Much of what determines the effectiveness of a community is the level of trust and cohesion in it, communities with members who cannot rely on each other to fulfill their responsibility to the whole of the group cannot achieve their mutual goal as easily. This means that until enough of the individuals of a community have developed strong relationships with each other or shared several bonding experiences communities are quite chaotic, and finding members willing make sacrifices for the good of the group are very rare. Eventually this can be overcome without conscious effort as the individuals start to see evidence of how much they need to rely on each other, and how much their comrades rely on them, and start to take bigger risks and contribute greater efforts with the idea of the groups benefit rather than their own. Communities at this level have higher levels of survival and success for both the community and the individual, as many people are willing to step in and assist each other when they see fellow members suffering. However, communities with this level of support often take longer to form, as it takes shared experiences to form an emotional bond; these communities also have a higher standard for true membership, they may accept new people in a superficial manner, but they will often not trust this new member without considerable reason or need.
Communities will often have a specific way of choosing their membership, usually centered on how they were formed. Geographical communities will encompass everyone in the given area, however, these communities can often be very critical of new members, as geographical communities have a higher tendency to go long periods of time without experiencing any new members. The smaller the community is the more likely this is to be the case, as all of the members will recognize someone new. Cultural communities are different in the fact that they are much larger, and often have more specific requirements for membership. However, these communities can sometimes be quite easy to join, assuming you fulfill some physical requirement (usually based on race or ethnicity), and sometimes even these can be ignored if enough other requirements are fulfilled. Finally there are communities that develop around highly specific goals, cultural and geographic communities are designed to limit their membership based on boundaries that aren't very static, whereas goal-oriented communities only require that new members contribute to the goal the community is focused on, and restrictions will only be made to reduce behaviors that inhibit the goal. A goal-oriented community is the one most likely to follow the growth outlined in the previous paragraph, due to the fact that the creation of new goal-oriented communities are far more common than new cultural or geographic communities. Goal-oriented communities are also have the shortest "life-span" by far, primarily because they no longer have a purpose after either completing their goal or finding that they are incapable of being more successful in a group than tackling the problem as individuals.
There, I sat down and cranked that out a day early, aren't you proud of me. As usual feel free to leave any questions, corrections, or advice in the comments section, or e-mail me through my profile. Next I should be posting my opinion on the Core Theory presented by Robert Sagel, I know I was going to talk about hive minds, but I do lie, and I need to do some more research first anyways. Besides considering it is currently between the Halloween and the solstice I think this is the perfect time to examine the concept that defined almost an entire generation of bloggers.
See you around