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iDEA: DREXEL LIBRARIES E-REPOSITORY AND ARCHIVES

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Linking behavioral diversity with genetic and ecological variation in the Nigeria-Cameroon (Pan troglodytes ellioti)

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Title
Linking behavioral diversity with genetic and ecological variation in the Nigeria-Cameroon (Pan troglodytes ellioti)
Author(s)
Abwe, Ekwoge Enang
Advisor(s)
Gonder, Mary
Keywords
Biology; Chimpanzees; Rain forests; Ecotones; Habitat (Ecology)
Date
2018-03
Publisher
Drexel University
Thesis
Ph.D., Biological Sciences -- Drexel University, 2018
Abstract
Tropical rainforests are rich in vertebrates, the result of processes that generate and maintain biological diversity, and low extinction rates under relatively stable climatic conditions. The Gulf of Guinea in Central/West Africa is a biodiversity hotspot with several endemic species, including several primate species. The diversity of endemic species found in this region has been attributed to a complex forest history during the Pleistocene; habitat variation associated with the confluence of the Gulf of Guinea rainforest to the west with the Congo Basin rainforest to the south and drier savanna habitats to the north; and biogeographic barriers including the Cameroon Highlands and riverine barriers, such as the Sanaga River in Central Cameroon. The contributions of the Sanaga River and Cameroon Highlands in promoting species diversification have been examined in some detail, and a growing body of data, suggests that environmental variation, particularly in an ecotone area in southern Cameroon has been important in promoting the diversification of birds, lizards and insects. Little is known about whether ecological variation has contributed to the diversification of endemic mammals across this region. The chimpanzees of Cameroon present a unique opportunity to investigate how ecological variation contributes to promoting intraspecific divergence in the endemic mammals of the region. In addition to harboring two chimpanzee subspecies (Pan troglodytes troglodytes and P. t. ellioti), there are two distinct gene pools associated with P. t. ellioti. These two gene pools were previously shown to inhabit two significantly different niches - one associated with the mountainous rainforest habitats found in western Cameroon and one associated with the ecotone habitats found in central Cameroon. This thesis explores environmental and ecological differences between rainforest and ecotone habitats at a fine geographic scale, and compares and contrasts chimpanzee socioecology patterns between these habitats. Research was conducted from January 2016 to December 2017 at three study sites to represent a range of environments inhabited by P. t. ellioti. I completed surveys for 15 months (January 2016 to March 2017) at two rainforest sites (Njuma and Bekob) in Ebo forest. Njuma was selected for study because it represents relatively undisturbed lowland rainforest, whereas Bekob represents a regenerating human-modified lowland rainforest landscape. Complementary studies were also completed for 24 months (January 2016 to December 2017) at one ecotone site in Mbam & Djerem National Park (Ganga). Quantitative ecological methods were used to characterize habitats and the seasonal availability of fleshy fruits that are important to chimpanzees. Since chimpanzees across the sites are not habituated to humans, I used indirect methods (fecal samples and nests) to investigate chimpanzee diet and nesting patterns. The first aim of study was to examine whether and how the niches of P. t. ellioti in western Cameroon (Njuma and Bekob) differed from the niche occupied by P. t. ellioti in central Cameroon (Ganga) at fine geographic scale. The main variables that distinguished the rainforest from the ecotone habitats included rainfall (annual amounts are higher at the rainforest) and the diversity, density and size of trees (higher at the rainforest than the ecotone). On the other hand, the ecotone had a higher density of lianas and terrestrial herbaceous vegetation. The availability of fleshy fruits was higher at the ecotone, though with marked seasonality compared to the rainforest. At Bekob, there was the prevalence of introduced and secondary forest plant species that I predicted to be important in the socioecology of chimpanzees. The second aim of the study was to examine how occupying rainforest and ecotone niches impact chimpanzee feeding behavior. The main differences in the dietary ecology of the ecotone and rainforest chimpanzees were in the seasonal variation of fleshy fruits and fibrous foods in their diets. Fleshy fruits were the most important dietary component for rainforest chimpanzees in the dry season, whereas the diet of the ecotone chimpanzees was dominated by fibrous foods. Conversely, in the wet season, the proportion of fleshy fruits was more significant in the diet of the ecotone chimpanzees, while fibrous foods were of more significance for the rainforest chimpanzees. Consistent with other human-modified environments, introduced and secondary forest species including Elaeis guineensis and Musanga cecropioides were important dietary components for chimpanzees at Bekob, especially during periods of low fleshy fruit availability. Animal consumption, including vertebrates and invertebrates was more significant at Ganga, and was inversely associated with fleshy fruit consumption. Finally, the third aim of the study was to examine how occupying rainforest and ecotone niches impact chimpanzee nesting behavior. Fruit phenology was an important factor in nesting site selection at the ecotone while rainforest chimpanzees selected steep slopes, hypothesized as an antipredation strategy. Larger nest groups sizes were linked to periods of higher fruit availability especially at the Ganga. Chimpanzees across the three sites had site specific preferences for nesting tree species, but Strombosia grandifolia was commonly preferred across the sites, while nesting in Elaeis guineensis was exclusive to chimpanzees at Bekob. The dietary and nesting patterns of chimpanzees differed considerably between rainforest and ecotone, and may have implications that will improve understanding about why this region is an important area for the genetic diversification of chimpanzees. The ecotone habitat of Ganga is characterized by marked seasonality in fleshy fruit availability and seasonal dietary shifts at the ecotone could imply wider ranging, larger territories and lower levels of gregariousness among chimpanzees. In contrast, the rainforest habitats of Njuma and Bekob are characterized by less pronounced seasonality in fleshy fruits and seasonal dietary shifts. This could reflect smaller territories and more sociality in the rainforest chimpanzee populations. This differentiation in socioecological patterns may be responsible for observed genetic patterns in chimpanzees across this region.
URI
http://hdl.handle.net/1860/idea:7885
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