Hunting of mammals by central chimpanzees (Pan troglodytes troglodytes) in the Loango National Park, Gabon

The locomotor ecology of wild western lowland gorillas: How does the largest ape exploit complex arboreal environments?

Western lowland gorillas are the largest and most sexually dimorphic ape that habitually exploits arboreal environments. Their size, robust musculature and specialised adaptations in the hands and feet, which are suited for terrestrial quadrupedal locomotion, make them interesting models for understanding how great apes are able to exploit complex arboreal habitats. We present a comprehensive analysis of the arboreal locomotor ecology of western lowland gorillas by studying their behaviour and ecology in the context of their morphology. A group of fully habituated wild western lowland gorillas was followed for 12 months in Loango National Park, Gabon. Statistical analysis applying regression modelling and Akaike's Information Criterion was used to identify the relationships between locomotor behaviours, height, contextual behaviour, support use, hand posture and body size. Our findings suggest that the gorillas were not restricted in their ability to access and move around in tree canopies because of their size or postcranial morphology. Instead, they exhibited considerable behavioural flexibility and engaged in locomotor behaviours that contradicted classic body size predictions for primates. To offset the risks of moving on small supports, the gorillas used hand-assisted bipedal locomotion on multiple small supports, rather than relying on suspensory locomotion. We suggest that this is linked to their hand dimensions, which have been selected to facilitate efficient quadrupedal walking on the ground. The silverback gorilla engaged in less horizontal locomotion in the canopy, spent less time at heights above 20 m, and used large supports more often than the adult females, blackback and adolescents, but the type and number of supports used did not vary between body size groups. We also found that the reproductive status of the females (presence or absence of small infants) may have shaped how they responded to risks when solving the problem of gap-crossing in the trees. Overall, our results highlight that the gorillas likely prioritised risk minimisation in the supports that they used in arboreal environments at the cost of increased energy expenditure.

Evaluating the efficacy of a consumer-centric method for ecological sampling: Using bonobo (Pan paniscus) feeding patterns as an instrument for tropical forest characterization

Characteristics of food availability and distribution are key components of a species' ecology. Objective ecological surveying used in animal behavior research does not consider aspects of selection by the consumer and therefore may produce imprecise measures of availability. We propose a method to integrate ecological sampling of an animal's environment into existing behavioral data collection systems by using the consumer as the surveyor. Here, we evaluate the consumer-centric method (CCM) of assessing resource availability for its ability to measure food resource abundance, distribution, and dispersion. This method catalogs feeding locations observed during behavioral observation and uses aggregated data to characterize these ecological metrics. We evaluated the CCM relative to traditional vegetation plot surveying using accumulated feeding locations across 3 years visited by a tropical frugivore, the bonobo (Pan paniscus), and compared it with data derived from over 200 vegetation plots across their 50 km2+ home ranges. We demonstrate that food species abundance estimates derived from the CCM are comparable to those derived from traditional vegetation plot sampling in less than 2 years of data collection, and agreement improved when accounting for aspects of consumer selectivity in objective vegetation plot sampling (e.g., tree size minima). Density correlated between CCM and plot-derived estimates and was relatively insensitive to home range inclusion and other species characteristics, however, it was sensitive to sampling frequency. Agreement between the methods in relative distribution of resources performed better across species than expected by chance, although measures of dispersion correlated poorly. Once tested in other systems, the CCM may provide a robust measure of food availability for use in relative food availability indices and can be incorporated into existing observational data collection. The CCM has an advantage over traditional sampling methods as it incorporates sampling biases relevant to the consumer, thereby serving as a promising method for animal behavioral research.

Extending neural systems for navigation to hunting behavior

For decades, a central question in neuroscience has been: How does the brain support navigation? Recent research on navigation has explored how brain regions support the capacity to adapt to changes in the environment and track the distance and direction to goal locations. Here, we provide a brief review of this literature and speculate how these neural systems may be involved in another, parallel behavior-hunting. Hunting shares many of the same challenges as navigation. Like navigation, hunting requires the hunter to orient towards a goal while minimizing their distance from it while traveling. Likewise, hunting may require the accommodation of detours to locate prey or the exploitation of shortcuts for a quicker capture. Recent research suggests that neurons in the periaqueductal gray, hypothalamus, and dorsal anterior cingulate play key roles in such hunting behavior. In this review, we speculate on how these regions may operate functionally with other key brain regions involved in navigation, such as the hippocampus, to support hunting. Additionally, we posit that hunting in a group presents an additional set of challenges, where success relies on multicentric tracking and prediction of prey position as well as the position of co-hunters.

Lethal coalitionary attacks of chimpanzees (Pan troglodytes troglodytes) on gorillas (Gorilla gorilla gorilla) in the wild

Intraspecies violence, including lethal interactions, is a relatively common phenomenon in mammals. Contrarily, interspecies violence has mainly been investigated in the context of predation and received most research attention in carnivores. Here, we provide the first information of two lethal coalitionary attacks of chimpanzees (Pan troglodytes troglodytes) on another hominid species, western lowland gorillas (Gorilla gorilla gorilla), that occur sympatrically in the Loango National Park in Gabon. In both events, the chimpanzees significantly outnumbered the gorillas and victims were infant gorillas. We discuss these observations in light of the two most widely accepted theoretical explanations for interspecific lethal violence, predation and competition, and combinations of the two-intraguild predation and interspecific killing. Given these events meet conditions proposed to trigger coalitional killing of neighbours in chimpanzees, we also discuss them in light of chimpanzees' intraspecific interactions and territorial nature. Our findings may spur further research into the complexity of interspecies interactions. In addition, they may aid in combining field data from extant models with the Pliocene hominid fossil record to better understand behavioural adaptations and interspecific killing in the hominin lineage.

A great ape perspective on the origins and evolution of human viruses

Over the last two decades, the viromes of our closest relatives, the African great apes (AGA), have been intensively studied. Comparative approaches have unveiled diverse evolutionary patterns, highlighting both stable host-virus associations over extended evolutionary timescales and much more recent viral emergence events. In this chapter, we summarize these findings and outline how they have shed a new light on the origins and evolution of many human-infecting viruses. We also show how this knowledge can be used to better understand the evolution of human health in relation to viral infections.