Awareness
Imagine the sudden discovery of a completely new world, inhabited by creatures we never knew existed. It sounds like a scenario from a science fiction movie.
Meanwhile, similar scenarios might be unfolding right before our eyes. More than likely, invertebrates living underground have never seen a bird.
Every layer of the forest has its own inhabitants. It's possible that some organisms will never encounter those from a different layer. Yet, together they form the forest as a whole—not always aware of one another's existence.