Fight tactics in wood ants: individuals in smaller groups fight harder but die faster

Abstract

When social animals engage in inter-group contests, the outcome is determined by group sizes and individual masses, which together determine group resource-holding potential ('group RHP'). Individuals that perceive themselves as being in a group with high RHP may receive a motivational increase and increase their aggression levels. Alternatively, individuals in lower RHP groups may increase their aggression levels in an attempt to overcome the RHP deficit. We investigate how 'group RHP' influences agonistic tactics in red wood ants Formica rufa. Larger groups had higher total agonistic indices, but per capita agonistic indices were highest in the smallest groups, indicating that individuals in smaller groups fought harder. Agonistic indices were influenced by relative mean mass, focal group size, opponent group size and opponent group agonistic index. Focal group attrition rates decreased as focal group relative agonistic indices increased and there was a strong negative influence of relative mean mass. The highest focal attrition rates were received when opponent groups were numerically large and composed of large individuals. Thus, fight tactics in F. rufa seem to vary with both aspects of group RHP, group size and the individual attributes of group members, indicating that information on these are available to fighting ants.

Increased aggression during human group contests when competitive ability is more similar

“…RHP) based on photos of faces and bodies alone [11]. Like other animals (discussed in [7]), humans may furthermore engage in numerical assessment of their own and their opponent's group size, for instance, in warfare [12]. Thus, mutual assessment mechanisms may well be quite prevalent in our species.…”

“…Group RHP comprises both group size [7] and the individual characteristics of the group members [6]. In red wood ants (Formica rufa), for instance, larger groups are more likely to defeat smaller groups [7]. Similarly, in contests of groups of equal size, groups with individuals of higher fighting abilities (such as body mass and body size) have higher chances of winning the fight [6].…”

“…Outcomes may be determined by group RHP in such conflicts. Group RHP comprises both group size [7] and the individual characteristics of the group members [6]. In red wood ants (Formica rufa), for instance, larger groups are more likely to defeat smaller groups [7].…”

Bees at War: Interspecific Battles and Nest Usurpation in Stingless Bees

“…Fatal fighting is well documented in ants, where intraand interspecific battles between neighboring colonies can lead to enormous numbers of fatalities from both sides (Batchelor and Briffa 2011) and involve a wide rage of behaviors and outcomes, such as slave making (Hölldobler and Wilson 1990;Foitzik and Herbers 2001;Pohl and Foitzik 2011), raiding of nest provisions (Hölldobler and Lumsden 1980;Zee and Holway 2006;Hölldobler et al 2011), or fights on territorial boundaries or foraging trails (Hölldobler and Lumsden 1980;Hölldobler 1981;Adams 1994;Whitehouse and Jaffe 1996;van Wilgenburg et al 2005). In these eusocial insects, the fighting individuals are usually sterile workers, and their self-sacrificing behavior can be explained in evolutionary terms through the indirect fitness benefits of protecting the colony's reproducing adults (Hamilton 1964;Enquist and Leimar 1990;Boomsma and Franks 2006;Shorter and Rueppell 2012).…”

Infants use relative numerical group size to infer social dominance

“…To minimize the cost of fighting (e.g., energy spent and personal injury or death), natural selection appears to have favored the emergence of cognitive adaptations that help individuals predict whether they stand a chance against an opponent (2)(3)(4)(5). For example, many species, including ants, bees, birds, chimpanzees, and humans, appear to represent dominance relationships among conspecifics and use this information to decide whether to engage in or avoid a physical conflict (6)(7)(8)(9)(10). One such cue often associated with dominance ranking is physical size, with larger individuals often benefiting from greater strength and power over smaller individuals.…”