Groups of animals consider multiple factors before deciding whether to fight rivals, according to new research involving the University of Plymouth.

Before one-on-one fights, animals are known to make decisions based on factors including the size and strength of the opponent, the outcome of recent fights and the importance of the prize.

But scientists from the universities of Plymouth and Exeter say previous research has often overlooked complexity in group conflicts and assumed that larger groups will always win.

Instead, they say factors like group cohesion and teamwork, the strength of individual members and the location of battle all likely play a part – and animal groups weigh up the situation before fighting.

The research, published in the journal Trends in Ecology and Evolution, was funded by the Human Frontiers Science Program and the Natural Environment Research Council.

Dr Mark Briffa

Co-author Mark Briffa, Professor of Animal Behaviour at the University of Plymouth, said:

“Researchers have spent years wondering about the extent to which individual fighting animals use ‘assessment’ – effectively, sizing their opponent up. In this paper, we explore the scope for groups of rivals to do a similar thing.
"This could be a possibility in many examples across the animal kingdom where individuals work collectively, such as battles between rival groups of ants or even warfare between rival groups in humans.”

Fights between social groups are common in nature and groups with more members are often assumed to be the likely winners of any fight.

Previous studies of animals including primates, lions, birds and ants show this is often correct, however, the current research highlights other factors that can play a part:

  • Strong individuals: Among grey wolves, smaller groups with more males – which are bigger and stronger than females – can overcome larger groups;
  • Motivation: Meerkat groups that contain pups can win despite inferior numbers – suggesting a "motivation advantage" because gaining new territory can result in more food for their young;
  • Chances of winning: Studies of turtle ants, which have multiple nests, suggest they prioritise defending those with narrower entrances – as larger entrances are harder to defend. This allows them to successfully defend certain parts of their territory;
  • Winner/loser effect": Losers of baboon intergroup conflicts spend less time in the area where the fight occurred than they did before the fight, suggesting they avoid areas where they previously lost;
  • Social cohesion: In months in which they have lots of intergroup fights, chimpanzee social groups are more cohesive and males are less aggressive within the group, suggesting cohesion may be useful at times when fights are likely.
Lead author Dr Patrick Green, of the Centre for Ecology and Conservation at the University of Exeter, said:

"Any potential fight – whether between humans or animals – gets more complex if there are multiple individuals on each side. Groups may assess both the importance of whatever they're fighting about, and a range of factors about their own group and the opponent.
“Research on dyadic (one-on-one) fights has developed an advanced framework on 'assessment' – how animals gather information and decide whether to fight, how much effort to put in, and if and when to give up. However, studies on group contests among social-living animals haven’t generally focused on assessment. Understanding more about this can teach us not only about evolution, but also about conflict in humans."

The full study – Green et al: Assessments during Intergroup Contests – is published in Trends in Ecology and Evolution, doi: 10.1016/j.tree.2020.09.007.

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