Chimpanzees exhibit exceptionally high levels of behavioral diversity compared to all other non-human species. This diversity has been documented in a variety of contexts, including the extraction of food resources, communication and thermoregulation. Many of these behaviors are assumed to be socially learned and group-specific, supporting the existence of chimpanzee cultures. As all other great apes, chimpanzees have come under enormous pressure by human activities, leading to a change of the natural environment. Their prime habitat, tropical rainforests and savanna woodlands, are increasingly converted to agricultural farmland, plantations and settlements, or otherwise degraded by the extraction of natural resources and infrastructure development.
Much of the empirical work and resulting debate on the loss of wildlife biodiversity has been conducted in the context of species decline or loss of genetic diversity and ecosystem functions. However, behavioral diversity is also a facet of biodiversity. Due to limited empirical data, until now it had been unclear whether behavioral diversity would similarly be negatively affected by human impact.
Data from 15 countries
An international research team, led by Hjalmar Kühl and Ammie Kalan of the Department of Primatology at the Max Planck Institute for Evolutionary Anthropology and the German Centre for Integrative Biodiversity Research (iDiv), compiled an unprecedented dataset on 31 chimpanzee behaviors across 144 social groups or communities, located throughout the entire geographic range of wild chimpanzees. Whereas part of this information was already available in the scientific literature, the international research team also conducted extensive field work at 46 locations, as part of the Pan African Programme, across 15 chimpanzee range countries over the last nine years. The particular set of behaviors considered in this study included the extraction and consumption of termites, ants, algae, nuts and honey; the use of tools for hunting or digging for tubers, and the use of stones, pools and caves among several others.
The occurrence of behaviors at a given site was investigated with respect to an aggregate measure of human impact. This measure integrates multiple levels of human impact, including human population density, roads, rivers and forest cover, all indicators for the level of disturbance and the degree of land cover change found in chimpanzee habitats. "The analysis revealed a strong and robust pattern: chimpanzees had reduced behavioral diversity at sites where human impact was high", explains Kalan, a researcher at the Max Planck Institute for Evolutionary Anthropology. "This pattern was consistent, independent of the grouping or categorization of behaviors. On average, chimpanzee behavioral diversity was reduced by 88 percent when human impact was highest compared to locations with the least human impact."
Potential mechanisms for loss of behaviors
As is known for humans, population size plays a major role in maintaining cultural traits and a similar mechanism may function in chimpanzees. Chimpanzees may also avoid conspicuous behaviors that inform hunters about their presence, such as nut cracking. Habitat degradation and resource depletion may also reduce opportunities for social learning and thus prevent the transfer of local traditions from one generation to the next. Lastly, climate change may also be important, as it may influence the production of important food resources and make their availability unpredictable. Very likely a combination of these potential mechanisms has caused the observed reduction in chimpanzee behavioral diversity.
"Our findings suggest that strategies for the conservation of biodiversity should be extended to include the protection of animal behavioral diversity as well", says Kühl, an ecologist at the iDiv research center and the Max Planck Institute for Evolutionary Anthropology. "Locations with exceptional sets of behaviors may be protected as 'Chimpanzee cultural heritage sites' and this concept can be extended to other species with high degree of cultural variability as well, including orangutans, capuchin monkeys or whales." These propositions are in accordance with existing biodiversity conservation efforts, such as the Convention on Biological Diversity or the Convention on the Conservation of Migratory Species of Wild Animals, of the United Nations Environment Programme, which calls for the protection of biological diversity in its entirety, including behavioral diversity of culturally rich wildlife.