International Journal of Primatology最新文献

The ability of primates to make decisions by integrating sensory information, memories about their environment, and social factors may have played a role in the evolution of primate cognition. However, we know little about the ability of lemurs to consider multiple aspects of a problem. We conducted experiments on the use of memory and olfaction in 11 groups of captive brown lemurs (Eulemur spp). We placed six or nine containers, 1/3 of which we baited with two pieces of cantaloupe, in consistent locations in the lemurs’ enclosures. We used two schedules for five initial trials, with delays of 2 h or 1 day (i.e., with nocturnal sleep) between trials. We conducted subsequent trials after 1, 2, 4, 5, 7, and 14 days. We recorded the order in which lemurs investigated and opened containers. We also noted social interactions, scent marking, and the number of pieces of cantaloupe eaten. The probability that lemurs would investigate baited containers before empty containers increased from chance levels on the first trial to approximately 0.5 above chance by the 6th and later trials, indicating the use of memory. The initial schedule did not significantly affect performance. Lemurs opened 98% (273 of 278) of baited containers before empty containers, indicating the use of olfaction at close range. They scent-marked in the proximity of only 10% of baited containers. Dominant status and being first to investigate baited containers positively impacted cantaloupe consumption. The results suggest that the lemurs integrated spatial memory, olfactory cues, and social information in decision-making.

Determining primate geographic ranges is essential for understanding their ecology and developing their conservation policies, but it is particularly challenging for rare, cryptic, or widely distributed species. Science-based methods and Indigenous and local knowledge have mutually contributed to addressing this conundrum. Here, we report on a new camera-trap record of a solitary mandrill (Mandrillus sphinx) in Nki National Park, southeast Cameroon, and interviews with Baka people about encounters with mandrills. We placed 481 camera traps for 32,644 total days, obtaining one video of an adult male mandrill on 19 April 2021, 20.2 km north of the Dja River. We also interviewed 30 Baka people from two neighboring villages about their experiences of observing mandrills. Seven interviewees responded that they had observed mandrills in this area: three reported solitary males, and four reported large groups. All observations were in areas >30 km south of the villages and >20 years ago. The results suggest the presence, but also the rarity, of mandrills in this area, where only solitary males may range outside the species geographic distribution, possibly temporarily. However, we cannot conclude that large groups of mandrills are absent in this area because people are not allowed to stay in the park, so the Baka people’s knowledge of the remote areas has been severely limited. To determine the accurate distribution of primates and develop effective conservation actions, we need collaborative research and conservation platforms that further connect Indigenous and local people with scientists.

The ingestion of bark has been observed across the animal kingdom and is well documented in free-ranging chimpanzees. Thus far, the best-supported hypothesis for the adaptive function of this behavior is the fallback food hypothesis, which asserts that chimpanzees consume bark and cambium when preferred foods are scarce. However, alternative explanations exist, including the essential nutrient and mineral hypothesis, the self-medication hypothesis, and the stressed-tree hypothesis. We tested whether the fallback food hypothesis can explain bark-feeding across two communities of Eastern chimpanzees (Pan troglodytes schweinfurthii) in the Budongo Forest, Uganda. We used 13 years of the site’s long-term behavioral data, 5 years of food availability data, and 8 months of direct and indirect observations. We also conducted eight 400-m line transects to collect data on the distribution of tree species across community home ranges. We employed several analyses, including Pearson correlation tests, qualitative comparisons of descriptive data and heat maps, and interpretation of behavioral anecdotes. We found varying patterns of bark-feeding seasonality across tree species, with bark-feeding on several species showing no correlation with food scarcity. We also identified differences in the amounts of bark targeted between tree species and report anecdotal evidence of chimpanzees prioritizing bark over high-value foods. Lastly, we found that bark-feeding on certain species disproportionally occurs far from community core areas, despite relative abundance of these species within the home range. As a result, we argue that the fallback food hypothesis cannot explain bark-feeding across all tree species. Instead, we present supporting evidence for several alternative hypotheses, including self-medication, thereby challenging the widely accepted function of this behavior.

Sleep and sleep-related behaviors are integral components of primate behavior and ecology that are linked to various habitat-specific factors and often are modified in response to environmental fluctuations and threats. Despite the growing literature on primates, information on sleep-related behaviors of tarsiers remains sparse, especially for Philippine tarsiers, where our current understanding is hampered by the paucity of studies on wild populations. We radio-tracked eight Philippine tarsiers inhabiting a protected forest fragment between December 2016 and February 2018 to assess their sleeping site selection, sleep-related positional behavior, and social system. From 266 instantaneous sampling bouts, where each tarsier was observed a maximum of once per day, we found that the tarsiers frequently used trees with thickets of lianas and at least 15 plant species as sleeping sites. They slept from ground level to above 8 m, with most sightings at 3 to 6 m, and recurrent detections above 8 m, and preferred a flexed resting posture, on angled or horizontal, small-sized lianas or branches. Although frequently solitary, they also slept in pairs and in small groups of up to four individuals. We inferred polygyny based on observations of one adult male who associated and huddled with two nonassociated adult females, and direct male care through huddling and accompaniment. Our study revealed increased height use and gregariousness not previously described for Philippine tarsiers, shedding light on potential flexible behaviors by nocturnal primates in fragmented landscapes. Sleep-related behaviors present another avenue of research that has important implications on their conservation.

Sympatric primate species coexist in tropical communities through interactions with the abiotic environment and other species. Determining the factors that influence primate species co-occurrence can help to inform conservation practices. Our study focused on the ecological interactions of central chimpanzees (Pan troglodytes troglodytes) and western lowland gorillas (Gorilla gorilla gorilla) with each other and their environment in a multiuse landscape. We assessed species-specific occupancy at 17 camera trap sites across different land-use types (National Park, Forest Management Units, or Community Lands) between June 2019 and May 2020 and examined the impact of fruit availability and human presence on ape presence. Across the study area, chimpanzees occupied a greater total number of sites than did gorillas, with a significantly higher proportion of occupied sites within the National Park than in other land-use types. The density of fruiting trees positively influenced the presence of gorillas but had no effect on chimpanzee presence. We found no effect of human presence on the presence of either chimpanzees or gorillas, although this analysis was limited to sites where apes were present. The probability of either species being present at a site during a given month remained stable under the conditional presence or absence of the other species, suggesting the absence of interactions between the two species at our study sites. These results support previous findings that the heterogeneous distribution of fruits and preferred resources allows chimpanzees and gorillas to limit direct competition by exploiting different feeding resources. Our findings provide insights on the factors influencing the occupancy of each species, including environmental variables and land-use type, information relevant when monitoring their coexistence within tropical communities.

Habitat destruction, land conversion, and forest fragmentation over the past several decades have resulted in major declines and local extirpation of wild animal and plant species. The gray snub-nosed monkey (Rhinopithecus brelichi) is currently listed among the 25 most endangered primate species in the world, with an estimated remaining wild population of less than 400 individuals. Given the potential negative effects of small population size on genetic diversity, we investigated how factors, such as climate, inbreeding, kinship, population structure, and effective population size, have contributed to their genetic status. We extracted DNA from 307 fecal samples and analyzed microsatellite diversity, sex-identifying genes, and the mtDNA control region in 179 wild individuals. Our analyses suggest that gray snub-nosed monkeys experienced an initial population decline during the Last Glacial Maximum, some 20,000 years ago. During the past 70 years, this species experienced a second, steeper population decline, coinciding with human activities. Their current effective population size (± SD) of 675 ± 292 exceeds the remaining number of individuals in the population and has declined by 93.9%—96.7% over the past 20,000 years. Our findings highlight the need for immediate conservation and management strategies to protect this endemic and Critically Endangered primate species.

Post-conflict behaviors are a crucial component of primate sociality, yet are difficult to study in the wild. We evaluated the presence and timing of reconciliation, victim-solicited and unsolicited third-party affiliation, and secondary and redirected aggression following observed agonistic interactions among 38 wild gelada monkeys (Theropithecus gelada) in eight one-male, multi-female units at Guassa, Ethiopia, from April to August 2018. We also report background rates of aggression and patterns of agonistic interactions and post-conflict behaviours among wild geladas relative to possible mediating factors for each conflict, including social rank disparity, kinship type, sex, age class, conflict intensity, and conflict decidedness. Across 55 post-conflict and 55 subsequent matched-control focal follows, we found no evidence for post-conflict reconciliation, third-party affiliation, secondary aggression, or redirected aggression. These findings contrast with previous studies of captive geladas, which find that individuals often reconcile after fights and frequently exhibit unsolicited third-party affiliation when reconciliation does not occur. Our results from wild geladas point to possible populational differences in behavioral tendencies arising from variable space, time, social grouping, and/or food availability constraints. Our findings also reveal potential limitations in applying identical data collection protocols across environmental contexts and underscore the importance of creating generalizable cross-context metrics to better understand, and contextualize, the diversity of post-conflict behavioral mechanisms underpinning primate sociality in geladas and other group-living primates.

Multilevel social organizations necessitate close spatial proximity of social units, making dominance hierarchies between core units potentially important to control aggression. We examined whether an interunit dominance hierarchy was present for a Rwenzori Angolan colobus multilevel society (MLS) and its potential social correlates. We recorded the outcome of interunit interactions (IUIs, N = 167) over 59 days in a band of 14 core units at Nabugabo, Uganda. Core units were almost always closely clustered, so we defined IUIs as approaches that decreased the distance between units and lead to changes in behaviour. We assessed dominance using network-based ranking, because the hierarchy was not linear. Tiers of dominance were evident, and we examined these relative to demographics, clan identity (MLS tier 2), male anogenital distance (AGD – a correlate of in utero androgen exposure), and social network analyses (SNA) of interunit association. Unit displacements without aggression occurred in 31.7% of IUIs, and some aggression occurred in 64.7%. Dominance tier was not significantly associated with unit demographics, but units with males that had longer AGDs (more androgenized) tended to be more dominant. Social network analyses showed that higher-ranking units had greater strength, eigenvector centralities, and clustering coefficients than lower-ranking units. Interunit interactions between units in different clans were more aggressive than those within clans and clan identity correlated with dominance tier, indicating that one clan outranked the other. Overall, we demonstrate complex social and spatial factors determining priority-of-access to resources in a primate MLS.

Climatic changes with unpredictable weather conditions have negative effects on many primates. With several lemur species reaching their ecological limits in the dry and hypervariable spiny forest, Madagascar might provide an example for understanding adaptations of primates to unpredictable conditions. Here, we aimed to identify vegetation characteristics that allow Lepilemur petteri to persist in an environment at the limit of its ecological niche. For this, we linked the patchy distribution of the species to vegetation characteristics described on the ground and by remote sensing reflecting primary production (Enhanced Vegetation Index from MODIS) for 17 sites in nine regions, spread over 100 km along Tsimanampetsotse NP. We verified the results on a smaller scale by radio-tracking and vegetation analyses related to home ranges of 13 L. petteri. Remote sensing indicated that L. petteri is more likely to occur in forests where the variation of the annual primary production and the interannual variability of the month with the lowest primary production are low.

Lepilemur petteri was more likely to occur with increasing densities of large trees, large food tree species (diameter ≥ 10 cm) and octopus trees (Alluaudia procera). Alluaudia procera provide food year-round and shelter in the spiny forest where large trees with holes are absent. High tree species diversity might buffer food availability against failure of certain tree species to produce food. These findings illustrate limiting constraints of climatic hypervariability for lemurs and indicate benefits of forest restoration with high numbers of tree species for biodiversity conservation.