Figure 7

How grouping evolves. (A) Example of ancestor trace of attraction angle (a _A ) over evolutionary time. Blue: overall population distribution over attraction angle (a _A ); Black line: line of descent; Insets: turning groups, tPAIRS (top); straight moving groups, sPAIRS (bottom); Arrows indicate the relevant angle of attraction associated with these group movement patterns. (B) Per capita foraging efficiency of solitary (SOL), grouping individuals that only follow solitary individuals (sPAIR-S), and grouping individual that only group with each other (sPAIR-G). We measure average food items eaten per minute taken from 50 year samples of food intake from 30 SOL and sPAIR-S and 60 sPAIR-G individuals. Thus we compare 30 SOL-sPAIR-S pairs and 30 sPAIR-G-sPAIR-G pairs. sPAIRS-S represent the situation of a single grouping mutant when the first grouping mutant invades (e.g. year 250 in (A)). sPAIR-G represents the situation when multiple grouping individuals form groups. The latter case leads to an increase in foraging efficiency relative to sPAIRS-S revealing that mutual grouping generates a synergy. Box plots represent the median, upper and lower quartiles, and whiskers represent the full range of values. The solid horizontal line is the point at which energy intake due to feeding equals energy loss due to metabolism.