Rather than splitting hairs over such issues, let's just accept that there are going to be ambiguous cases, and move on to more important issues. Ecological species concept. A finch with a smaller beak has the opposite traits. A cat like a cheetah that is fast enough to catch gazelles won't be big and strong enough to catch wildebeest. A cat like a lion that is big and strong enough to catch wildebeest will be slower and clumsier and poor at catching gazelles.
Reproductive isolation defines species.
A species consists of groups of interbreeding natural populations that are reproductively isolated from other such groups. They produce offspring, but the offspring are sterile If any of the above operates, it is called a reproductive isolating mechanism. But the ecological concept also has some advantages It is more relevant to asexual species. The biological concept seems to imply that each new mutation in an asexual organism creates a new species. At least some asexual groups seem to form discrete and coherent species, and it can't be sexual reproduction flow holding them together.