Bullies and Boundaries in the World of Wild Dogs

From The Velvet Claw: A Natural History of the Carnivores by David Macdonald:

The general rule is that larger dog species dominate, or even kill, smaller ones. Gray wolves chase and kill coyotes, coyotes kill kit foxes, golden jackals kill red foxes, and red foxes kill arctic and gray foxes.

The arctic fox's range forms a circumpolar ribbon to the north of the red's, the two species overlapping in the Eurasian and Canadian tundra. Both species are impressively adapted to the cold, and are remarkably similar in everything they do. As a result, when they meet, red foxes seem to treat arctic foxes as smaller, and thus inferior, copies of themselves and overpower them. However the heavier red foxes need to eat far more and, towards the north, food becomes too thin on the ground to sustain them. The larger body that allows the red fox to bully the arctic fox further south gives it an appetite that cannot be satisfied to the north. So, the red fox's brute strength sets the southern limit to the arctic fox's range, while its hefty appetite sets its own northern limit.

Red foxes and gray foxes can occupy the same habitat (sympatry) based on the difference in the space between the canine teeth, thus, different prey.

• Related Links:
  ** Running With the Fox by David Macdonald