In this paper, we address the following two questions: (1)How does a participant’s membership decision affect the others (neighbors) with whom he has collaborated over an extended period of time in an open source software (OSS) network? (2) To what extent do network characteristics (i.e, size and connectivity) mediate the impact of external factors on the OSS participants’ dynamic membership decisions and hence the stability of the network? From the Ising perspective, we present fresh theoretical insight into the dynamic and reciprocal membership relations between OSS participants. We also performed simulations based on empirical data that were collected from two actual OSS communities. Some of the key findings include that (1) membership herding is highly present when the external force is weak, but decreases significantly when the force increases, (2) the propensity for membership herding is most likely to be seen in a large network with a random connectivity, and (3) for large networks, at low external force a random connectivity will perform better than a scale-free counterpart in terms of the network strength. However, as the temperature (external force) increases, the reverse phenomenon is observed. In addition, the scale-free connectivity appears to be less volatile than with the random connectivity in response to the increase in the temperature. We conclude with several implications that may be of significance to OSS stakeholders.