This is an awfully heavy handed question for a forum dominated by the ten to eighteen demographic.  I wonder if you should have defined 'community' since we're all taught nowadays to be individuals, to not rely on teammates, and to do our own thing.  The United States, at least, is a country of individuals striving to be their own best, not work in harmony and come together for the betterment of the world.  Community isn't something that happens all that often.

I'm willing to bet, in fact, most folks don't know many of their neighbors, certainly not in apartment buildings or condos.  You may know them enough to wave at them or pick them out of a line-up but that's as far as it goes.

So... my answer is this: Ethos goes generally out the door when people are in survival situations.  I worry about what my family is doing and how I can ensure their safety and survival.  Only then am I worried about my neighbors.  Laws and rules go out the door and it's now Warmaker's Law of The Jungle.

I challenge anyone to really experience serious problems and be different.  Does it happen?  Sure, to a tiny minority or a well-knit community that actually acts like family.

warmaker :

     I think that there would be a large difference between what happened to tiny communitees, and what would  happen people in big cities. A lot of people in cities would die first, because they are dependent upon food being shipped to them miles away. They are also unfortunatly not very self sufficient.

     In small communities, people do know each other better.
They would be affected by things, but they would be a lot more prepared. Some families, may ban together for more protection.

People of similar faith would doubtlessly work together in these things. I see city people just going plain crazy with morals. Whatever it takes to survive. I'm not talking about everyone in the city, but. . . unfortunately. . . cities seem to be more. . . carnal. . . 

Many songs about the city sing of "The will to survive" Because it is more of a jungle out there where you have to survive! I'm not saying that cities are bad, or that most people in the city are bad. I'm just saying, that they're going to get hit the worst, and the more a man is forced to do what it takes to survive, and the more he follows his instincts.