Annual temperatures are predicted to rise 3.6 degrees Fahrenheit (2 degrees Celsius) by mid-century in some climate models. Leaves that grow in hotter air contain more fiber and less digestible protein, meaning leaf-eaters would take longer to process their food.

In addition, the higher temperatures may force the animals to spend more time lounging in the shade to avoid overheating.

Such changes may force some gorilla and monkey species to sit still for long periods—time that would otherwise be used for finding food, protecting territory, or maintaining social bonds, the study says.

The inaction, combined with less nutritious food, could eventually cause mountain gorillas and African colobines—a large group of species including colobus monkeys—to go extinct, the study predicts.

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