Watching large schools of fish maneuver with the grace of a water ballet leads to an obvious question: How do so many animals spread over what is often many yards coordinate their activities with such precision? They keep an eye on their immediate neighbors. However, how many neighbors they watch is a matter for debate, at least for now.
Scientists have simulated the patterns created by fish, birds, bacteria, and other living organisms that move in groups. Typically, these computer simulations treat the creatures like magnets, their movements akin to "forces" that pull to keep the group together and push to prevent individuals from running into each other. Few studies, though, have looked at individual animals within the group to tease out the behaviors that give rise to these forces.
To see things from the perspective of a single fish, one group of researchers filmed and tracked groups of mosquitofish swimming around the edge of a tank in the lab. The researchers used neural networks, a technique inspired by the human brain for finding patterns, to analyze how each creature responded to other fish surrounding it. Their conclusion -- fish focused on their nearest neighbor.
In contrast, another group of researchers found that pairs of interacting fish might not be enough to explain all the patterns observed in schools. Watching golden shiners swim, these researchers found that fish in groups of three also seemed to coordinate their movements with one another.
Not surprisingly, there is probably no universal number. Previous studies have suggested that pedestrians choose their paths based on two or more neighbors when moving in a crowd. In contrast to the fish studies described above, observations of starlings suggest that they watch six or seven other birds when flocking.
Are these differences reflective of brain size? processing capacity? evolutionary pressures lost to the sands of time? As they say, stay tuned.
The two fish studies can be found at http://www.pnas.org/content/early/2011/11/02/1109355108.full.pdf+html and http://www.pnas.org/content/early/2011/07/26/1107583108.full.pdf+html.