The correct answer to this open question is the following.
Using the contingency model, Fiedler would have recommended Dave to use a Laissez-Faire Leadership style, due to his weak position in the group. In this scenario, the leader does not really lead the team. The ones who really lead are the members of the group self-direct the team.
We are referring to the Flieder's Contingency Model, created by Fred Flieder at the beginning of the 1960s. Fiedler concluded in his study that there is no single form of leadership that fits every situation. What he thought what that depending on the specific situation, the leader could assume of the leadership's styles such as the mentioned above or the Transformational Leadership style, the Autocratic style or the Democratic style.