Variation in monthly and seasonal elevation use impacts behavioral and dietary flexibility in Rhinopithecus bieti.

Black-and-white snub-nosed monkeys (Rhinopithecus bieti) rely on behavioral and dietary flexibility to survive in temperate latitudes at high-elevation habitats characterized by climate and resource seasonality. However, little is known about how elevation influences their behavioral and dietary flexibility at monthly or seasonal scales. We studied an isolated R. bieti population at Mt. Lasha in the Yunling Provincial Nature Reserve, Yunnan, China, between May 2008 and August 2016 to assess the impacts of elevation on feeding behavior and diet. Across our sample, R. bieti occupied elevations between 3031 and 3637 m above mean sea level (amsl), with a 315.1 m amsl range across months and a 247.3 m amsl range across seasons. Contrary to expectations, individuals spent less time feeding when ranging across higher elevations. Lichen consumption correlated with elevation use across months and seasons, with individuals spending more time feeding on this important resource at higher elevations. Leaf consumption only correlated with elevation use during the spring. Our results suggest that R. bieti do not maximize their food intake at higher elevations and that monthly and seasonal changes in lichen and leaf consumption largely explain variation in elevation use. These findings shed light on the responses of R. bieti to environmental change and offer insight into strategies for conserving their habitats in the face of anthropogenic disturbance.

Dynamic foraging strategy adaptation to heterogeneous environments contributes to social aggregation in snub-nosed monkeys.

The dynamics of animal social structures are heavily influenced by environmental patterns of competition and cooperation. In folivorous colobine primates, prevailing theories suggest that larger group sizes should be favored in rainforests with a year-round abundance of food, thereby reducing feeding competition. Yet, paradoxically, larger groups are frequently found in high-altitude or high-latitude montane ecosystems characterized by a seasonal scarcity of leaves. This contradiction is posited to arise from cooperative benefits in heterogeneous environments. To investigate this hypothesis, we carried out a six-year field study on two neighboring groups of golden snub-nosed monkey ( Rhinopithecus roxellana), a species representing the northernmost distribution of colobine primates. Results showed that the groups adjusted their movement and habitat selection in response to fluctuating climates and spatiotemporal variability of resources, indicative of a dynamic foraging strategy. Notably, during the cold, resource-scarce conditions in winter, the large group occupied food-rich habitats but did not exhibit significantly longer daily travel distances than the smaller neighboring group. Subsequently, we compiled an eco-behavioral dataset of 52 colobine species to explore their evolutionary trajectories. Analysis of this dataset suggested that the increase in group size may have evolved via home range expansion in response to the cold and heterogeneous climates found at higher altitudes or latitudes. Hence, we developed a multi-benefits framework to interpret the formation of larger groups by integrating environmental heterogeneity. In cold and diverse environments, even smaller groups require larger home ranges to meet their dynamic survival needs. The spatiotemporal distribution of high-quality resources within these expanded home ranges facilitates more frequent interactions between groups, thereby encouraging social aggregation into larger groups. This process enhances the benefits of collaborative actions and reproductive opportunities, while simultaneously optimizing travel costs through a dynamic foraging strategy.

Leopard predation on wild Sichuan snub-nosed monkeys.

Predation is widely recognized as a powerful selective pressure on primate behavior and ecology, although knowledge of predator-prey relationships remains limited partly due to the rarity of directly observed attacks on primates. Here, we describe four confirmed or suspected instances of leopard (Panthera pardus) predation on free-ranging Sichuan (golden) snub-nosed monkeys (Rhinopithecus roxellana), a highly endangered colobine species endemic to China. We recorded predation events and the reactions of monkey group members. We suggest that the evolution of a multilevel society may be an adaptive response by Sichuan snub-nosed monkeys to the risk from leopards as well as other potential predators, one that balances the pressures of predation and intra-species competition and conflict.

Maternal caretaking behavior towards a dead juvenile in a wild, multi-level primate society.

Maternal caretaking and transport of dead infants are widespread among nonhuman primates, having been reported in numerous species of monkeys and apes. By contrast, accounts of such behaviors toward dead juveniles are scarce. Here, we describe responses by the mother and other group members to the death of a juvenile in a wild, multi-level group of Sichuan snub-nosed monkeys (Rhinopithecus roxellana). Following the juvenile's fatal accident, his mother transported and cared for the corpse for four days. Immature monkeys belonging to the same one-male unit, and some individuals from other social units also showed interest in and tended the corpse. Comparisons of this case with those involving the deaths of infants and an adult female in the same population highlight possible effects of physiological, psychological and emotional factors in primate thanatological responses, and provide an additional perspective on the origin and evolution of compassionate acts.

Apparent diet digestibility of captive colobines in relation to stomach types with special reference to fibre digestion.

Colobine monkeys are known for the anatomical complexity of their stomachs, making them distinct within the primate order. Amongst foregut fermenters, they appear peculiar because of the occurrence of two different stomach types, having either three ('tripartite') or four ('quadripartite', adding the praesaccus) chambers. The functional differences between tri and quadripartite stomachs largely remain to be explained. In this study, we aim to compare the apparent digestibility (aD) in tripartite and quadripartite colobines. Hence, we measured the aD in two colobine species, Nasalis larvatus (quadripartite) and Trachypithecus cristatus (tripartite), in two zoos. We also included existing colobine literature data on the aD and analysed whether the aD of fibre components is different between the stomach types to test the hypothesis of whether quadripartite colobines show higher aD of fibre components than tripartite colobines did. Our captive N. larvatus specimen had a more distinctively varying nutrient intake across seasons with a larger seasonal variation in aD than that of a pair of T. cristatus, which mostly consumed commercial foods with a lower proportion of browse and less seasonal variation. We observed higher aD of dry matter (DM), neutral detergent fibre (NDF) and acid detergent fibre (ADF) in the N. larvatus specimen, suggesting a higher gut capacity of N. larvatus provided by the additional praesaccus forestomach chamber. Based on the analysis of literature data for aD, we also found that quadripartite species achieved higher fibre digestibility at similar dietary fibre levels compared with tripartite species, supporting the hypothesis that the additional gut capacity offered by the praesaccus facilitates a longer retention and hence more thorough microbial fermentation of plant fibre.

Human activities and elevational constraints restrict ranging patterns of snub-nosed monkeys in a mountainous refuge.

Both natural conditions and anthropogenic factors affect the survivability, distribution, and population density of wildlife. To understand the extent and how these factors drive species distributions, a detailed description of animal movement patterns in natural habitats is needed. In this study, we used satellite telemetry to monitor elevational ranges favored by endangered golden snub-nosed monkeys (Rhinopithecus roxellana), in the Qinling Mountains, central China. We investigated the abundance and distribution of food resources through sampling vegetation quadrats at different elevations and sampled anthropogenic activities using field surveys. Our results indicated that although there was no significant variation in food resources between low- (<1500 m) and middle-elevations (1500-2200 m), monkeys were found most often in areas above 1500 m, where there was less anthropogenic development (e.g. houses and roads); however, monkeys rarely ranged above 2200 m and had limited food availability at this altitude. There was limited human disturbance at this elevation. We suggest that both human activity and ecological constraints (i.e. food resources) have considerable effects on elevational use of R. roxellana in the Qinling Mountains. This study highlights the critical roles these factors can play in shaping the vertical distribution of high-altitude primates. This research provides useful insights for habitat-based conservation plans in which human disturbance management and habitat restoration should be prioritized.

Endozoochorous seed dispersal by golden snub-nosed monkeys in a temperate forest.

Seed dispersal is essential for plant recruitment and the maintenance of biodiversity. Colobine monkeys are primarily folivorous, but they also consume fruits and are often assumed to be seed predators. Although they are known to be epizoochorous seed dispersers, their role as endozoochorous seed dispersers needs reassessment. We examined potential endozoochory in golden snub-nosed monkeys (Rhinopithecus roxellana) at Dalongtan in Shennongjia National Park, central China, by assessing potential germination of ingested seeds (n = 1806, 9 species) from fecal samples. Intact seeds were in almost all fecal samples (ranging from 5-130 seeds), and ingested seeds were from small seeded species (seed width <4.5 mm). The 2 most abundant species were Actinidia arguta (73%) and Rosa caudata (15%). The fruits of A. arguta were unripe when ingested (i.e. effective seed predation) and the ingested seeds did not germinate in the trials. Therefore, ingestion of unripe seeds does not lead to effective seed dispersal. However, germination rates of defecated R. caudata (9%) were greater than control seeds (6% and 0%), demonstrating potential endozoochorous seed dispersal. Thus, colobine monkeys do indeed disperse mainly small-seeded from multi-seeded fruits through potential endozoochory and this process enhances the recruitment of seedlings.

Male social rank and food competition in a primate multi-level society.

OBJECTIVES: Social animals often have dominance hierarchies, with high rank conferring preferential access to resources. In primates, competition among males is often assumed to occur predominantly over reproductive opportunities. However, competition for food may occur during food shortages, such as in temperate species during winter. Higher-ranked males may thus gain preferential access to high-profitability food, which would enable them to spend longer engaged in activities other than feeding. MATERIALS AND METHODS: We performed a field experiment with a breeding band of golden snub-nosed monkeys, a species that lives in a multi-level society in high-altitude forests in central China. We provisioned monkey's high-profitability food during winter when natural foods are limited, and then recorded the times individual adult males spent engaged in different behaviors. RESULTS: Higher-ranking males spent less time feeding overall and fed on provisioned foods at a higher rate than lower-ranking males. Higher-ranking males therefore had more time to spend on alternative behaviors. We found no significant difference according to rank in times spent moving or resting. However, high-ranking males spend significantly longer on affiliative behaviors with other members of their social sub-units, especially grooming and being groomed, behaviors known to promote social cohesion in primates. DISCUSSION: We show that preferential access to high-profitability foods likely relaxes time-budget constraints to higher-ranking males. High-ranking males thus spend more time on non-feeding activities, especially grooming, which may enhance social cohesion within their social sub-unit. We discuss the potential direct and indirect benefits to high-ranking males associated with preferential access to high-value food during winter.

Eye Preference for Emotional Stimuli in Sichuan Snub-Nosed Monkeys.

This study presents the first evidence of effects of applying both positive and negative stimuli simultaneously on visual laterality in Old World monkeys. Thirteen captive individuals of Sichuan snub-nosed monkeys (Rhinopithecus roxellana) were chosen as focal subjects in the monocular box task. In total, 4 emotional categories (the preferred, the novel, the neutral, and the fearful) of visual stimuli were applied, and eye preference was recorded when individuals looked at each stimulus through an observation hole in the box. We found evidence of visual laterality at the individual level, but not at the group level for each stimulus. For the preferred stimulus, 9 individuals showed significant right-eye preference while 4 individuals showed significant left-eye preference. For the other 3 stimuli, 7 individuals displayed significant right-eye preference while 6 individuals displayed significant left-eye preference. Totally, 11 of 13 individuals showed consistency in the visual laterality direction (7 right-eye preference and 4 left-eye preference) across the 4 stimuli. The remaining 2 individuals displayed right-eye preference for the preferred stimulus while they showed left-eye preference for the other 3 stimuli. There was no significant difference among various stimuli regarding the direction of visual laterality. However, there was a significant difference in the strength of visual laterality among various stimulus categories. The strength of visual laterality for the preferred stimulus was significantly lower than that for the other 3 stimuli. The strength of visual laterality for the fearful stimulus was significantly higher than that for the novel stimulus and the neutral stimulus. Furthermore, the looking duration for the preferred stimulus was significantly higher than that for the other 3 stimuli. The looking duration for the novel stimulus was significantly higher than that for the neutral stimulus and the fearful stimulus. The looking duration for the neutral stimulus was significantly higher than that for the fearful stimulus. Our findings indicate emotional valence of stimuli significantly influence eye looking duration and the strength of visual laterality but not for the direction of visual laterality in this species. Taken together, emotional valence of stimuli plays an important role in the eye use of R. roxellana.

Living in forests: strata use by Indo-Chinese gray langurs ( Trachypithecus crepusculus) and the effect of forest cover on Trachypithecus terrestriality.

Studies on behavioral flexibility in response to habitat differences and degradation are crucial for developing conservation strategies for endangered species. Trachypithecus species inhabit various habitats and display different patterns of strata use; however, the effect of habitat structure on strata use remains poorly studied. Here, we investigated strata use patterns of Indo-Chinese gray langurs ( Trachypithecus crepusculus) in a primary evergreen forest in Mt. Wuliang, southwest China, from June 2012 to January 2016. In addition, we compared T. crepusculus strata use and terrestriality with five other Trachypithecus species from previous studies. Unlike langurs living in karst forests, our study group was typically arboreal and spent only 2.9% of time on the ground. The group showed a preference for higher strata when resting and lower strata (<20 m) when moving. The langurs primarily used time on the ground for geophagy, but otherwise avoided the ground during feeding. These strata use patterns are similar to those of limestone langurs ( T. francoisi) when using continuous forests. At the genus level ( n=6 species), we found a negative relationship between habitat forest cover and terrestriality. This negative relationship was also true for the five limestone langur species, implying limestone langurs increase territoriality in response to decreased forest cover. Our results document behavioral flexibility in strata use of Trachypithecus langurs and highlight the importance of the protection of continuous forests to promote langur conservation.

Enamel chipping in Taï Forest cercopithecids: Implications for diet reconstruction in paleoanthropological contexts.

Antemortem enamel chipping in living and fossil primates is often interpreted as evidence of hard-object feeding (i.e., 'durophagy'). Laboratory analyses of tooth fracture have modeled the theoretical diets and loading conditions that may produce such chips. Previous chipping studies of nonhuman primates tend to combine populations into species samples, despite the fact that species can vary significantly in diet across their ranges. Chipping is yet to be analyzed across population-specific species samples for which long-term dietary data are available. Here, we test the association between enamel chipping and diet in a community of cercopithecid primates inhabiting the Taï Forest, Ivory Coast. We examined fourth premolars and first molars (n = 867) from naturally deceased specimens of Cercocebus atys, Colobus polykomos, Piliocolobus badius,Procolobus verus, and three species of Cercopithecus. We found little support for a predictive relationship between enamel chipping and diet across the entire Taï monkey community. Cercocebus atys, a dedicated hard-object feeder, exhibited the highest frequencies of (1) chipped teeth and (2) chips of large size; however, the other monkey with a significant degree of granivory, Co. polykomos, exhibited the lowest chip frequency. In addition, primates with little evidence of mechanically challenging or hard-food diets-such as Cercopithecus spp., Pi. badius, and Pr. verus-evinced higher chipping frequencies than expected. The equivocal and stochastic nature of enamel chipping in the Taï monkeys suggests nondietary factors contribute significantly to chipping. A negative association between canopy preference and chipping suggests a role of exogenous particles in chip formation, whereby taxa foraging closer to the forest floor encounter more errant particulates during feeding than species foraging in higher strata. We conclude that current enamel chipping models may provide insight into the diets of fossil primates, but only in cases of extreme durophagy. Given the role of nondietary factors in chip formation, our ability to reliably reconstruct a range of diets from a gradient of chipping in fossil taxa is likely weak.

Decision-making process during collective movement initiation in golden snub-nosed monkeys (Rhinopithecus roxellana).

Collective decision-making is important for coordination and synchronization of the activities among group-living animals and the mechanisms guiding such procedure involve a great variety of characteristics of behavior and motivation. This study provides some evidence investigating collective movement initiation in a multi-level social band of the golden snub-nosed monkeys (Rhinopithecus roxellana) located in the Mts. Qinling, China. We collect 1223 datum records relevant to decision initiation from six OMUs. The results indicate that collective movement initiation could be divided into two continual but relatively independent processes: decisions on moving direction and movement implementation. In both processes, adult individuals are more likely to initiate the decision-making, while other adults vote on initiator's preference, with a threshold, a supporting number required for a success. Thus, voting behavior and quorum fulfillment contribute to a successful decision-making. Adult individuals play important role in making decisions for moving direction and implementation. For a successful collective movement initiation, the individuals being more central in grooming network initiate decisions more frequently than the others, and attract voters more easily. Furthermore, following the initiation, at least four positive voters are required for a direction decision and at least three positive voters are needed for the decision on movement implementation, which could be considered as the threshold of quorum numbers required for a successful decision. This study has provided some very interesting information and scientific evidence in understanding social structure and behaviors of the nonhuman primates with a social structure very similar to humans'. Thus, some results can directly be referred to the comprehension of human social structure and behavior.

Using unmanned aerial vehicles with thermal-image acquisition cameras for animal surveys: a case study on the Sichuan snub-nosed monkey in the Qinling Mountains.

Following significant developments in technology, alternative devices have been applied in fieldwork for animal and plant surveys. Thermal-image acquisition cameras installed on unmanned aerial vehicles (UAVs) have been used in animal surveys in the wilderness. This article demonstrates an example of how UAVs can be used in high mountainous regions, presenting a case study on the Sichuan snub-nosed monkey with a detection rate of 65.19% for positive individual identification. It also presents a model that can prospectively predict population size for a given animal species, which is based on combined initial work using UAVs and traditional surveys on the ground. A great potential advantage of UAVs is significantly shortening survey procedures, particularly for areas with high mountains and plateaus, such as the Himalayas, the Qinghai-Tibet Plateau, Hengduan Mountains, the Yunnan-Gui Plateau and Qinling Mountains in China, where carrying out a traditional survey is extremely difficult, so that species and population surveys, particularly for critically endangered animals, are largely absent. This lack of data has impacted the management of endangered animals as well as the formulation and amendment of conservation strategies.

Comparison of Activity Budgets, Diet, and Habitat Utilization between Provisioned and Wild Groups of the François' Langur (Trachypithecus francoisi) in Mayanghe National Nature Reserve, China.

The endangered François' langur (Trachypithecus francoisi) is only found from southern China to northeastern Vietnam. This study evaluates behavioral differences between provisioned (Ts, 7 individuals) and wild (Tn, 13 individuals) family groups in Mayanghe National Nature Reserve, China. Scan sampling every 5 min for 12 h daily between the months of March 2013 and February 2014 was used to record behaviors in seven categories. Tn exhibited three main feeding periods daily, whereas Ts showed more variable behavioral patterns that relied on provisions. The Tn alpha male showed twice the amount of guarding behavior compared with the Ts alpha male. The proportion of each habitat type utilized differed significantly between Tn and Ts (χ2[4] = 17,131.4, p < 0.01). Additionally, dietary diversity differed between the two groups: Tn fed on 61 plant species, whereas Ts fed on 43 plant species. Tn rarely ate sweet potato and corn other than discarded remnants of human food (0.2% of their total food sources), whereas these foods represented 21.8% of Ts food sources. We compared data for the two troops to understand this species' activities under human interference, in particular to determine whether provisioning is a suitable strategy for their conservation.

Reproductive Parameters of Wild Rhinopithecus bieti.

Animal life activities are rhythmic and affected by seasonal periodicity. Based on 9 years of observations, we estimated the reproductive parameters of a wild, but provisioned Yunnan snub-nosed monkey (Rhinopithecus bieti) group at Xiangguqing in Baimaxueshan National Nature Reserve, Yunnan Province, China. We observed 84 infants (43 males and 41 females) from 41 females between 2010 and 2018. We found the birth sex ratio was 1:1, the female age at first birth was 6.13 years and infant mortality was about 15.5%. Nine years of data showed that the maximum birth season lasted 126 days, and the average length per year was 98.57 ± 18.71 days. R. bieti,characterized by strictly seasonal reproduction, started giving birth on February 1, and this ended on June 7, with a peak reached from March 4 to March 11 (10th week). The mean birth date was March 20 (79.21 ± 29.54 days), and the median birth date was March 11 (71st day). The mean interbirth interval (IBI) was approximately 2 years, and the IBIs among females whose infants had survived for 1 year were found to be significantly longer than those found in females who lost their infant within 1 year. Comparing the reproduction parameters among Asian and African colobines, we concluded that Asian and African colobines tend to have an IBI of 2 years or more, females tend to give birth at the age of 5-6 years, Rhinopithecus species had a strict seasonal reproductive pattern concentrated in February to April. Seasonal changes in food resources and climatic factors may be the main reasons for the variation in reproductive parameters in intraspecific and interspecific comparisons of Asian and African colobines.

Effect of Group Size on Time Budgets and Ranging Behavior of White-Headed Langurs in Limestone Forest, Southwest China.

The ecological constraints model is well supported by data from most frugivorous primates; however, the prediction power of the model is weak for folivorous primates. From September 2016 to August 2017, we collected comparative data on time budgets, daily path lengths and diets of four groups of white-headed langurs (Trachypithecus leucocephalus), including two large groups (G-DS and G-ZWY) and two small groups (G-LZ and G-NN) in Chongzuo White-Headed Langur National Nature Reserve, Guangxi Province, Southwest China. The aim was to obtain evidence of foraging competition and to test the ecological constraints model on this highly folivorous primate in its karst habitat. The results showed that langurs in the larger groups spent more time traveling, less time resting, and had a longer average daily path length than those in the small groups. Diet composition and dietary diversity were not significantly different between the large and small groups. Our study demonstrates that langurs from large groups suffer scramble competition in limestone forests and supports the validity of the ecological constraints model for folivores.

Positional Behaviours of François' Langur (Trachypithecus francoisi) in the Limestone Forest of Nonggang, Guangxi, South-West China.

Primates' positional behaviours provide information for understanding relationships among morphology, ecology and behavioural flexibility. From September 2005 to August 2006, we collected data via instantaneous scan sampling on positional behaviours in François' langurs at Nonggang Nature Reserve, south-west China. We predicted that these langurs would use (1) leaping as the predominant locomotor mode and (2) bipedal standing more frequently in the rainy season than in the dry season. Our result showed that leaping was the dominant locomotor mode (38.38%), followed by -quadrupedal walking (31.2%), vertical climbing (25.1%) and quadrupedal running (5.3%). The ground was the most frequently used stratum during movement (33.4%). Most locomotion through trees occurred on small- (48.7%) and medium-sized (47.6%) substrates. Locomotor mode, forest stratum use and substrate use during movement did not vary seasonally. When stationary, sitting was the most common posture (92.1%), followed by bipedal standing (3.7%), lying (3.5%), quadrupedal standing (0.6%), suspending (0.2%) and back-lying (<0.1%). Posture varied significantly with the season. During resting, langurs used sitting and bipedal standing more frequently in the dry season, while adopting lying more frequently in the rainy season. During feeding, sitting was adopted more frequently in the rainy than in the dry season, whereas bipedal standing was used more frequently in the dry season. Langurs spent more feeding time on the ground in the dry than in the rainy season. Locomotor patterns in François' langurs are likely linked to morphological and anatomical characteristics, along with the limestone forest's structure. Our result completely supported prediction 1 but not prediction 2. This study suggests that seasonal variation in positional behaviour might result from the temporal difference in spatial distribution of foods and behavioural thermoregulation strategy. We found that François' langurs adjusted positional behaviour in response to seasonality, and this behavioural flexibility allows them to survive in a variety of habitats, including limestone forests.

Altitude and human disturbance are associated with helminth diversity in an endangered primate, Procolobus gordonorum.

Gastrointestinal parasites colonizing the mammalian gut influence the host immune system and health. Parasite infections, mainly helminths, have been studied intensively in both humans and non-human animals, but relatively rarely within a conservation framework. The Udzungwa red colobus monkey (Procolobus gordonorum) is an endangered endemic primate species living in the Udzungwa Mountains of Tanzania, a global biodiversity hotspot. Since this endemic primate species is highly sensitive to human disturbance, here we investigate whether habitat type (driven by natural and human-induced factors) is associated with helminth diversity. Using standard flotation and sedimentation techniques, we analyzed 251 fecal samples belonging to 25 social groups from four different forest blocks within the Udzungwa Mountains. Five parasitic helminth taxa were recovered from Udzungwa red colobus, including Trichuris sp., Strongyloides fulleborni, S. stercoralis, a strongylid nematode and Colobenterobius sp. We used Generalized Linear Mixed Models to explore the contribution of habitat type, altitude and fecal glucocorticoid levels (as biomarkers of stress) in predicting gut parasite variation. Although some parasites (e.g., Trichuris sp.) infected more than 50% of individuals, compared to others (e.g., Colobenterobius sp.) that infected less than 3%, both parasite richness and prevalence did not differ significantly across forests, even when controlling for seasonality. Stress hormone levels also did not predict variation in parasite richness, while altitude could explain it resulting in lower richness at lower altitudes. Because human activities causing disturbance are concentrated mainly at lower altitudes, we suggest that protection of primate forest habitat preserves natural diversity at both macro- and microscales, and that the importance of the latter should not be underestimated.

Suitable habitat prediction of Sichuan snub-nosed monkeys (Rhinopithecus roxellana) and its implications for conservation in Baihe Nature Reserve, Sichuan, China.

As an endemic primate species with one of the highest priorities in wildlife conservation in China, Sichuan snub-nosed monkeys (Rhinopithecus roxellana) have undergone a sharp decline and range reduction in recent centuries. Here, we used maximum entropy modelling (MaxEnt) integrated with four types of environmental variables, including three biological climate variables (Bio17, precipitation of the driest quarter; Bio6, min. temperature of the coldest month; and Bio2, mean diurnal range), three topographic variables (altitude, slope, and aspect), two anthropogenic variables (Human Footprint Index and human disturbance), and three vegetation-related variables (enhanced vegetation index, normalized difference vegetation index, and Wet Index) to identify the spatial distribution of suitable habitats for Sichuan snub-nosed monkeys in Baihe Nature Reserve (BNR), which is located in the Minshan Mountains. The average training AUC of our model performance is 0.929 ± 0.003. The model predicted 9.6 km2 of high suitability habitats and 14.1 km2 of moderate suitability habitats for Sichuan snub-nosed monkeys, adding up to only 11.7% of the total area of concern for the study in the BNR. The top four variables ranked in the model (altitude, Human Footprint Index, human disturbance, and Bio17) accounted for relative gain contributions of 23.3%, 19.3%, 14.2%, and 13.4%, respectively. The predicted suitable habitats were confined to an altitude range of 1971-3198 m, Human Footprint Index of mainly 3-5 values, low human disturbance (mainly livestock), and precipitation of the driest (or coldest) quarter of 9-22 mm. Additionally, the suitable habitats were mainly distributed in the core zone (36.1%), buffer zone (26.8%), and experimental zone (29.5%). The remaining habitats (7.6%) were distributed in the 0.5-km buffer zone of the reserve border. The predicted suitable habitats indicated limited suitable habitat space for the Sichuan snub-nosed monkeys, with most of the suitable habitat distributed outside the core zone in the BNR. Our findings highlighted that human activities in all three functional zones could be the most negative factor on suitable habitat distribution of Sichuan snub-nosed monkeys in the BNR.

Colobine forestomach anatomy and diet.

Colobine monkeys have complex, multichambered, foregut-fermenting stomachs with either three ("tripartite") or four ("quadripartite," adding the praesaccus) chambers where a commensal microbiome digests plant cell walls and possibly detoxifies defensive plant chemicals. Although different potential functions for the praesaccus have been suggested, little evidence exists to support any of the proposed functions. To address the issue of the function of the praesaccus, we collated literature data on diet and compared tripartite and quadripartite species. Our results suggest that the praesaccus is an adaptation to a dietary niche with a particularly high reliance on leaves as fallback foods in colobine clades with quadripartite stomachs, and a higher reliance on fruits/seeds as foods at times of high fruit availability in clades with tripartite stomachs. This supports the notion that a large gut capacity is an important characteristic by which folivores survive on a high fiber diet, and that this large gut capacity may not be necessary for some species if there are seasonal peaks in fruit availability.