Size distribution and battles in wood ants: group resource-holding potential is the sum of the individual parts

In battles between rival groups, aggression levels, and ultimately the outcome, may be influenced by the number of individuals and the resource-holding potential (RHP) of the individuals in each group. Since fighting in social animals can involve intragroup cooperation, the distribution of individual RHPs within the group could influence overall group ability. Thus, the total group fighting prowess might not simply equate to the sum of individual RHPs. We investigated the effects of within-group variance in individual RHP during battles in wood ants, Formica rufa. Rival groups were matched in number of individuals and mean body size of individuals but differed in the variance among body sizes. Larger individuals were most aggressive and small individuals were least aggressive. Overall, small individuals had the highest attrition rate and large individuals the lowest, with medium-sized individuals experiencing moderate attrition rates. Consequently, aggression and attrition rates in low-variance groups did not differ significantly from rates in high-variance groups, indicating that when group size and mean body mass are equal, the distribution of individual RHPs does not influence the overall fighting ability of the group. Rather, it appears that large individuals are able to compensate for poor performance by weaker group members.