As telecommunication networks become more common, there is an increasing interest in the factors underlying the development of online social structures. It has been proposed that these structures are new forms of organizing which are not subject to the same constraints as traditional social structures. However, from anecdotal evidence and case studies it is difficult to evaluate whether online social structures are subject to the same problems as traditional social structures. Drawing from prior studies of traditional social structures and empirical analyses of longitudinal data from a sample of Internet-based groups, this exploratory work considers the role of size and communication activity in sustainable online social structures. A resource-based theory of sustainable social structures is presented. Members contribute time, energy, and other resources, enabling a social structure to provide benefits for individuals. These benefits, which include information, influence, and social support, are the basis for a social structure's ability to attract and retain members. This model focuses on the system of opposing forces that link membership size as a component of resource availability and communication activity as an aspect of benefit provision to the sustainability of an online social structure. Analyses of data from a random sample of e-mail-based Internet social structures (listservs) indicate that communication activity and size have both positive and negative effects on a structure's sustainability. These results suggest that while the use of networked communication technologies may alter the form of communication, balancing the opposing impacts of membership size and communication activity in order to maintain resource availability and provide benefits for current members remains a fundamental problem underlying the development of sustainable online social structures.

Online discussion communities have become a widely used medium for interaction, enabling conversations across a broad range of topics and contexts. Their success, however, depends on participants' willingness to invest their time and attention in the absence of formal role and control structures. Why, then, would individuals choose to return repeatedly to a particular community and engage in the various behaviors that are necessary to keep conversation within the community going? Some studies of online communities argue that individuals are driven by self-interest, while others emphasize more altruistic motivations. To get beyond these inconsistent explanations, we offer a model that brings dissimilar rationales into a single conceptual framework and shows the validity of each rationale in explaining different online behaviors. Drawing on typologies of organizational commitment, we argue that members may have psychological bonds to a particular online community based on (a) need, (b) affect, and/or (c) obligation. We develop hypotheses that explain how each form of commitment to a community affects the likelihood that a member will engage in particular behaviors (reading threads, posting replies, moderating the discussion). Our results indicate that each form of community commitment has a unique impact on each behavior, with need-based commitment predicting thread reading, affect-based commitment predicting reply posting and moderating behaviors, and obligation-based commitment predicting only moderating behavior. Researchers seeking to understand how discussion-based communities function will benefit from this more precise theorizing of how each form of member commitment relates to different kinds of online behaviors. Community managers who seek to encourage particular behaviors may use our results to target the underlying form of commitment most likely to encourage the activities they wish to promote.

Leaders of robust, sustainable virtual communities find ways tostrengthen their members' sense of social identity and motivate their participation in the community's activities.

Online relationships are less valuable than offline ones. Indeed, their net benefit depends on whether they supplement or substitute for offline social relationships.

No abstract