The effect of population size and number of influential neighbors on the emergent properties of fish schools

Our results show that all group properties examined are strongly influenced both by population size, and by the number of influential neighbors. We also found a very strong interaction between the two factors: when the factors were similar, each individual responded to the exact same set of other animals, and fish schools remained relatively static, milling about in a disorganized fashion. When the local population size far exceeded the number of influential neighbors, each fish took cues from a different set of neighbors, which resulted in more mobile schools. With too many influential neighbors, group structure broke down, presumably because individuals were unable to solve the spatial problem of too many competing influences. Our results demonstrate that examination of a large state space with a wide array of metrics can shed light on the strength and combination of parameters necessary to induce specific types of gregarious patterns. Furthermore, our results suggest that, by regulating the number of influential neighbors to which they react, fish may be able to modulate group properties such as group size, speed, and polarity.