A devastating hurricane transformed the monkey community by changing the pros and cons of interacting with others, new research shows.
Hurricane Maria hit Puerto Rico in 2017, killing more than 3,000 people. It also destroyed 63% of the vegetation on Cayo Santiago (also known as Monkey Island), which is home to a population of rhesus monkeys.
Even now, tree cover remains well below pre-hurricane levels, making shade a scarce and precious resource for the macaques in this hot part of the world.
The new study, led by the Universities of Pennsylvania and Exeter and published in the journal Scienceshows that the storm damage changed the evolutionary benefits of tolerating others and sharing shade – giving tolerant macaques a survival advantage.
Because many ecosystems are changing rapidly due to human activity, this study is an example of a species adapting its social strategy to survive.
“In response to the drastic changes caused by the hurricane, macaques have continuously increased tolerance and decreased aggression toward each other,” said Dr. Camille Testard of the University of Pennsylvania.
“This allowed more macaques to access the sparse shade, which is critical for survival.”
Dr. Testard added: “We examined ten years of data on the strength and number of social bonds of macaques, before and after the hurricane.
“Before the hurricane, tolerating others had no impact on the risk of death.
“Afterwards, macaques that showed greater than average social tolerance – and were therefore better able to share shade – were 42% less likely to die than those that were less tolerant.”
This represents a sudden change in ‘selection pressure’ – the evolutionary benefits or costs of different traits or behaviors.
Social behavior was assessed by recording aggression and how often individuals were seen together.
“Macaques are not the best at sharing resources – be it food or shade. They are known to live in an aggressive, highly competitive society,” says Professor Lauren Brent from the University of Exeter.
“But in the heat caused by ecological changes, often around 40 degrees Celsius, the macaques had to share space or die.”
Dr. Testard added: “To access shade, they must tolerate – and be tolerated by – others, and we found that this tolerance spills over into other daily interactions.
“Macaques that started sharing shade also spend time together in the morning, before the heat of the day forces them to seek shade.
“In fact, the hurricane changed the rules of the game in the monkey community.”
Professor Brent added: “For group-dwelling animals, social relationships can enable them to cope with environmental disturbances, including human-induced climate change.
“We were surprised that the macaques’ social behavior was so flexible, making them resilient to these environmental changes, but some species may not show the same flexibility.”
The research team consisted of Arizona State University and New York University.
Funders included the National Institutes of Health, the European Research Council, the National Science Foundation and the Royal Society.
The article is entitled: “Ecological disturbances alter the adaptive benefits of social bonds.”
