It looks like humans aren’t the only assholes in nature.
According to a recent study published in eLife, Long-tailed macaques on islands off the coast of Thailand have become proficient with stone tools, and are now using them to break open shellfish. Except their technological progression is now threatening to wipe out the islands’ shellfish altogether.
This impact on the environment is what is known as ecosystem engineering, or niche construction. These monkeys, similar to humans, are able to affect their ecosystem to a great degree with their behaviour.
The macaques target the largest rock oysters, and bash them with stone hammers, then pry open the shells covering the most nutritious snail and crab meat using the flattened edges of their tools.
These macaques are one of several primates known to use stone tools, such as chimpanzees in Africa, bearded capuchins in South America, and orang-utans in Asia. “Stone tools open up an opportunity for foods they otherwise wouldn’t even be able to harvest,” says Lydia Luncz at the University of Oxford.
The two islands, both alike in shellfish populations, differed only in the number of macaques there. Koram has around 80 primates, while NomSao has only 9. Both groups figured out how to use rocks to break open shellfish armour — behaviour that has been seen in other groups of macaques in Thailand.
On Koram, though, the large number of of tool-wielding macaques has led to a crisis. The researchers estimate that a single macaque on the island consumes 47 shellfish a day, mostly oysters. For the mere 26 macaques that the researchers studied, that works out to 441,000 a year.
Looking at periwinkles — a small sea snail — the researchers estimated that the monkeys could eat the entire island’s population in just a year. On NomSao, the smaller group of 9 eats only about an eighth of the available periwinkle population.
It’s hard not to see the Koram as a microcosm of our own planet right now. Even though fresh supplies of shellfish wash up on the island, the monkeys are still consuming them at an unsustainable rate.