I can't speak to the realism, but I love that they allow the bonus in the game. I almost always check to see which animals can go together, and quite often end up putting more than one in every habitat that will allow it.
As a game mechanic, I think of the bonus as being more about guest enjoyment (which is calculated based upon animal welfare), and/or allowing us to offset any conflicting elements of their habitats (like plant coverage or terrain paints that may be different for the two species).
I was pleasantly surprised by how many of the Wetlands pack animals had lots of interspecies bonuses, and have gone into several of my old zoos and added them in with species that I'd already built for over there.
As a game mechanic, I think of the bonus as being more about guest enjoyment (which is calculated based upon animal welfare), and/or allowing us to offset any conflicting elements of their habitats (like plant coverage or terrain paints that may be different for the two species).
I was pleasantly surprised by how many of the Wetlands pack animals had lots of interspecies bonuses, and have gone into several of my old zoos and added them in with species that I'd already built for over there.