This paper investigates the sustainability of a type of digital ecosystem, namely, knowledge-sharing communities built on the wiki model. Sustainability is hypothesized to result from the participation of contributors with varying levels of resources and interests. The differences in resources and interests, according to the critical-mass theory, enable such communities to overcome typical start-up and growth problems. This paper describes a preliminary empirical test of the critical-mass theory in this context, with Wikipedia as a test case that demonstrates sustainability as well as resource and interest heterogeneity, based on a survey of 78 Wikipedians. The characteristic patterns of success exhibited in Wikipedia are expected to inform the management of other wiki-based information assets.