A short story usually takes place during a smaller time period than a novel and usually deals with one major conflict. The rising action, climax and plot resolution occur rather quickly. Additionally, a short story usually has a minimum of characters and focuses usually on one of the characters instead for example, a whole family.
In a short story, the main character's transformation or 'revelation' as it is sometimes referred to, occurs in the resolution. The character has learned something about himself through the events that have transpired. In a novel, this process may take longer and may be a combination of experienced events which lead to the transformation of the main character.
This is not to say that short stories are less complex or somehow a lesser form of a novel, but they do differ usually in the pacing of the story: the way in which the rising action occurs and the resolution of the conflict.