The 85th Annual Meeting of the American Association of Physical Anthropologists (2016)

Low Mortality Rates among Ngogo Chimpanzees: Ecological Influences and Evolutionary Implications


1Anthropology, Yale University, 2Anthropology, University of Michigan, 3School of Human Evolution and Social Change, Arizona State University

April 16, 2016 18, Atrium Ballroom A/B Add to calendar

Data on chimpanzee (Pan troglodytes) life histories and demography are invaluable for investigating human life history evolution and reconstructing life history parameters in extinct hominins. We add to the chimpanzee comparative sample with the first formal analysis of mortality rates in the unusually large Ngogo chimpanzee community. We also provide a novel method for estimating survivorship under the assumption that age estimations for chimpanzees are imperfect and increasingly error prone for older individuals. We used life table and survivorship analyses of yearly field records to characterize mortality during 1995-2014. We find that the Ngogo chimpanzee community experienced the lowest mortality of any community studied thus far, which partially explains why it is so large. Notably, mortality was significantly lower than at Kanyawara, in the same park only 10 km away. Ecological factors presumably reducing mortality at Ngogo relative to Kanyawara include: historical absence of commercial logging; higher fruit abundance; higher energy intake rates; and less extensive food shortages. Lack of serious epidemics, better habitat protection, and the absence of large felids at Ngogo may also contribute to lower mortality than at other sites. However, the absence of predators cannot explain the Ngogo-Kanyawara contrast. Ngogo mortality rates are similar to or lower than human hunter-gatherer populations until age 45, after which mortality notably increases. Thus even under Ngogo’s advantaged ecological conditions, differences between chimpanzee and human mortality rates persist. The data presented here provide insights into derived features of human life history and factors that influence human life history evolution.

L.S.B. Leakey Foundation, National Geographic Society, US National Science Foundation and IOB-0516644, Yale University, University of Michigan, Boston University, MPI for Evolutionary Anthropology, Arizona State University