I don't argue about definitions. If you (*) want an idiotic definition of "species" that makes taxonomy dependent on sexual behavior, go ahead. The human homosexuals will be ecstatic. I am here to tell you that a boundary exist, -- no matter how fast you move definitions, -- which cannot be crossed through random mutations. When you see the light, -- or rather the dark hole that evolutionism is, -- you can call that boundary Annalex. It kind of sounds Latin, doesn't it?
why would they "need to"?
Because their hypothesis and cult object is that species evolve from other species in a way that the new species is, overtime, radically different form the original: does not produce viable offspring even in a lab, looks different, -- like an elephant and a manatee. Not like zebra 1 and zebra 2 that you consider a proof of something.
will you accept as a serious answer the definition of "non-manatee": any creature which cannot successfully interbreed with wild manatees?
If you followed and understood the objection to the evolutionary hypothesis you would know the answer. The non-manatee must not interbreed with a manatee even in a lab, but interbreed and produce viable offspring that does likewise, with the new species of non-manatees. To have a different look and behavior, -- remember, the claim is that evolution produced such visibly different creatures as manatee and an elephant and a hairy rat, -- would be nice too.
Hypotheses need an experimental proof, -- that's what makes storytelling a science.
Good luck.
(*) Nothing personal. "You", not "thou". You were not expressing any individual research here, did you?
And you define this alleged "boundary" as what, exactly?
And your physical evidence for this supposed "boundary" is what, exactly?
And your scientific hypothesis which explains why there should be such an alleged "boundary" is what, exactly?
And your scientific confirmations for this hypothesis, confirmations which could turn it into a recognized scientific theory, are what, exactly?
And the names of the scientists, and their scientific qualifications, who found the physical evidence, proposed the scientific hypothesis and then confirmed it, are who, exactly?
And the peer-reviewed scientific literature reporting and discussing this amazing "boundary hypothesis" is to be found where, exactly.
Of course, the real answers to all those questions are "none", "nobody" and "nowhere" because, because, because this alleged "boundary" is not scientific at all, it's a religious idea.
Isn't it, FRiend?