Characteristic spatial distributions of velocities, as obtained for different combinations of and .

<p>Top row depicts results for , while bottom row features results for . Irrespective of , it can be observed that for the whole population essentially becomes a swarm in that the velocities of all players are much the same and close to zero. The fact that the prevailing velocity is close to zero simply reflects that the stationary state has been reached by means of adaptive, locally-inspired and slow strategy changes (which are, however, very effective even if the temptations to defect are strong). For , however, only isolated clusters can be considered to act as swarms, while the majority of players cannot be associated with any kind of group dynamics and is simply caught in the futile pursuit for the highest, yet for the majority unattainable, payoffs. These results indicate that swarming is an important agonist that promotes cooperation at high temptations to defect (see results presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0021787#pone-0021787-g001" target="_blank">Fig. 1</a>). The color encoding, as depicted right, indicates the values of for each individual player, where was chosen sufficiently large such that the stationary state of the game has been reached. Importantly, we note that for the stationary state has in fact been reached, although at a given instance in time the average velocity in the population might be different from zero.