotes dominate and eat both species, and if they see a toy poodle, they think that’s just a fuzzy little fox with a bit more fat on it.