FIG. 2.

Water flow, but not vegetation is a predictor of collective behavior. (A) Groups in flowing water changed leadership more than groups in still water. We found no evidence of an interaction between vegetation and flow or a main effect of vegetation in our two-way ANOVA. (B) Groups in flowing water fission–fusion more than groups in still water. There was not a significant of main effect of vegetation or an interaction between vegetation and flow. (C) Groups in fast-flowing water with minimal vegetation (FM) were more cohesive than the other groups, which led to a significant vegetation by flow interaction, and main effect of flow. The main effect for vegetation did not reach significance. (D) Groups in fast-flowing, minimal-vegetation water are significantly larger than all other populations, which led to a main effect of flow. The interaction between vegetation and flow and the main effect of vegetation were not significant. Individual samples are represented by filled circles (●) for shoals in vegetated areas, and open circles (○) for shoals in nonvegetated or mixed habitats represent individual samples. Triangles group means are represented by filled triangles (▴) for shoals in vegetated areas, and open triangles (▵) for shoals in nonvegetated or mixed habitats. Error bars indicate one standard error. *P < 0.05. SV and SN were scored digitally and in real time, but data points from real-time observations are displayed. FV was scored in real-time. FM was scored in video and real time, and data from digital and real-time observations are presented. ANOVA, analysis of variance.