An Original Theoretical Framework for Adaptive Behaviour and Decision-Making Under Predation Risk in African Forest Primates: Evidence from Cross River Gorilla and Chimpanzee

This dissertation develops an original theoretical framework for adaptive behavioural decision-making under predation risk in African forest primates, using the critically endangered Cross River gorilla Gorilla gorilla diehli and Nigeria-Cameroon chimpanzee Pan troglodytes ellioti in Cross River State, South South Nigeria as dual study systems. The dissertation addresses a gap in primate behavioural ecology by developing and testing a novel multi-threat risk allocation model that predicts how primates balance predation avoidance against foraging opportunity, intra-group competition, and reproductive investment under varying threat configurations. Behavioural data were collected using continuous focal animal sampling over 36 months on habituated gorilla and chimpanzee communities in Afi Mountain Wildlife Sanctuary and adjacent forest. A total of 2,800 focal hours were accumulated. Threat levels were quantified by ranger encounter rates, hunter-sign surveys, and habitat disturbance indices. Vigilance behaviour, group cohesion, habitat use selection, and travel paths were the primary response variables. An original Integrated Threat Response Model (ITRM) is developed and tested using information-theoretic model selection. Results demonstrate that gorillas show risk-sensitive habitat avoidance consistent with ITRM predictions while chimpanzees show a more flexible adjustive strategy consistent with sequential threat assessment. Group size was a stronger modulator of individual vigilance allocation in chimpanzees than gorillas. These findings contribute original insights into the cognitive and social factors mediating predation risk response in critically endangered great apes and provide behavioural benchmarks for ITRM application to managed population contexts. Keywords: predation risk, primate behaviour, Cross River gorilla, chimpanzee, adaptive decision-making.