Unaffected Survivorship as a Result of Early Life Ecological Stress in Wild Chimpanzees (Pan troglodytes schweinfurthii) at Gombe National Park, Tanzania
Open AccessThis thesis aims to characterize annual food availability at Gombe National Park, Tanzania and analyze wild chimpanzee (Pan troglodytes) survival responses to decreased fruit availability. After compiling and analyzing 40 years of behavioral data, average annual diet proportions for the four major chimpanzee food types (fruit, leaves and pith, fauna, and other) were created for each year in the study period, 1975-2015. These averages were then used to identify years in which fruit consumption, a chimpanzee preferred food item, was greater than one standard deviation below the mean. Demographic data from the study site was used to identify population individuals born during these years designated as “nutrient scarce” and their lifespans up until 10/11/2020 were calculated. Kaplan-Meier survival curves were generated to visualize chimpanzee survival of individuals born during scarce years and compare their survival with individuals born during average years. After constructing four Cox proportional hazards models to examine chimpanzee survival until four critical development periods, age one, age five, age 10, and survival overall, no difference in survival was found between the individuals born during nutrient scarce years and those born during average years at any age. Maternal rank was included in the model as a second predictor variable and was found to have no impact on survival when also exposed to low fruit availability. Maternal rank and nutrient scarcity had no significant interaction in the model. We can assume due to the small sample size of individuals born during nutrient scarce years and the relative abundance of fall-back foods within the park, individuals born during these periods are buffered from any long-term impacts of nutritional early life adversity.
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