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Gregariousness, foraging effort, and social interactions in lactating bonobos and chimpanzees

Citation

Lee, Sean et al. (2020), Gregariousness, foraging effort, and social interactions in lactating bonobos and chimpanzees, Dryad, Dataset, https://doi.org/10.5061/dryad.d51c5b01v

Abstract

Fission-fusion dynamics have evolved in a broad range of animal taxa and are thought to allow individuals to mitigate feeding competition. While this is the principal benefit of fission-fusion, few studies have evaluated its costs. We compared gregariousness, foraging budgets, and social budgets between lactating bonobos and chimpanzees from wild populations to evaluate such costs. Both species exhibit fission-fusion dynamics, but chimpanzees, particularly in East African populations, appear to experience higher feeding competition than bonobos. We expected lactating chimpanzees to be less gregarious than lactating bonobos; reduced gregariousness should allow lactating chimpanzees to mitigate costs of higher feeding competition without requiring more foraging effort. However, we expected the reduced gregariousness of lactating chimpanzees to limit their time available for affiliative social interactions. Using long-term data from LuiKotale bonobos and Gombe chimpanzees, we found that lactating chimpanzees were indeed less gregarious than lactating bonobos while feeding and travel time did not differ between species. Contrary to our predictions, lactating females did not differ in social interaction time, and lactating chimpanzees spent proportionately more time interacting with individuals other than their immature offspring. Our results indicate that lactating chimpanzees can maintain social budgets comparable to lactating bonobos despite reduced gregariousness and without incurring additional foraging costs. We discuss potential explanations for why lactating bonobos are more gregarious.

Funding

Max-Planck-Gesellschaft

Federal Ministry of Education and Research

Royal Zoological Society of Antwerp

Bonobo Alive

Jane Goodall Institute

National Institutes of Health, Award: R00HD057992

Leo S. Guthman Foundation

National Geographic Society

George Washington University

Explorers Club Washington Group

Sigma Xi

Leakey Foundation

Wenner-Gren Foundation

Federal Ministry of Education and Research

Royal Zoological Society of Antwerp

Bonobo Alive

Leo S. Guthman Foundation

Explorers Club Washington Group