Before European settlers came to North America, wolves ranged across the continent. Larger and stronger than coyotes, they were able to compete well for food and territory. The coyotes had a difficult time competing for the same habitat. Coyotes therefore had a limited realized niche.
Eventually, American hunters wiped out the wolf populations in places such as New England and New York.
Coyotes, better able to coexist with humans, have moved into habitats the wolves have been evicted from. Enjoying a wider range, their realized niche is now much larger than before.