Yeah, people like to put things in organized little boxes...and that's not how the real world works when it comes to species differentiation. Many of the species we have classified, if you were to DNA profile them, would actually be the same species but with different social behaviors or geographical distribution which prevents crossbreeding without human interferance.
There has been a huge deal about this in the cornsnake community. Cornsnakes, and all other new world rat snakes hybridize very readily in captivity, have fertile offspring, and after a few generations of crossing it's impossible to tell whether an animal is a hybrid or not. A few hybrids happen in the wild, but due to differencea in breeding seasons and courtship rituals it's not terribly common.
Then you have kingsnakes (lampropeltis), a totally different genus with totally different behaviors, most notable being cannibalism. They also produce fertile and hardy offspring with rat snakes in captivity. It would never happen in the wild, because they would normally eat a rat snake. In captivity you have to "bait and switch" lol, and even then it's a bit risky. People still do it often though, and after a couple of generations it's visually impossible to tell a hybrid from a pure animal (which is bad when you have a snake that you expect to cohabit peacefully with others, and then starts eating them for no apparent reason).
All of this applies to different species of trout, salmon, grouse, deer.
Let's not even get into plants. lol!
If it weren't for all the political/ethical ramifications, scientists would have different races of human all classed as different species. When you look at the phenotypical difference between a norseman and a member of the hottentot tribe...there is a greater difference than between a wolf and a coyote.
In fact "back in the day" people
were classified as different species (which a lot of jerks used as an excuse to treat people badly)