Exploring ecological drivers of cultural variation and patterns of insectivory in the Nigeria-Cameroon chimpanzee (Pan troglodytes ellioti)

Tyler Andres-Bray

doi:10.17918/00010613

Chimpanzee insectivory is predominantly focused on social insects (e.g., termites and ants), as they have higher ratio of potential prey yield relative to predation effort. Chimpanzees invest considerable effort into cognitively complex, socially transmitted behaviors focused on acquiring social insects. Many of these behaviors include the modification and implementation of tools made from plant materials, though the methods for utilizing these tools and material preferences of these tools appear to vary culturally between chimpanzee communities, meaning that variation in the same type of tool use between communities is not explained by ecological differences. It has been suggested that insectivory and the complex behaviors used to acquire insect prey have contributed significantly to hominin evolution and encephalization, which implies social insects are a meaningful dietary resource for chimpanzees despite the relatively low proportion of their diets dedicated to insects (~5%). Given the potential importance of social insects as valuable diet items, the high degree of seasonally variability seen in chimpanzee insectivory is perplexing. Social insects are consumed in highly seasonal periods across many chimpanzee communities, and even among communities that consume social insects year-round there are pronounced seasonal peaks. This thesis explores patterns of variation in a common tool-use insectivorous behavior, termite fishing, as well as seasonal patterns of insect prey diversity in the unhabituated Ganga community of Nigeria-Cameroon chimpanzees (Pan troglodytes ellioti) in central Cameroon. To accomplish this, I used camera traps placed at 8 termite mounds near Ganga Research Station in Mbam & Djerem National Park from February 2020 to April 2023, a termite survey conducted at each of the 8 termite mounds from April 2022 to April 2023, and other biomonitoring data (fruit availability and fecal samples) collected at this site monthly from 2016 to 2023. I then combined quantitative ethnographic, quantitative ecological, and molecular methods to characterize behavioral and seasonal variation in the consumption of termites and other insect prey. I used these indirect methods of chimpanzee behavior and diet as the chimpanzees at Ganga are not habituated to human presence. Further, Ganga is an important community in which to study termite fishing, as the majority of studies on this behavior originate from chimpanzee communities inhabiting dense rainforest habitats, with a more recent push to characterize termite fishing in savanna chimpanzee communities as well. Ganga chimpanzees live in a complex savanna-forest ecotone in central Cameroon, and therefore may possess similarities with both rainforest and savanna chimpanzee communities. The first aim of this study was to identify termite fishing techniques and explore inter-individual variation in personal repertoires of P. t. ellioti at Ganga, and to situate patterns of termite fishing behavior at Ganga among that of other more well-studied chimpanzee communities. I identified 29 different termite fishing techniques in the Ganga community whose acquisition is consistent with trial-and-error development via social transmission. A combination of ecological similarity and geographic distance appear to contribute to cultural similarity in termite fishing between Ganga and other chimpanzee communities. The second aim of this study was to examine ecological correlates of termite fishing seasonality at Ganga. P. t. ellioti at Ganga have a highly seasonal period of termite fishing that occurs predominantly during the little rainy season from March to June. Seasonal exploitation of termites in this community appears mediated by termite accessibility in the upper portion of the soil surface. This accessibility appears to be related to termite reproductive behavior and is related to rainfall. Intermediate rainfall levels during the transition from the dry season to the little rainy season may cue termites to prepare for mating flights, which leads to greater presence in the soil surface and greater accessibility to predators. The third aim of this study employs molecular methods to explore seasonal consumption of social insects and insect prey diversity at Ganga using chimpanzee fecal samples. Results suggest infrequent, seasonal consumption of termites as well as frequent consumption of hymenopterans with seasonal peaks primarily in the dry season. Additionally, I found evidence of considerable indirect predation of other insect taxa whose lifecycles are strongly associated with plants or fruits that may be eaten by P. t. ellioti at Ganga. Finally, there was considerable inter-individual variation in arthropod prey between samples, but there is evidence of a more homogenous distribution of arthropod prey among samples from the dry season. The results of this thesis suggests a complex series of associations between environmental factors, insect consumption, and chimpanzee behavior. At Ganga, social insect consumption may be driven in part by opportunistic consumption of insects that are readily available, such as termites during the little rainy season. Environmental factors further appear associated with cultural elements of termite fishing tool use, given similarities in termite fishing between Ganga and distant communities with similar habitats. This suggests that chimpanzee habitats could contribute to chimpanzee cultural complexity. Finally, the high degree of potential secondary predation on a number of arthropod taxa points to an invisible source of nutrition available to chimpanzees, for which the degree of dietary contributions remains unknown. Altogether, insectivory at Ganga appears highly variable both between individuals and between seasons, which can ultimately have implications for nutrition and health in this community.

Exploring ecological drivers of cultural variation and patterns of insectivory in the Nigeria-Cameroon chimpanzee (Pan troglodytes ellioti)

Files and links (1)

Abstract

Metrics

Details

Exploring ecological drivers of cultural variation and patterns of insectivory in the Nigeria-Cameroon chimpanzee (Pan troglodytes ellioti)

Files and links (1)

Abstract

Metrics

Details

Drexel University Social media