http://www.youtube.com/watch?v=fAoszVLRP6U
When it comes to competition for food wolves will kill coyotes and coyotes will kill foxes. Here is a clip Warning it is graphic but it shows how serious competition for food among canine species is. I have seen fox tracks in areas where there are many coyotes but very few compared to areas where there are very few coyotes. The majority of foxes usually move on to other feeding grounds when the coyotes move into their area.