In territorial species, the distribution of neighbours and food abundance play a crucial role in space use patterns but less is known about how and when neighbours use shared areas in non-territorial species. We investigated space partitioning in 10 groups of wild, non-territorial mountain gorillas (Gorilla beringei beringei). Using location data, we examined factors influencing daily movement decisions and calculated the per cent overlap of annual kernel home ranges and core areas among neighbours. We found that the probability that a group chose an area was positively influenced by both food availability and the previous use of that area by the group. Additionally, groups reduced their overall utilization of areas previously used by neighbouring groups. Lastly, groups used their core areas more exclusively than their home ranges. In sum, our results show that both foraging needs and avoidance of competition with neighbours determined the gorillas' daily movement decisions, which presumably lead to largely mutually exclusive core areas. Our research suggests that non-territorial species actively avoid neighbours to maintain core area exclusivity. Together, these findings contribute to our understanding of the costs and benefits of non-territoriality.

Overall, despite the differences in food availability, we did not find large differences in the energetics of gorillas in the two populations, although further work is needed to more precisely quantify energy expenditure and energy balance. These results emphasize that even species with high food availability can exhibit behavioral and energetic responses to variable ecological conditions, which are likely to affect growth, reproduction, and survival.

The isotope ecology of great apes is a useful reference for palaeodietary reconstructions in fossil hominins. As extant apes live in C3-dominated habitats, variation in isotope signatures is assumed to be low compared to hominoids exploiting C4-plant resources. However, isotopic differences between sites and between and within individuals were poorly understood due to the lack of vegetation baseline data. In this comparative study we included all species of free-ranging African great apes (Pan troglodytes, Pan paniscus, Gorilla sp.).First, we explore differences in isotope baselines across different habitats and whether isotopic signatures in apes can be related to feeding niches (faunivory and folivory).Secondly, we illustrate how stable isotopic variations within African ape populations compare to other extant and extinct primates and discuss possible implications for dietary flexibility. Using 701 carbon and nitrogen isotope data points resulting from 148 sectioned hair samples and an additional collection of 189 fruit samples we compare six different great ape sites. We investigate the relationship between vegetation baselines and climatic variables, and subsequently correct great ape isotope data to a standardized plant baseline from the respective sites. We gained temporal isotopic profiles of individual animals by sectioning hair along its growth trajectory. Isotopic signatures of great apes differed between sites, mainly as vegetation isotope baselines were correlated with site-specific climatic conditions. We show that controlling for plant isotopic characteristics at a given site is essential for faunal data interpretation. While accounting for plant baseline effects, we found distinct isotopic profiles for each great ape population. Based on evidence from habituated groups and sympatric great ape species these differences could possibly be related to faunivory and folivory. Dietary flexibility in apes varied, but temporal variation was overall lower than in fossil hominins and extant baboons, shifting from C3 to C4-resources, providing new perspectives on comparisons between extinct and extant primates.

Space use patterns determine access to resources necessary for survival and reproduction. Although it is recognized that the interplay between social and ecological variables shapes spacing patterns, few studies in group-living animals have simultaneously assessed their importance in a comprehensive approach using different spatiotemporal space use measures. In territorial species, such patterns are strongly determined by between-group competition, but its impact in non-territorial species is poorly understood. To better understand the role of social and ecological variables in non-territorial mountain gorillas (Gorilla beringei beringei), we simultaneously evaluated the impact of between-group competition (local gorilla population density and frequency of intergroup encounters) and within-group competition (group size) on space use patterns in 13 gorilla groups in Bwindi Impenetrable National Park, Uganda, while also examining variation in food availability (herbaceous food availability and level of frugivory). We found evidence of between-group competition, indicated by a decline of both monthly home range size and frequency of revisits to each part of the home range as the local gorilla population density increased and by an increase in daily travel distance on days when intergroup encounters occurred. Within-group feeding competition was inferred by a decrease in the frequency of revisits as group size increased. Lastly, food availability influenced the gorillas' spacing patterns, as indicated by a decline in monthly home range size as herbaceous food availability increased and by an increase in daily travel distance as the degree of frugivory increased. In sum, our results suggest that Bwindi gorillas adapted their space use according to the constraints of intraspecific competition and the availability of food resources. We provide some of the first evidence of between-group competition influencing spacing patterns in a non-territorial species. This study suggests a gradient between territoriality and non-territoriality, along which the level of between-group competition varies.

One of the challenges facing conservationists is the conflict between humans and wildlife due to competition for resources. Ranging outside the national park and crop raiding by mountain gorillas Gorilla beringei beringei around Bwindi Impenetrable National Park, Uganda, is a major concern because it has negative impacts on both wildlife conservation and local livelihoods, particularly due to the high density of subsistence agriculturalists living along the park boundary. The objective of this study was to investigate the effects of food availability inside and outside the park on the occurrence of gorillas ranging outside the park and crop raiding. We collected data on 13 mountain gorilla groups ranging in three general locations on the edge of the park over a 13-month period. Using generalized linear mixed models, we found that the number of days both ranging outside the park and crop raiding was positively influenced by the availability of both tea Camellia sinensis and pine (Pinus sp.) plantations and uncultivated land, all of which contain herbaceous plants eaten by the gorillas, as well as due to the availability of palatable crops [bananas (Musa sp.), eucalyptus (Eucalyptus sp.) and sweet potatoes Ipomoea batatas]. Our results suggest that ranging outside the park and crop raiding were influenced by food availability outside the park, not by a lack of food resources inside the park. To stop gorillas from leaving the park, we recommend removing herbaceous foods consumed by gorillas from plantations and uncultivated land and planting of buffer crops. If kept clear of herbaceous foods and planted contiguously along the boundary, tea plantations may best serve as a buffer to prevent gorillas from using community land. This study shows that the mitigation of human-wildlife conflict requires research to inform appropriate management strategies based on the species' behavioral ecology.