Kim R. McConkey

Selection of Fruit by Gibbons (Hylobates muelleri£ agilis) in the Rain Forests of Central Borneo

Gibbons (Hylobates spp.) are among the main frugivorous primates in Southeast Asia, yet little is known about the criteria by which they select fruit for consumption. We studied two gibbon groups for 14 mo in the lowland dipterocarp forests of Central Borneo to determine their selectivity for different fruit species and traits. Ideal gibbon fruit were yellow, large, with a juicy-soft pulp, thin skin and available in large crops. Gibbons ultimately sought seedless fruit, but when seeds were present they selected fruit with a single, well-protected seed. Given that few fruit exhibited all the desired traits, we also carried out a multiple regression using the selection ratios of the various fruit species and their associated fruit traits to determine which traits ultimately determined gibbon choice. The analysis was stratified to account for differences in fruit availability. Selection was strongest when fruit were abundant in the forest and was based on seed width (<21 mm), color (yellow-orange), and fruit weight (1–5 g). No selection is apparent when food abundance was intermediate, but when fruit were scarce they preferentially ate larger fruit (6–30 g).

Primary Seed Shadow Generated by Gibbons in the Rain Forests of Barito Ulu, Central Borneo

Gibbons are one of the main frugivores in the forests of Southeast Asia, and consequently have long been considered to be good seed dispersers. This is the first study in which the primary seed shadow they create by their ranging and foraging activities is evaluated in detail. I studied two gibbon groups over 12 months in lowland dipterocarp forest in central Borneo. The gibbons dispersed up to 81% of the species they consumed and destroyed the seeds of only 12%. Fruit with elongated seeds (up to 20 mm wide) were more likely to be dispersed than round seeds. Considering that the survival rate of seeds in the forest to one year was 8%, the gibbons effectively dispersed 13 seedlings ha–1 group–1 year–1. Their effect on germination was very variable, although most species did eventually germinate. Most seeds were deposited along their major ranging routes and close to or under feeding trees. Am. J. Primatol. 52:13–29, 2000.

Husking stations provide evidence of seed predation by introduced rodents in Tongan rain forests

Abstract The islands of Tonga, in Western Polynesia, lacked rodents prior to human colonization. During the past 3000 years, people have introduced three species of rats ( Rattus ). Seed predation by rodents structures plant communities in many parts of the world. Therefore, there is the potential for rats to have a significant impact on the regeneration of plant communities in Tonga. We found 53 husking stations—sheltered sites used by rats to strip inedible protective structures (husks) from the seeds they eat—on eight islands in Tonga. The stations contained 13,555 empty husks from at least 18 plant species, but only 165 viable seeds and seedlings. These husking stations provide evidence of seed predation by rats. Determining the extent to which seed predation threatens plant regeneration will be important for conservation of native forest remnants.

Influence of gibbon ranging patterns on seed dispersal distance and deposition site in a Bornean forest

Frugivores display daily and seasonal behavioural variation, yet the influence of this variability on subsequent seed shadows is rarely considered. We investigated the extent to which three aspects of gibbon ( Hylobates muelleri × agilis ) foraging and ranging behaviour (revisitation of favoured fruit sources, daily and monthly ranging patterns) influenced seed dispersal distances and deposition sites for two groups in dipterocarp forests at the Barito Ulu research site, Kalimantan, Indonesia. Dispersal distances and sites were estimated using gut retention times and ranging patterns collected over 12 mo. Gibbons dispersed few seeds (0.7%) under parent trees and most seeds (> 90%) were dispersed more than 100 m. Mean dispersal distances differed significantly between groups (339 m and 431 m) and across different months. Deposition site was only influenced by time of day, with all seeds swallowed in the first hour of activity being deposited under sleeping trees used that night. Both groups visited all 0.25-ha quadrats within their home range over the study period, indicating that gibbons potentially disperse seeds throughout their home range. Given the general uniformity of the gibbon seed shadow, the intensity of home range use and large seed dispersal distances, gibbons appear to be consistently effective seed dispersers and are probably one of the most important frugivores in Asian rain forests.

Seed dispersal by Pacific Pigeons (Ducula pacifica) in Tonga, Western Polynesia

Abstract Owing to extensive prehistoric extinctions of large frugivores, Pacific Pigeons (Ducula pacifica) are thought to be one of the most important seed dispersers of large-seeded plants in Tonga, yet little is known about their interactions with their food plants. We reviewed their known food plants and recorded defaecations, regurgitations, and movement patterns of this species over 11 months in Tonga. The fruit of at least 38 native plant species and the leaf buds of one species are eaten by Pacific Pigeons in Tonga. Most defaecations and all regurgitations contained a single seed of a single species. Pigeons usually regurgitated seeds larger than 20 mm in diameter whereas smaller seeds were typically defaecated. On the basis of observed movement patterns in Tonga and retention times for Ducula, most seeds are probably dispersed away from fruiting trees (85% of regurgitated seeds, 99% of defaecated seeds), but within 50 m of the crown. Distances of more than 100 km are theoretically possible for defaecated seeds, although pigeon behaviour is likely to limit this maximum. Results from this study suggest Pacific Pigeons are excellent seed dispersers in Tonga.

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.

Low mammal and hornbill abundance in the forests of Barito Ulu, Central Kalimantan, Indonesia

Faunal surveys in Kalimantan have been biased towards primates in protected forests close to the coast. Relatively little has been documented on other animal species, particularly in the vast interior forests. The results of a 1996–97 census of nine large mammal and eight hornbill species in tropical lowland forest in Barito Ulu, Central Kalimantan are reported here. Pigs Sus barbatus had the highest biomass, but this was due to large numbers migrating through the study area over 4 months and the resident population is probably low. Langurs Presbytis rubicunda and hybrid gibbons Hylobates mulleri × agilis had the highest biomass of all resident species. Orang-utans Pongo pygmaeus were absent from the area during the study period and pig-tailed macaques Macaca nemestrina were rarely seen. The resident hornbill species ( Anthracoceros malayanus, Anorrhinus galeritus, Buceros vigil and B. rhinoceros ) had high densities compared to that reported from lowland areas, but overall hornbill density was low due to the absence of the nomadic Aceros corrugatus and A. undulatus , except during peak fruit abundance. Sun bears Helarctos malayanus , long-tailed macaques M. fascicularis , muntjacs Muntiacus spp. and mouse deer Tragulus spp. were at low densities. Density of two large squirrel species, Ratufa affinis and Sundasciurus hippiurus , was lower than has been reported in Sarawak, but the density of Prevosts squirrel Callosciurus prevostii was higher. We discuss hunting pressure, isolation, low abundance of large fruit trees, poor soils, and specific habitat preferences as possible explanations for the low mammal and hornbill density at Barito Ulu.

Seed dispersal by the sun bear Helarctos malayanus in Central Borneo

Bears (Ursidae) are well known consumers of fruits and play an important role as seed dispersers in temperate forests (Welch et al. 1997, Willson 1993 and references therein). For tropical forest-dwelling bear species, however, very little information is known about frugivory and seed dispersal (Young 1990). The sun bear Helarctos malayanus is the smallest of the living bears, weighing from 24 to 65 kg (Ward & Kynaston 1995) and occurring throughout most of South-east Asia (Payne et al. 1985, Ward & Kynaston 1995). Their diet is described as bees nests (honey), termites, small animals and fruits (Payne et al. 1985). Ridley (1930) suggested that sun bears can disperse seeds of durians (Durio zibethinus, Bombacaceae), but nothing else had been reported on their role as seed dispersers. Here we report observations on the frugivory and seed dispersal by the sun bear in Central Kalimantan, Indonesia. The observations were carried out at the Barito Ulu Research Area (hereafter Rekut Camp), a 430-ha forest located in Central Kalimantan, Indonesia, at the confluence of the Rekut and Busang Rivers (113°56′E, 0.6°S). The vegetation is tropical hill evergreen rain forest with a dominance of Dipterocarpaceae (Whitmore 1984). The soils are acidic and low in nutrients

The Seed Dispersal Niche of Gibbons in Bornean Dipterocarp Forests

Most tropical rain forest plants are adapted to have their seeds dispersed by animals (Richards 1996). A profusion of birds, mammals, insects, and occasionally reptiles and amphibians consume fruits, but they differ in their ranging behavior, ability to manipulate seeds, and, hence, their seed dispersal effectiveness (van der Pijl 1982; Corlett 1998). It was assumed for many years that effective seed dispersers had close coevolutionary relationships with their selected fruit species (McKey 1980), but more recent research indicates that coevolution has generally been on a diffuse scale – between suites of dispersers and fruits (Herrera 1985). The development of close relationships are hindered by the diversity of frugivores that feed on most plant species [only rarely is a plant species dispersed by a single species (e.g., Cochrane 2003)] and by inconsistencies in frugivore foraging over time or space (Chapman and Chapman 2002), or even within a single fruiting season of a plant species [e.g., small sources may attract a different array of frugivores than large sources (Russo 2003)]. Furthermore, very few dispersed seeds produce a reproductive, adult plant with subsequent life stages overriding any subtle advantages of one dispersal mode over another (Howe andMitiri 2004). For a frugivorous species to develop amore direct coevolutionary relationship with favored plant species, it must have a clearly defined niche in the frugivore community, providing a consistent and unique dispersal service that can have a lasting positive impact on the survival and establishment of dispersed seeds. Effective seed dispersers should disperse many seeds (quantitative component), from multiple sources, and in a manner that maximizes the survival and subsequent germination of the seeds (qualitative component) (Schupp 1993). One of the most important aspects of seed dispersal is the removal of seeds away from the canopy of the parent plant, where there are often higher rates of seed

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.