Frugivore Community Research Articles

Observations at a Ficus Tree in Malagasy Humid Forest1

ABSTRACTAlthough several authors have recognized that Madagascar has a depauperate frugivore community, little quantitative data is available on this issue. In order to start filling this gap, systematic observations were made at a Ficus tree in the eastern humid forest. Information is presented on the vertebrate species that visited the tree, estimates of total fruit production and proportion consumed by frugivores, and the chemical analysis of the fruits.RÉSUMÉBien que de nombreux auteurs aient reconnu la faible importance des communautés frugivores de Madagascar, peu de données quantitatives sont actuellement disponibles sur cet aspect. Afin de pallier à ce manque, des observations systématiques ont été faites sur un Ficus dans la forêt humide de l'est. Les connaissances apportées concernent les espèces de vertébrés qui ont visité l'arbre, des estimations de la production totale de fruits, des proportions consommés par les frugivores, et des analyses chimiques des fruits.

Mousedeer Densities in a Tropical Rainforest: The Impact of Selective Logging

1. The responses of two frugivorous ungulates, Tragulus javanicus klossi (Chasen) and T. napu borneanus (Miller), to mechanized selective logging in northern Borneo were investigated. 2. Densities of Tragulus species were measured in forest logged 2, 5 and 12 years previously, and in primary forest, by line-transect surveying. Environmental variables thought to influence mousedeer densities were measured to examine the causes of any observed variation. 3. Both Tragulus species were less common in logged forest, with the larger T. napu exhibiting the most marked decline. Differences in the density ratio of the two species between primary and logged forest were consistent with predictions related to fasting endurance and body size. 4 Mousedeer densities were shown to be negatively correlated with the proportion of severely disturbed forest, and positively correlated with the availability of potential food resources. Densities of T. javanicus were correlated with the abundance of small fruits, which is consistent with diet records, whilst T. napu densities, and overall mousedeer biomass, were correlated with the density of large strangling Ficus trees. Considered a keystone food resource for many tropical frugivores, this observation emphasizes the importance of Ficus in maintaining frugivore communities and has corresponding implications for forest and conservation management. 5. Mousedeer appear to be more adversely affected by selective logging than other frugivorous ungulates or primates within the same forest. This may reflect limitations in the dietary flexibility of mousedeer imposed by the effects of a small body mass on energetic requirements and digestive capabilities. The need for a highly nutritious and readily digestible diet is assumed to restrict their ability to utilize browse as an alternative to fruit.

Rarity of figs (Ficus) on Madagascar and its relationship to a depauperate frugivore community

Several authors have recognized that Madagascar has a depauperate frugivore community, although few explanations have been offered to explain this observation. In comparison to other tropical Old World forests, Malagasy forest has a reduced diversity and density of Ficus (generally an important keystone group in tropical forests), relatively low fruit productivity, and an unusual phenological sequence. These factors, some of which are presumed to be related to Madagascar’s long isolation from other land masses, are considered important variables to explain the island’s reduced frugivore community.

The role of the white-eyed vireo in the dispersal ofBurserafruit on the Yucatan Peninsula

ABSTRACTWhite-eyed vireos (Vireo griseus) winter in the forests and secondary growth of the Yucatan Peninsula whereBursera simaruba(Burseraceae) is an abundant tree. Twenty-five per cent of all white-eyed vireos observed foraging visitedBurseratrees. In addition, presence and abundance of territorial white-eyed vireos in small forest patches were correlated with the size of theBurseracrop. Vireos were the most reliable dispersers ofBurseraseeds. These birds visited 32 of 35 trees observed for at least three hours. They accounted for approximately half of all bird visits, and two-thirds of the seeds dispersed. Most of the other species rarely visited (<5% of visits) or failed to remove seeds from the tree.Peculiarities of phenology and fruit structure may contribute to the tendency ofBurserato be dispersed by relatively few species. The capsules ofBurserafruits do not open when the fruit ripens; birds apparently locate ripe fruit using visual cues, although these are few. In addition, only a small portion of the crop ripens daily over a 7- or 8-month period. The vireo-Bursera simarubarelationship, found regionally on the Yucatan Peninsula, may result from the prolonged fruit ripening period (October-March), the relatively depauperate frugivore community and the relatively high density of smallBurseratrees in the hurricane-disturbed dry forests.Small trees at all times, and all trees from October to February, depend upon territorial vireos for continuous, highly efficient local dispersal of a small number of fruits. In March and April residual fruits ripen rapidly and synchronously, attracting a greater variety of visitors for broad spectrum dispersal during a period of food scarcity. Thus,Burserahas an unusual two-phase phenological pattern, perhaps alternately to take advantage of both specialized and opportunistic dispersers.

Primate seed dispersal: Coevolution and conservation implications

AbstractEarly studies of primates have demonstrated that many species rely heavily on fruit, and that primates constitute a large component of the frugivore biomass in tropical forests. Consequently, primates have long been thought to be important seed dispersers. It is only recently that studies have been conducted that have illustrated the complex nature of the interactions between fruit‐eating primates and their food trees. Such studies have raised questions as to the causes and conse‐quences of the intriguing differences between primate communities, the importance of other animals in the interactions (such as dung beetles and rodents that secon‐darily disperse seeds), how primate‐plant interactions evolve, and the significance of primates in forest regeneration and conservation. Since subsistence and com‐mercial hunting of primates has heavily impacted frugivore communities, but left the physical structure of the forest relatively unaltered, studies of primate seed dispersal have important implications for the future of forests where seed dispersers have declined or disappeared.

Predation on palm nuts ( Syagrus romanzoffiana) by squirrels ( Sciurus ingrami) in south-east Brazil

Although Terborgh (1986) suggested that palm nuts are a 'keystone plant resource' for frugivore communities in tropical forests, few studies exist on seed ecology of palm fruit crop (Bradford & Smith 1977, Pifiero etal. 1984, Vandermeer et ali. 1979). Janzen (1983) suggested that seed predators have a major impact on the structure of plant communities in tropical forests. Squirrels are regarded as important seed dispersers and seed predators (Glanz et ail. 1982, Janzen 1972) depending on the habitat and the fruit availability. These rodents frequently consume hard nuts and their distribution may be related to the distribution of food sources such as palms (Glanz 1982). This paper investigates the utilization of the fruits of the 'geriva', ySyagrus romnanZoffiana (Cham.) Glassmnan by squirrels in a tropical upland semideciduous forest in south-east Brazil. Field observations were made from August 1988 to May 1990 in the 250 ha Santa Genebra Reserve in Campinas (22? 49' S, 470 07' W), Sao Paulo State, Brazil. The climate of the region is characterized by one dry (April to September) and one rainy (October to March) season; annual rainfall during the study period was 1366 mm. The feeding assemblage that utilizes Sjyagruis fruits in Santa Genebra is composed of squirrels Seiinrus ingrami Thomas, a small species about 34 cm in length (H. Bergallo, unpub.), capuchin monkeys Cebus apella Linne and brown howler monkeys Aloucattafiusca Ihering. &yagrus rotinanzofJiana is a common palmi in semideciduous forests in south-east Brazil (H. F. Leitao-Filho, pers. comm.). The fruit is an ovoid drupe 2.5 cm in diameter, with a soft exocarp and woody endocarp. Individuals of this species produce fruit all the year round, each plant producing two bunches at a timie.

Gorilla diet in the Lopé Reserve, Gabon: : A nutritional analysis.

The results of an analysis of gorilla diet in the Lopé Reserve, Gabon are presented. Samples were assayed for nutrients and plant secondary compounds (total phenols, condensed tannins and alkaloids) in an attempt to explain gorilla food choice. The diet is the most diverse so far analysed for gorillas; it seems to be a balance between sugary fruit, proteinaceous leaves, and relatively fibrous stems. Most fruits and herbaceous stems are succulent, but some drier, fibrous fruit and bark is also consumed. Seeds are another component of the diet, including unripe ones. Fruit, seeds, leaves and bark may all contain very high levels of total phenols and condensed tannins; but all herbaceous stems assayed contain low levels of these compounds. Alkaloids are not apparently a significant component of gorilla foods, and may be avoided. Gorillas at Lopé tend to avoid fatty fruit, and select leaves which are high in protein and low in fibre compared to the general vegetation. When fruit and preferred young leaves are scarce, proteinaceous barks and mature leaves, and sugary pith, are important sources of nutrients. We conclude that gorillas exploit the broad frugivore niche in West African lowland forests, and are part of the frugivore community there. What distinguishes them is their ability to eat large fibrous fruit, mature leaves and stems, and to overcome high levels of phenolics (we use "phenolics" as an umbrella term for both total phenols and condensed tannins). Gorilla diet at Lopé overlaps greatly with that of sympatric, frugivorous, primates, and resembles more closely that of chimpanzees than it does gorilla diet studied elsewhere in Africa.

Trophic structure of a neotropical frugivore community: is there competition between birds and bats?

Dietary overlap and competition between frugivorous birds and bats in the Neotropics have been presumed to be low, but comparative data have been lacking. We determined the diets of volant frugivores in an early successional patch of Costa Rican wet forest over a one month period. Ordination of the diet matrix by Reciprocal Averaging revealed that birds and bats tend to feed on different sets of fruits and that diets differed more among bat species than among bird species. However, there was overlap between Scarlet-rumped Tanagers and three Carollia bat species on fruits of several Piper species which comprised most of the diet of these bats. Day/night exclosure experiments on P. friedrichsthalli treetlets provided evidence that birds deplete the amount of ripe fruit available to bats. These results indicate that distantly related taxa may overlap in diet and compete for fruit, despite the apparent adaptation of animal-dispersed plant species for dispersal by particular animal taxa.