I read about a similar study in college involving rats. Increased population density led to deviant behavior and violence.
Without any studies at all, I observed how much nicer everyone in our office was, and how much calmer the environment, when several people were out on any given day.
I should have pinged you to my reply #98. I linked a fascinating article talking about the mouse study.
http://www.freerepublic.com/focus/news/3645639/posts?page=98#98
I don’t know if the link will work.