People define species to fit the needs of their ideology. Evolutionists would expect a rather fuzzy definition. Darwin said he had come to regard species as just strong varieties. So it is not surprising that evolutionists regard the species boundary as anything that, in the wild, results in groups not intermating.
Whereas creationists, seeing a need to explain observed variation among living things, regard species as comprising all individuals that are biologically capable of mating with fertile offspring, regardless of what happens in the wild.
It is interesting that even this position has fuzziness, because there are varieties where interbreeding produces some fertile offspring and some infertile. Actually, there are humans with atypical chromosome counts, some of whom can have childrem.
Humans love to categorize things. It makes thinking easier if one can create convenient huristics instead of dealing with everything one at a time. I'm gonna have to whisper this but sometimes stereotypes aren't bad.
The definition of species is like that. To draw an analogy that will be missed by the people who need it most, if you wake up one morning and it's 55 degrees outside, and by mid-afternoon your thermometer reads 95 degrees, at what temperature would you say the day went from "cool" to "hot"?