shouldn't we restrict the artificial term 'species' to organisms which can
only breed within that species?
That is only part of the definition of a species, & is largely ignored
nowadays.

shouldn't we use the word specie for one species
Absolutely not. The term specie refers only to currency. In biology, species is
both singular & plural, like thrips & a few other words.


Iris,
Central NY, Zone 5a, Sunset Zone 40
"The trouble with people is not that they don't know but that they know so much
that ain't so."
Josh Billings (Henry Wheeler Shaw), 1818-1885