Sum of heterogeneous blind zones predict movements of simulated groups

Simulation models regarding groups of fish and birds based on individual movement decision rules have become increasingly sophisticated. Recent studies have started to tie together how the rules of homogeneous independent-acting individuals lead to emergent group behaviors. However, there is less research on the role that heterogeneity within a group has on these emergent properties. Heterogeneity in real animal groups due to hunger, sex, body size, species, and age can influence speed, nearest neighbor distance, and viewing angle. In our study we examine how differences in viewing angle (or its complement: blind zone) within a group influence emergent properties such as group size, polarization, group shape, and segregation. Simulated groups were assembled with different mixes of blind zones (e.g. half the members with a blind zone of 60 degrees and half with a blind zone of 120 degrees). Significant differences in many of the measured emergent properties were found and were related to the level of heterogeneity as well as the absolute value of the blind zone. In homogeneous groups, increased values for the blind zone led to groups that were: smaller, more elongated, and denser. In heterogeneous groups the sum of blind zones predicted emergent group behaviors. Specifically, as the sum of the blind zones increased: group size and density decreased and the shape of the group became rounder. However, several mixes produced emergent properties that were very different than the predicted regressions. Our findings suggest that it will be important for researchers to look at how individual differences in blind zones within real groups such as fish schools and bird flocks influence emergent behaviors. Our findings also have applications to designing sensor systems for car navigation systems and robotic arrays.