Non-fig Fruit Research Articles

Resource partitioning and niche overlap between hoolock gibbon (Hoolock hoolock) and other frugivorous vertebrates in a tropical semi-evergreen forest.

Understanding how niche differences evolve in ecologically similar species and how these differences are maintained is a fundamental question in ecology. We studied resource partitioning and niche overlap between the hoolock gibbon (Hoolock hoolock) and other frugivorous vertebrates from April 2016 to January 2018 in Satchari National Park, Sylhet, Bangladesh. We examined the differences in their diet, niche breadth, niche overlap, and characterization of patch use. We recorded feeding events of gibbons and other frugivorous vertebrates using ad libitum sampling. Gibbons consumed 76 plant species including 32 non-fig fruits and 14 figs. Twenty-one competing frugivorous vertebrate species shared 10-70% of their food species with hoolocks. Competition for fruits was intense among gibbons, macaques, and hornbills, as fruits comprised more than 50% of their diet. The niche breadth of the gibbons varied across seasons. It was lowest during the rainy season (BA = 0.39) when fruits were more readily available, and highest in winter (BA = 0.58) when gibbons were less selective due to food scarcity. The niche overlap was highest between gibbons and northern pig-tailed macaques (Ojk = 0.70), followed by gibbons and hornbills (Ojk = 0.68). Feeding heights and substrate used varied significantly between gibbons and competitors. Gibbons may minimize competition by specializing on various food resources and using different forest patches.

Chimpanzee feeding ecology and fallback food use in the montane forest of Nyungwe National Park, Rwanda.

Almost all primates experience seasonal fluctuations in the availability of key food sources. However, the degree to which this fluctuation impacts foraging behavior varies considerably. Eastern chimpanzees (Pan troglodytes schweinfurthii) in Nyungwe National Park, Rwanda, live in a montane forest environment characterized by lower primary productivity and resource diversity than low-elevation forests. Little is known about chimpanzee feeding ecology in montane forests, and research to date predominantly relies on indirect methods such as fecal analyses. This study is the first to use mostly observational data to examine how seasonal food availability impacts the feeding ecology of montane forest chimpanzees. We examine seasonal changes in chimpanzee diet and fallback foods (FBFs) using instantaneous scan samples and fecal analyses, supported by inspection of feeding remains. Chimpanzee fruit abundance peaked during the major dry season, with a consequent change in chimpanzee diet reflecting the abundance and diversity of key fruit species. Terrestrial herbaceous vegetation was consumed throughout the year and is defined as a "filler" FBF. In contrast to studies conducted in lower-elevation chimpanzee sites, figs (especially Ficus lutea) were preferred resources, flowers were consumed at seasonally high rates and the proportion of non-fig fruits in the diet were relatively low in the current study. These divergences likely result from the comparatively low environmental diversity and productivity in higher-elevation environments.

Feeding Postures of Cao Vit Gibbons (Nomascus nasutus) Living in a Low-Canopy Karst Forest

Food acquisition is an important factor in the evolution of primate postural behavior. Gibbons are well known for their ability to exploit terminal branches by means of below branch suspensory feeding, but few studies of gibbon positional behavior have been conducted since the seminal work of the 1970s and 1980s. We studied the feeding posture of three cao vit gibbon groups living in degraded karst forest in Bangliang Gibbon Nature Reserve between August 2008 and December 2009 to determine if body mass, age, and food type affect feeding posture. We found that cao vit gibbons spent most of their time feeding from branches (59.4 %) and twigs (33.2 %) in the middle canopy of the forest (5–10 m). They used suspensory hanging and sitting as their main feeding postures. Large-bodied gibbons spent more time on larger supports than smaller juveniles when feeding on nonfig fruit and leaves. In addition, gibbons of all age–sex classes adopted a suspensory posture more often when using smaller (twigs) or more flexible (lianas) supports. We found little evidence of age–sex differences in the frequency of suspensory feeding. The subtle differences we did detect suggest that intragroup feeding competition or ontogeny may confound the body size effects on feeding posture. Overall our findings conform to the view that within species positional behavior is largely constrained by musculoskeletal anatomy and not by habitat quality because cao vit gibbons showed a similar pattern of canopy and substrate use to gibbons occupying less disturbed forests.

Fruit resource tracking by hornbill species at multiple scales in a tropical forest in India

Abstract:The fruit-tracking hypothesis predicts a positive association between frugivores and fruit abundance over space and time. We documented hornbill diets and examined the relationship between fruit abundance and abundance of three hornbill species (Buceros bicornis, Rhyticeros undulatus and Aceros nipalensis) in the Eastern Himalaya from 2009–2012. The study was carried out at three scales: at the largest scale of the study area (15 km2), at the intermediate scale – eight 3-ha patches within the study area and at the smallest scale of individual fruiting trees. Ninety-one per cent of the 64 foraging sightings of the great hornbill were on figs while more than 50% of the foraging sightings of the wreathed (83) and rufous-necked hornbills (87) were on non-fig fruits. At the largest scale, wreathed hornbill abundance and ripe fruit abundance peaked in the non-breeding season. At the intermediate scale, wreathed hornbill abundance was positively associated with non-fig fruit availability while rufous-necked hornbill abundance was negatively associated with non-fig fruit availability. At the smallest scale, great and rufous-necked hornbill abundances were correlated with fig and non-fig fruit crop sizes, respectively. The three hornbill species track fruit availability at different scales based on diet, which has implications for their role in seed dispersal.

Socioecological correlates of inter-individual variation in orangutan diets at Ketambe, Sumatra

The diet of great apes consists of several hundred plant species. The factors determining diet differences have been examined between populations but not within a population, probably due to the confounding effect of seasonal fluctuations on fruit availability. In Sumatran orangutans (Pongo abelii), fruit availability appears to be sufficiently high year round to have little influence on diet composition, which in turn allows for addressing this question. We examined the diet of eight adult female orangutans at Ketambe, Sumatra, and investigated whether fig and non-fig fruit availability, association time, and/or home range measures influenced dietary overlap between female dyads. Between most pairs, females’ diets were different: 16 out of 23 pairs had a significantly low diet species overlap. Only fig diet overlap was influenced (negatively) by the availability of non-fig fruit. Association time only influenced (positively) fig diet overlap. Hence, orangutans gathered in fig trees when non-fig fruit availability was low. Home range measures did not influence overall diet overlap. To our knowledge, this is the first study showing that, while controlling for confounding factors, individuals with similar energetic requirements, from the same population and sharing the same area, make different dietary choices relatively to their preferred (non-fig) fruit constituting the majority of their diet. Social transmission, with putative matrilineal diet traditions, suitably explains these results. We discuss the implications of the findings for orangutan conservation, namely on reintroduction and the felling of fig trees.

Seasonal variation of diet and time budget of Eastern hoolock gibbons (Hoolock leuconedys) living in a northern montane forest

Most gibbons dwell in the tropical forests of Southeastern Asia, but eastern hoolock gibbons (Hoolock leuconedys) survive in high montane forest ranging from 1,600 to 2,700m a.s.l. in Gaoligongshan (>24°30'N), Yunnan, China. To assess the behavioral adaptations of hoolock gibbons to the montane forest, we related temperature and food availability within the habitat to the seasonal behavioral patterns of a family group and a solitary female between August 2010 and September 2011 in Nankang, Gaoligongshan National Nature Reserve. The maximum temperature was 29.2°C and the minimum temperature was -0.3°C during the period. The monthly mean temperature was <10°C between December and February, making Nankang the coldest gibbon habitat reported so far. Nonfig fruit and fig availability declined to nearly zero in cold months. The family group increased resting and decreased travel and social behaviors when the monthly mean temperature was low. Compared with other gibbon populations, the hoolock gibbons spent proportionally less time feeding on figs and other fruit than other gibbon populations except Nomascus concolor and Symphalangus syndactylus. Only 36 species of plants provided nonfig fruit or figs, which is less than the number of fruit species consumed by any other gibbon population observed during a similar period of time (about 1year). Hoolock gibbons shifted their diet to leaves and increased feeding time when fruit was not available. We conclude that diet flexibility and an energy-conserving strategy during the cold season when fruit is scarce have enabled the hoolock gibbons to survive in a northern montane forest.

Diet of chimpanzees (Pan troglodytes schweinfurthii) at Ngogo, Kibale National Park, Uganda, 2. temporal variation and fallback foods

Highly frugivorous primates like chimpanzees (Pan trogolodytes) must contend with temporal variation in food abundance and quality by tracking fruit crops and relying more on alternative foods, some of them fallbacks, when fruit is scarce. We used behavioral data from 122 months between 1995 and 2009 plus 12 years of phenology records to investigate temporal dietary variation and use of fallback foods by chimpanzees at Ngogo, Kibale National Park, Uganda. Fruit, including figs, comprised most of the diet. Fruit and fig availability varied seasonally, but the exact timing of fruit production and the amount of fruit produced varied extensively from year to year, both overall and within and among species. Feeding time devoted to all major fruit and fig species was positively associated with availability, reinforcing the argument that chimpanzees are ripe fruit specialists. Feeding time devoted to figs-particularly Ficus mucuso (the top food)--varied inversely with the abundance of nonfig fruits and with foraging effort devoted to such fruit. However, figs contributed much of the diet for most of the year and are best seen as staples available most of the time and eaten in proportion to availability. Leaves also contributed much of the diet and served as fallbacks when nonfig fruits were scarce. In contrast to the nearby Kanywara study site in Kibale, pith and stems contributed little of the diet and were not fallbacks. Fruit seasons (periods of at least 2 months when nonfig fruits account for at least 40% of feeding time; Gilby & Wrangham., Behavioral Ecology and Sociobiology 61:1771-1779, 2007) were more common at Ngogo than Kanyawara, consistent with an earlier report that fruit availability varies less at Ngogo [Chapman et al., African Journal of Ecology 35:287-302, 1997]. F. mucuso is absent at Kanyawara; its high density at Ngogo, combined with lower variation in fruit availability, probably helps to explain why chimpanzee population density is much higher at Ngogo.

A Direct Comparison of Scan and Focal Sampling Methods for Measuring Wild Chimpanzee Feeding Behaviour

Focal sampling is the most accurate method for measuring primate activity budgets but is sometimes impractical. An alternative is scan sampling, in which the behaviour of the group is recorded at regular intervals. The simplest technique is to record whether at least 1 animal is engaged in the behaviour of interest. By direct comparison with focal data collected simultaneously on the same population, we assess the validity of this simple group level sampling method for studying chimpanzee (Pan troglodytes schweinfurthii) feeding behaviour. In a 13-month study at Kanyawara, Kibale National Park, Uganda, group level scan sampling provided statistically similar measures of broad diet composition to those produced by focal data, despite considerable seasonal variation. Monthly means of the percentage of time spent consuming non-fig fruit calculated from group level scan sampling were highly correlated with those from focal sampling. This validates previous methodology used to identify periods of high energy availability. However, group level scans tended to overestimate the percentage of observation time spent feeding, particularly for adult males. We conclude that this method of group level scan sampling provides valuable data for characterizing broad diet choice in chimpanzees and other species, but may be of limited use for estimating individual feeding time.

Flowers Are an important food for small apes in southern Sumatra

Flowers are included in the diets of many primates, but are not generally regarded as making an important contribution to primate energy budgets. However, observations of a number of lemur, platyrrhine, and cercopithecine populations suggest that some flower species may function as key primate fallback foods in periods of low abundance of preferred foods (generally ripe fruits), and that flowers may be preferred foods in some cases. I report heavy reliance on flowers during some study months for a siamang (Symphalangus syndactylus) population in southern Sumatra. Siamangs at Way Canguk spent 12% of feeding time eating flowers from October 2000 to August 2002, and in 1 month flower-feeding time exceeded 40% of total feeding time. The overall availabilities of fig and nonfig fruits, flowers, and new leaves in the study area were not significant predictors of the proportion of time that siamangs spent consuming any plant part. However, flower-feeding time was highest in months when nonfig fruit-feeding time was lowest, and a switch from heavy reliance on fruit to substantial flower consumption was associated with a shift in activity patterns toward reduced energy expenditure, which is consistent with the interpretation that flowers may function as a fallback food for Way Canguk siamangs. Hydnocarpus gracilis, a plant from which siamangs only consume flowers, was the third-most-commonly consumed plant at Way Canguk (after Ficus spp. and Dracontomelon dao), and flowers from this plant were available in most months. It is possible that relatively high local availability of these important siamang plant foods is one factor promoting high siamang density in the study area.

The influence of gibbon primary seed shadows on post-dispersal seed fate in a lowland dipterocarp forest in Central Borneo

The natural seed shadow created by gibbons (Hylobates mulleri×agilis) in Central Kalimantan, Indonesia, was monitored over 11 mo to discern the role of gibbons and post-dispersal events in the spatial pattern of seed germination. Variability in the content and distribution of 183 scats was used to determine which, if any, scat characteristics influenced seed fate. Nine scat characters were evaluated: (1) seed number; (2) number of seed species per scat; (3) scat weight; (4) seed load; (5) rainfall; (6) scat density; (7) distance to nearest fruiting tree; (8) ripe fig abundance; (9) non-fig fruit abundance. More than 99% of monitored seeds were killed, removed, or had germinated during the monitoring period. Vertebrates killed or removed most seeds (86%) and the probability of them moving seeds was highly dependent on non-fig fruit abundance at the time of deposition; factors (2), (6) and (7) also influenced seed removal/predation by vertebrates, depending on whether seeds were deposited in peak or non-peak times of consumption. Insect predation (2% of seeds) occurred mainly in scats that were deposited in months of high ripe fig abundance, while the actual chance of a seed germinating (11% of seeds) was influenced by non-fig fruit abundance at time of deposition and number of species in the original scat. The gibbon-generated seed shadow was profoundly altered by post-dispersal events and variation in the characteristics of the shadow had little lasting impact on the probability of seeds germinating.

Foraging characteristics of an assemblage of four Sumatran hornbill species

This study examines the diets of four hornbill species (Bushy-crested Hornbill Anorrhinus galeritus, Wreathed Hornbill Aceros undulatus, Rhinoceros Hornbill Buceros rhinoceros and Helmeted Hornbill Buceros vigil) common within our 9 km2 study area in the Bukit Barisan Selatan National Park, Sumatra, Indonesia. Line transects and opportunistic sampling were used over one year to collect feeding data, including the tree species and strata in which birds fed, diet items, fruit characteristics and tree crop size. Hornbills fed on 64 species. Figs, non-fig fruits and animals comprised 23.4% (n = 15 species) 51.6% (n = 33 species) and 25% (n = 16 species) of the diet, respectively. Although there was overlap among the diets of the four species, only B. rhinoceros and B. vigil had a statistically significant overlap, primarily due to high fig consumption by both species. B. vigil fed almost exclusively on figs (98.6% of the diet) and a small proportion of animals (1.4%) while 23.1% of the B. rhinoceros diet comprised non-fig fruits and animals (23.1%), with 76.9% figs. A. galeritus and A. undulatus had distinct diets with drupaceous, oily fruits comprising 66.7% and 64.4% of the diets, respectively. We found no significant relationship between the numbers of hornbills visiting fruiting trees and the characteristics of the fruit (weight, length and width). However, maximum crop sizes of diet species significantly influenced the number of feeding hornbills. Hornbill species also differed in the strata in which they fed. A. galeritus and B. rhinoceros were seen in the middle of the canopy 56% and 50.8% of the time, respectively while A. undulatus and B. vigil were observed more frequently in the upper canopy (50% and 74.3% of the time, respectively). The lower part of the canopy was used infrequently by all species. This study suggests that the four hornbill species in our study partition food resources by food type and/or feeding location.

Foraging Patterns of Sympatric Hornbills during the Nonbreeding Season in Arunachal Pradesh, Northeast India1

The diet and food resource partitioning of three sympatric hornbills (Great Hornbill Buceros bicornis, Wreathed Hornbill Aceros undulatus, and Oriental Pied Hornbill Anthracoceros albirostris) during the nonbreeding season were studied relative to fruit availability in a foothill semievergreen forest of Arunachal Pradesh, northeast India. Hornbills fed on fruits of 49 plant species that comprised over 95 percent of their diet. Hornbill species partitioned food resources by varying the relative contribution of figs and non-fig fruits in the diet. Similarity in non-fig fruit diet was low. Ten species contributed to over 90 percent of the non-fig diet. The availability of non-fig fruits was much lower in the nonbreeding season than in the breeding season; however, despite lower fruit availability during the nonbreeding season, hornbills had a wide diet breadth and indirect evidence suggests that Wreathed Hornbills foraged widely in this season for fruit. Great Hornbills relied more on figs that were available year-round. The diverse diet breadth that included rare and patchy fruit resources underscores the importance of conserving large forest tracts for hornbills.

Influence of Forest Seasonality on Gibbon Food Choice in the Rain Forests of Barito Ulu, Central Kalimantan

We describe the diet of two hybrid gibbon groups (Hylobates mulleri x H. agilis) in relation to forest seasonality. We collected data over 12 mo in lowland dipterocarp forest in the Barito Ulu research area, Central Kalimantan, Indonesia. Although non-fig fruit was the main dietary item (52–64% of diet), gibbon diet was most strongly influenced by the availability of flowers. During periods when flowers were most abundant and the gibbons increased consumption of them, they also ate figs or young leaves more often. We suggest that although flowers are nutritionally rich sources of food, providing relatively high levels of protein compared to fruit, they are unlikely to satiate gibbon hunger and they seek dietary bulk from figs or young leaves, because they are easily obtained. Rainfall also influenced food choice, and non-fig fruit availability had a weak influence on fruit selection for one group. The group concentrated feeding on the fruit of a few species when fruit was most abundant and ate a greater diversity of species when fruit was scarce. Gibbon diet appeared not to be influenced by changes in availability of figs, young leaves and diversity of fruiting species.

Seasonality and Socioecology: The Importance of Variation in Fruit Abundance to Bonobo Sociality

The assumption that nonseasonal, evergreen, rain forests contain more continuously available food resources than seasonal rain forests is fundamental to comparisons made between the socioecology of the male-bonded Pan troglodytes and the female-based social system of the Pan paniscus. Chimpanzee females may be less social due to the high costs of feeding competition, whereas in the more food-rich central African rain forests such as the Lomako forest, female bonobos can associate and socially bond. The Lomako Forest experiences two wet and two dry seasons a year. Data on fruit abundance and sociality show that despite monthly variation in fruit availability, there was no consistent seasonal variation in fruit abundance or dietary breadth. Bonobo use of nonfig fruits, figs, THV, and leaves did not follow seasonal patterns. Leaves and THV may act as complementary sources of plant protein and their use was inversely correlated. Monthly variation in fruit abundance was associated with a significant decrease in the number of males in a party but not in the number of females. Focal males were frequently solitary during 1 of the 3 months with the smallest party sizes. In contrast, females remained social with each other throughout the year. Therefore, seaonality at Lomako appeared to be less marked than at comparable chimpanzee sites, such that the variation in fruit abundance did not fall below a level that prohibits female sociality.

Modeling dietary selectivity by Bornean orangutans: Evidence for integration of multiple criteria in fruit selection

Food patch visitation was compared to the availability of fruit patches of different species during 2 years in a Bornean lowland forest to examine orangutan (Pongo pygmaeus) diet selectivity. Feeding on both the pulp and the seeds of nonfig fruit varied directly with fruit patch availability, demonstrating preference for these foods over fig fruit or other plant parts (bark or leaves). Factors determining fruit selectivity rank were examined through multiple regression analysis. Modeling selectivity for 52 chemically unprotected “primate-fruit” pulp species revealed strong preferences for species of (i) large crop size (numbers of fruits ripening in an individual patch), (ii) high pulp weight/fruit, and (iii) high pulp mass per swallowed unit of pulp + seed, demonstrating orangutan sensitivity especially to patch size (g of pulp or total energy/patch) and perhaps to fruit handling time. Modeling selectivity for 18 fig species showed that 4 factors significantly influenced fig species rank: crop size, pulp weight/fruit, and 2 chemical variables, percentage digestible carbohydrate and percentage phenolic compounds in the fig fruit pulp. The selectivity rank based on the overall nutrient gain from feeding in the fruit patch (the product of the first 3 variables) is proportionally depressed by the percentage tannin content, demonstrating that orangutans integrate values for these variables in selecting fig patches. The conclusions from these results and from analysis of selectivity for seeds and for other fruit types are that orangutan foraging decisions are strongly influenced by the meal size expected from a feeding visit (i.e., by patch size), that tannins and other toxins deter feeding, and that the energy content, rather than the protein content, of foods is important in diet selection. The foraging strategy of orangutans is interpreted relative to these results and to Bornean fruiting phenology. By integrating spatial, morphometric, and chemical variables in analysis, this study is the first to demonstrate the application of foraging theory to separate out the key variables that determine diet selection in a primate. Multivariate analysis should routinely be applied to such data to distinguish among the many covarying attributes of food items and patches; inferences drawn in previous studies of primate diet selection, which ignore key spatial and morphological variables and rely on univariate correlations, are therefore suspect.

Ecological constraints on the grouping of wild orang-utans (Pongo pygmaeus) in the Gunung Leuser National Park, Sumatra, Indonesia

The orang-utan (Pongo pygmaeus)is an interesting subject on which to base an evaluation of the costs and benefits of social life in apes, since grouping in this heavy, arboreal frugivore is facultative. In the Ketambe area of Sumatra, Indonesia, the food sources of wild orang-utans display a clear seasonality. The two main food types— figs and other, nonfig, fruits— fulfill different functions. The huge fig trees meet the high caloric requirements of the ape and are therefore visited regularly throughout the year. Nonfig fruits are an additional food source but become a really important alternative when figs are in short supply. Since fig trees are relatively rare, it is only in the nonfig fruiting season that food is relatively abundant. Two types of orang-utan groupings could be distinguished. During lean periods, groups formed in the few productive fig trees available can be explained as forced aggregations taking place in spite of centrifugal forces caused by competition. Only when a temporary surfeit of food slackens these centrifugal forces (i.e., during the fruit season) does the tendency to form spontaneous social groups (the second type of grouping) reveal itself. It is suggested that the development of social skills is an important aspect of grouping in adolescent orang-utans. For the adult male, safeguarding his reproductive success by protecting females against sexually aggressive subadult males is probably the only reason for being in groups.