There isn't a single definitive, validated, model that explains community behaviour.
However, the most popular models are coalescing around similar topics.
The BJ Fogg model, discussed here, sees participation through the prism of motivation, ability, and triggers. You need members motivated to participate. You need to make participation very simple. You need triggers that prompt members to participate.
You can apply and test different aspects of this model to sustainable increase the level of growth and activity in a community.
Another model is the Triandis model (pictured below).
If we apply this to communities, we can say participation is shaped by 8 broad factors;
1) Do I believe my participation in a community will have an impact?
2) Did my previous participation have an impact?
3) Do people like me tend to participate in this sort of community?
4) Does my role within this topic induce me to participate? Am I expected to participate?
5) Will participating in this community help me achieve my personal goals?
6) Am I emotionally provoked into participating?
7) Have I participated many times recently?
8) Is there anything in my environment (or on the community platform itself) which may prevent me from participating?
A community scientist would look at these models, look at the research, and figure out how they can be measured (attitude, social factors, affect, past behaviour, intentions) and then put in place a practical plan to address each of these issues.
You can target specific interventions at specific people to achieve the desired result of more activity from your existing audience. You can diagnose exactly what is going wrong. But you can only do this if you have a behaviour model you can work from.
This is the new level we need to be operating at. Scanning through the existing community groups today, the discussions are beginner at best; Should my brand use Pinterest/Instagram? What listening tool should I use? Where can I find a community job? Should I let companies sponsor my community?
This is why we invite you to attend the Virtual Community Summit in London this February 20 - 21. We're going to take the first steps to converting community managers into community scientists. We hope you will join us.
If you can't make that, consider joining CommunityGeek; a community for people looking to master the science behind communities.