Wikis are collaborative platforms enabling collective elaboration of knowledge, the most famous and possibly the most successful thereof being the Wikipedia. There are currently plenty of other active open-access wikis, with varying success: some recruit many users and achieve sustainability, while others strive to attract sufficient active contributors, irrespective of the topic of the wiki. We make an exploratory investigation of some factors likely to account for these various destinies (such as distinct policies, norms, user incentives, technical and structural features), examining the demographics of a portion of the wikisphere. We underline the intertwining of population and content dynamics and emphasize the existence of different periods of development of a wiki-based community, from bootstrapping by founders with a pre-established set of rules, to more stable regimes where constant enrollment and training of new users balances out the occasional departure of more advanced users.