Landscapes of the apes: modelling landscape use of chimpanzees and early hominins across an environmental gradient.

Abstract

As primate habitat is declining rapidly, studying the flexibility of primates to adapt to changing landscapes is important. Landscape-scale studies of primate habitat use are, however, scant. Predictive models can provide important tools in investigating primate landscape use. Chimpanzees (Pan troglodytes) face habitat loss throughout their range, but their susceptibility to change remains unclear. Changing landscapes also played a vital role in human evolution, but evidence on early hominin behaviour remains limited. Chimpanzee responses to changing landscapes may provide new insights into early hominin landscape use due to chimpanzees’ close relatedness to humans. This thesis used individual-based and referential modelling to explore hominid (i.e. chimpanzee, Ardipithecus ramidus and Australopithecus anamensis/ afarensis) landscape use along an environmental gradient from forests to savannahs to determine their adaptability to change. Based on literature review, this thesis first quantitatively defined chimpanzee landscapes as dense forests, forest mosaics and savannahs using vegetation and climate data. Relationships between chimpanzee behaviour and habitat were identified based on literature and expert reviews. Data were used to set out rules for a NetLogo individual- based model on chimpanzee landscape use. Model output highlighted differences in activity budgets, internal states and daily path lengths for chimpanzees in forests, mosaics and savannahs due to the availability of resources. Maintaining homeostasis was increasingly more difficult in more open landscapes. A savannah chimpanzee case study model based on field data for Issa, Tanzania, verified these findings and showed that savannah chimpanzees faced particular survival challenges; additional adaptations were necessary for survival. Using a referential modelling approach and adapting the chimpanzee models to suit early hominin diet and morphology, early hominin landscape use models highlighted that, similar to chimpanzees, early hominins struggled more in savannahs than in forests. Early hominins were, however, more successful in maintaining homeostasis and more optimally used open vegetation as compared to chimpanzees, due to their morphological adaptations to a wider dietary breadth and bipedality, providing greater locomotor efficiency and better thermoregulatory abilities. Australopithecus was more successful than Ardipithecus. This research thus quantitatively characterised the selective pressures that shape hominid landscape use, and thereby provided a unique contribution to primatology and human origin studies. Models have important applications for conservation and further research, such as exploring the environmental context of hominid evolution and predicting the impacts of various landscape changes on hominid survival.