“From individual to group territoriality: Competitive environments promote the evolution of sociality”

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Markus Port, Oliver Schülke, and Julia Ostner

Competition promotes the evolution of sociality

Male Verreaux’s sifaka can defend exclusive access to a group of females or share their territory with other males. This type of social organization appears to be a transient state between individual and group territoriality.
(Credit: Manfred Eberle)

Most of us might think that competition generates aggression. A study appearing in The American Naturalist shows, however, that this need not be the case – at least not in territorial animals, where competition can actually pave the way for the evolution of sociality.

Male Verreaux’s sifaka can engage in fierce fights over territories, but they can also be fairly tolerant towards each other. As a result, some males defend exclusive access to small groups of females, whereas others share their territories with other males, and drive off competitors together. “At first glance, it looks like these lemurs are caught in an evolutionary transition between individual territoriality and sociality,” says Markus Port, first author of the study, “but our analyses show that social systems like the one of Verreaux’s sifaka can actually be a stable endpoint of evolution.”

Port and his colleagues Oliver Schülke and Julia Ostner from Göttingen University in Germany have developed a game-theoretic model, in which they show that these ‘mixed equilibria’ can be the result of a coevolutionary feedback between the behavior of territory owners and outsiders, where owners adjust their degree of tolerance to the level of aggression imposed on them by outsiders and vice versa. Perhaps surprisingly, their analyses also show that elevated competition leads to more tolerance and lower levels of aggression.

“The reason is that strong competition puts owners in strong demand for helpers to help them defend their territories,” explains Port, “such that tolerant owners and peaceful outsiders outperform mutually aggressive conspecifics.” Strong competition, therefore, does not necessarily select for elevated territorial aggression, but can rather drive the evolution of sociality. Read the Article