as much as i know, animals live in harmony with other, completely different animals in the same ecosystem
I don't think that is quit right. Have you ever seen what happens when a mouse realizes that there is a cat or an other predator around? Why is it absolutley wrong to have a ferret and a rat as pets in the same room?
It is not only stress for those animals it is abolute and pure Horror. They fear for life and though the cat might not even attack, the mouse can die just because of a heart attack.
Ferrets smell rats and rats smell Ferrets...both animals will never ignore their nature as it is supposed to be. There are a few exceptions, but these are mostly seen with pets and not with wild living animals.
There are Ferrets who will become friends with Rats. There are dogs that will become friends with a small bunny. There are Lions that will remember the human they grew up with.
But how often are there lions that become friends with zebras in their natural environment. The Fox won't stop hunting a rabbit just because it is cute. An eagle will continue hunting though the mice he kills has lots of new born babys.
This just is nature. It is not cruel nor horrible. Animals won't kill just because for fun or because they want a new part of the forrest of their own, as we humans do. They just live. And because of that they recognize the human as a predator. I don't think that a lion, tiger or even an Rhino will run of a human because of fear.
And not all animals fear humans. They know exactley when there is no harm for them. How many wild boars, foxes, racoons and birds have started to live IN human towns. Not because only there is plenty of food and nice, warm housings. No...humans just don't go over and kill them. They can also feel if a human is attracted to them and just respects them, or maybe fears them. Have you ever realized that cats often go to people which just don't like them?
Dogs too have people they like and some they don't.
There are humans that have some...bond with animals. Or better...they just understand how to behave so that animals won't fear them. It isn't helpful to squeak and cuddle. Just be quiet and relaxed, show respect and you earn respect. Something I learned over the years I live with animals and photographe them.