Tough life in the savannah? Chimpanzee foods are mechanically more demanding than previously thought

Date:  August 10, 2018

Source:  Max Planck Institute for Evolutionary Anthropology

Summary:

A study has analyzed the mechanical properties and the isotopic composition of plant foods eaten by chimpanzees living in the tropical rain forest and savannah woodland. They found that the savannah chimpanzees eat foods that are more mechanically challenging and therefore may place higher selective pressures on their chewing apparatus compared to their conspecifics living in the rainforest.

Chimpanzees are generally known as the ripe fruit specialist among the great apes but also incorporate other food items such as leaves and seedpods into their diets. Savannah chimpanzees are thought to rely on these non-fruit resources more than their forest counterparts. The mechanical properties of plant foods can vary substantially but to date there were no comparative data available for chimpanzee populations living in distinct habitat types.

Adam van Casteren of the Max Planck Weizmann Center for Integrative Archaeology and Anthropology at the Max Planck Institute for Evolutionary Anthropology went out to compare the material properties of various plant foods eaten by chimpanzees in a tropical rainforest (Ngogo, Uganda) and a savannah woodland (Issa Valley, Tanzania). Using a portable mechanical tester, he measured the physical properties of plant tissues and found that some plant parts from the mosaic savannah woodland habitat, such as the outer casing of the Strychnos fruit, had much higher toughness and stiffness values than the plant tissues he tested from the rainforest. "I was surprised to see that some values even exceed those recorded for orangutan foods as they are generally considered to consume the most mechanically challenging diet of all the great apes," says van Casteren.

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