Communicative exchanges consist of both static and dynamic structures that can be used for prediction. Temporal dynamics are often neglected in communication studies. We used Shannon mathematical theory of communication to examine 1,594,690 contributions from 206,184 contributors to 38 open online collaborations. We found that about three-fourths of the total predictability of turn-taking stemmed from participation frequencies (static variance), while one-fourth originated from the temporal sequence (dynamic process). Most dynamic structure is contained within consecutive dyads. We found a trade-off in the importance of static and dynamic structures, and also found that static structure was predicted more strongly in a stationary process and dynamic structure in a nonstationary process. We offer a combination of both theoretical and empirical factors to explain these findings. These findings have implications both for theorizing and methodologically measuring communication as a dynamic process, as well as for the practical design of online collaboration systems.