A review of great ape behavioural responses and their outcomes to anthropogenic landscapes.

Industrial expansion has brought humans and wildlife into closer contact, and added novel, complex dimensions to human-wildlife relationships. The seven great apes (chimpanzee, Bornean orangutan, Sumatran orangutan, Tapanuli orangutan, Eastern gorilla, Western gorilla, bonobo), the closest extant relatives to humans, have experienced substantial population declines resulting from anthropogenic activities. The effect of human activity on great ape behavioural ecology is therefore an emerging field of inquiry in primatology which has historically been minimally considered. This review explores how wild great apes respond behaviourally to human activities and environmental changes, synthesizing current knowledge and addressing potential outcomes and risks. Using precise search criteria, we found 96 studies documenting changes in great ape behaviour in response to human activity, and despite their broad geographic distribution, we found common patterns and responses across species to increasing human influence. Literature documented shifts in existing behaviour (57), the generation of novel behaviours (53) or reported both (15). Forty-three studies (45%) included direct (23) or indirect (20) assessment of the consequences of these behaviours. Only one study modelled a widespread loss of existing behaviours. The majority of studies included chimpanzees (67), followed by orangutans (19) and gorillas (19), and only 2 included bonobos. We found that the most frequently documented drivers of behavioural responses to anthropogenic activity were wide-scale land-use conversions in ape habitats. In response, apes have adopted crop foraging, and altered nesting behaviour, range use, and social strategies. While these responses appear to allow survival in the immediate sense, they may expose individuals to more risks in the long term. Analysis revealed that under many contexts changing great ape behaviour is putting strain on the human-ape relationship, resulting in injury, harassment, and even the killing of apes. We found examples of tolerant relationships between humans and apes shifting towards conflict, potentially worsening the conservation crisis and inviting inquiry into tolerance thresholds among human communities. We emphasize the importance of community-engaged strategies for reducing competition over resources and conclude that great ape behavioural responses to human activity must be interpreted through a locally specific lens.