Spider monkeys crowdsource best places to eat in forest
Spider monkeys don’t forage at random, but instead pool knowledge about where to find the best fruit in the forest, according to new research.
A study based on seven years of field observations in Mexico’s Yucatán Peninsula shows that spider monkeys, known for their long limbs and tails, have developed a kind of natural crowdsourcing system for finding food.
The scientists behind the study, from Heriot-Watt, the University of Edinburgh and the National Autonomous University of Mexico, wanted to use the field data to help explain a feature of spider monkey social behaviour: group members split into small subgroups, then rejoin in different combinations The same subgroup might never forage together twice.
Importantly, we found that these patterns aren’t explained by factors like age, sex or immigration status, which suggests they’re linked to how the monkeys gather and exchange information rather than who they are.
The findings are published in the journal npj Complexity.
Dr Matthew Silk, an ecologist from the University of Edinburgh, said: “It isn’t random social mingling; it's a clever system for sharing insider knowledge about where the best fruit trees are located across their forest home.
“By constantly changing their subgroups, monkeys who know different parts of the forest can share information about where fruit is available.
“We tracked individual monkeys’ movements and mapped out their core ranges, or the areas each monkey knows well.
“Some parts of the forest are known by multiple monkeys, like a town’s most popular restaurant, while others are known by only one or two monkeys, like a hidden gem.”
“There's enough overlap for monkeys to meet and exchange tips, but enough separation that each monkey scouts different parts of the forest. This maximises the whole group's collective coverage of the best feeding spots.”
Complex mathematics mapped the monkeys
Traditional ecological models can only analyse pair relationships, how one monkey meets another, but spider monkeys often travel in subgroups of three or more and their ranges also overlap in sets of three or more.
Ross Walker, a PhD student in Heriot-Watt's School of Mathematical and Computer Sciences, developed a new method based on abstract mathematical theory rather than rainforest ecology.
Ross said: “As you can imagine, if you’re trying to map how subgroups of monkeys move, when those subgroups change several times a day, any graph can start to look very messy.
“I developed a new approach based on simplicial complexes, which allowed me to capture how whole subgroups interact.
“This approach helped identify where monkeys’ knowledge about the forest overlaps, and where there are gaps.
“Those gaps matter, because they suggest that some subsets of individuals know things about parts of the environment that others don’t.
“The fact that these subgroups regularly meet and mix means that information can potentially be shared across the whole group.
“Importantly, we found that these patterns aren’t explained by factors like age, sex or immigration status, which suggests they’re linked to how the monkeys gather and exchange information rather than who they are.”
Optimal middle ground between sticking together and spreading out
Ross continued “We’ve shown that there’s an optimal middle ground between the monkeys sticking together and spreading out too far.
“It’s not helpful if every monkey knows exactly the same thing, and it’s not helpful if no one ever meets.
“It’s best when individuals explore different areas, but still reconnect often enough to pool what they’ve learned.”
Professor Gabriel Ramos-Fernandez, from the National Autonomous University of Mexico, said: “We have shown that the fluid social dynamics of spider monkeys has an important consequence for their foraging success: by exploring their environment in a distributed fashion and then coming together to share their uniquely obtained information, the group as a whole can know the forest better than a single individual could on its own.
“This foraging strategy is a good example of collective intelligence in natural conditions.
“In further work, we would like to use the same mathematical techniques to explore other interactions between more than two individuals, which are very common and understudied.
“For example, they could serve for studying many aspects of social dynamics in this and other species that form temporary subgroups.
“Also, we would like to test the efficiency of this type of distributed foraging strategy in other species and environments with different degrees of temporal and spatial variability.”
Watch the video explainer, produced by the Global Research Centre for Diverse Intelligences at the University of St Andrews, where Gabriel is a global partner.
