In school we have all studied that most species who live in the wild, usually stick to their own kind. This happens all the time, unless the creatures are searching for food or for protection. Otherwise the animals form one kind have no reason to search for animals from another kind and associate with them.
In some situations, two species can come up with an arrangement that is beneficial for both of them. You can take the warthog and the mongoose, for example. The two mammals have very little in common, yet they share a common and unusual purpose!