Differences between short & feature films

"What are the key differences in narrative between short films and feature films?"

I would say that - due to the difference in length - feature films can have many different characters, scenes and storylines, whereas short films tend to have far fewer, or even just one of each. Both do, however, normally have a beginning, middle and end (at least to some degree). There is normally some kind of change in character and/or situation over the course of the film, regardless of length. Characters almost always have clear goals, motives and weaknesses, and there is normally an antagonist of some sort. This does vary greatly, however, as short films can vary greatly in length. A short film which is almost half an hour long may well have lots of scenes and characters and can almost feel like a feature film in itself.