Habitat suitability analysis reveals high ecological flexibility in a "strict" forest primate.

BACKGROUND: Research of many mammal species tends to focus on single habitats, reducing knowledge of ecological flexibility. The Javan lutung (Trachypithecus auratus) is considered a strict forest primate, and little is known about populations living in savannah. In 2017-2018, we investigated the density and distribution of Javan lutung in Baluran National Park, Indonesia. We conducted ad libitum follows and line transect distance sampling with habitat suitability analysis of Javan lutung. RESULTS: Estimated density was 14.91 individuals km- 2 (95% CI 7.91-28.08), and estimated population size was 3727 individuals (95% CI 1979 - 7019). Long-tailed macaque (Macaca fascicularis) habitat suitability was the main driver of lutung habitat suitability as the probability of lutung occurrence increased greatly with macaque habitat suitability. Distance to roads, and distance to secondary forest had a negative relationship with lutung occurrence. Lutung habitat suitability decreased with increasing elevation, however, Mt Baluran and the primary forest on Mt Baluran was under-sampled due to treacherous conditions. Follows of six focus groups revealed considerable use of savannah, with terrestrial travel. The follows also revealed polyspecific associations with long-tailed macaques through shared sleeping sites and inter-specific vocalisations. CONCLUSIONS: Our study provides new knowledge on the general ecology of Javan lutung, such as use of savannah habitats, underlining our need to branch out in our study sites to understand the flexibility and adaptability of our study species. Another undocumented behaviour is the polyspecific association with long-tailed macaques. We encourage more research on this subject.

Dietary Variation in Diana Monkeys (Cercopithecus diana): The Effects of Polyspecific Associations.

Establishing dietary central tendencies and extremes remains an important goal of primate research. While habitat differences and spatial discontinuity are well-documented contributors to dietary variation, other factors including polyspecific associations may significantly impact diet through changes in strata use and/or increased feeding competition. Here, we examine polyspecific association with closely related species as a source of dietary variation in a rain forest primate. Diana monkeys (Cercopithecus diana) in Côte d'Ivoire's Taï Forest frequently participate in mixed-species groups. We use data collected over a 5-year period on 4 Diana monkey groups to examine how association affects group diets. Groups exhibited significant differences in association rates with other guenon species, but this minimally influenced diet when food categories (fruit, invertebrates, leaves) were compared: diet overlap of 4 groups across the study period ranges from 90.8 to 98.1%. Examination of species composition within food categories is more revealing: intergroup dietary overlap decreases to 69.8-79.4% across the study period when comparing species contributing to total frugivory and folivory. These data support earlier findings that Diana monkeys maintain fruit-rich diets by competitively excluding sympatric congeners while highlighting that even selective frugivores such as Diana monkeys may exhibit remarkable dietary flexibility. Our study underscores the fact that broad categorical labels can obscure significant dietary differences.

Mixed-species associations in cuxiús (genus Chiropotes).

Polyspecific or mixed-species associations, where two or more species come together to forage and travel as a unit, have been reported in many primate species. These associations appear to offer a number of benefits to the species involved including increased foraging efficiency and decreased risk of predation. While several researchers have suggested that cuxiús (genus Chiropotes) form mixed-species associations, previous studies have not identified the circumstances under which cuxiús form associations or whether they form associations more often than would be expected by chance. Here we present data on the formation of mixed-species associations by four species of cuxiús at eight different sites in Brazil, Suriname, and Guyana. We analyzed data from two of the study sites, (Biological Dynamics of Forest Fragments Project (BDFFP), Brazil and the Upper Essequibo Conservation Concession (UECC), Guyana, to assess whether associations occurred more than would be expected by chance encounters and identify the factors influencing their formation. Cuxiús showed a high degree of inter-site variation in the frequency of time spent in association (ranging from 2 to 26% of observation time) and duration of associations (mean duration from 22 min to 2.5 hr). Sapajus apella was the most common association partner at most sites. At BDFFP, cuxiús formed associations more frequently but not for longer duration than expected by chance. For much of the year at UECC, associations were not more frequent or longer than chance. However, during the dry season, cuxiús formed associations with S. apella significantly more often and for longer duration than predicted by chance. Cuxiús at UECC formed associations significantly more often when in smaller subgroups and when foraging for insects, and alarm called significantly less frequently during associations. We suggest cuxiús form mixed-species associations at some sites as an adaptive strategy to decrease predation risk and/or increase foraging efficiency.

Oral Processing of Three Guenon Species in Taï National Park, Côte d'Ivoire.

Three guenon species in Taï National Park frequently form and maintain stable polyspecific associations despite significant feeding competition. This dietary overlap provides an opportunity to examine how closely related and anatomically similar taxa process the same foods. Our research examines whether the oral-processing behaviors of these guenons differ when they consume the same foods. Methods: Data on oral-processing behavior were collected on one habituated group each of Cercopithecus campbelli, C. diana, and C. petaurista in Taï National Park, Côte d'Ivoire from January 2016 to December 2018. We recorded the frequency with which foods were introduced to the mouth (ingestive action) and the frequency with which foods were processed using incisors, canines, and postcanine teeth. Oral-processing profiles for species-specific plant foods, fungi, and invertebrates were compared using Monte Carlo resampling. We quantified oral-processing behavior during a total of 2316 five-minute focal periods. Diana monkeys use their incisors significantly more per ingestive action than Campbell's monkeys or Lesser spot-nosed guenons. Lesser spot-nosed guenons use their incisors more than Campbell's monkeys. Diana monkeys also use significantly more post-canine chews per ingestive action than Campbell's monkeys and Lesser spot-nosed guenons. Lesser spot-nosed guenons generally use fewer post-canine chews than Diana monkeys but more than Campbell's monkeys. Canine use during feeding was rare in all three taxa. The three study species use different oral-processing profiles when consuming the same foods. These results are intriguing given the overall similarity in dental and cranial anatomy in these taxa. The oral-processing profiles we report do not encompass the full dietary breadth of all species; however, the behavioral diversity demonstrated during consumption of the same foods suggests that insight into feeding behavior is more likely obtained by examining oral processing of individual foods rather than broad food categories. Furthermore, these results underscore that important variation in feeding behavior is not necessarily associated with morphological differences in dental or craniofacial anatomy.

Mixed-species groups of Serengeti grazers: a test of the stress gradient hypothesis.

Understanding the role of species interactions within communities is a central focus of ecology. A key challenge is to understand variation in species interactions along environmental gradients. The stress gradient hypothesis posits that positive interactions increase and competitive interactions decrease with increasing consumer pressure or environmental stress. This hypothesis has received extensive attention in plant community ecology, but only a handful of tests in animals. Furthermore, few empirical studies have examined multiple co-occurring stressors. Here we test predictions of the stress gradient hypothesis using the occurrence of mixed-species groups in six common grazing ungulate species within the Serengeti-Mara ecosystem. We use mixed-species groups as a proxy for potential positive interactions because they may enhance protection from predators or increase access to high-quality forage. Alternatively, competition for resources may limit the formation of mixed-species groups. Using more than 115,000 camera trap observations collected over 5 yr, we found that mixed-species groups were more likely to occur in risky areas (i.e., areas closer to lion vantage points and in woodland habitat where lions hunt preferentially) and during time periods when resource levels were high. These results are consistent with the interpretation that stress from high predation risk may contribute to the formation of mixed-species groups, but that competition for resources may prevent their formation when food availability is low. Our results are consistent with support for the stress gradient hypothesis in animals along a consumer pressure gradient while identifying the potential influence of a co-occurring stressor, thus providing a link between research in plant community ecology on the stress gradient hypothesis, and research in animal ecology on trade-offs between foraging and risk in landscapes of fear.

Mixed flocks and polyspecific associations: Costs and benefits of mixed groups to birds and monkeys.

This review examines the diversity of avian mixed foraging flocks with the goal of relating the conclusions to primate polyspecific associations. Mixed associations are considered as adaptations for achieving an optimal balance between predator protection and feeding efficiency. In open habitat, predator and prey are able to detect each other at a distance and feeding competition is low, especially in species that subsist on a homogeneously distributed food supply. These conditions favor large groups of variable composition. In closed habitats, predators attack at close range, so early warning alarm systems are at a premium. Feeding competition is often intense because food resources such as fruit, flushing leaves, and nectar are spatially concentrated. Since feeding competition is generally less between than within species, these conditions favor mixed associations composed of small numbers of several to many species, and the evolution of elaborate early warning systems to thwart predators. The primate polyspecific associations that have been studied to date share characteristics with the closed habitat model while exhibiting some important distinctions. Primate associations are made up of integral troops, not individuals, implying high incremental costs of joining. These costs, plus a paucity of ecologically compatible combinations of species, seem to limit primate polyspecific associations geographically to regions in which the presence of monkey-eating raptors provides a strong incentive for aggregation.