I cannot think of a one word antonym (word with the opposite meaning) to "disperse". However, to disperse some "thing" means to distribute that thing widely. Thus, a group of people can "disperse"...
Burrs, which are seeds with rough hulls that have projecting spikes or hooks, use the projections to "latch onto" passing animals or people. The seeds then "hitch a ride" on these passers by to...