Large-bodied Frugivores Research Articles

Habitat associations of an insular Wallacean avifauna: A multi-scale approach for biodiversity proxies

The endemic avifauna of Wallacea is of high conservation significance, but remains poorly studied. Identifying priority conservation areas requires a greater understanding of the habitat associations of these bird communities, and of how spatial scale of analysis can influence the interpretation of these associations. This study aims to determine which proxy habitat measures, at which spatial scales of analysis, can provide useful inferential data on the composition of Wallacean forest avifauna. Research was conducted within the Lambusango forest reserve, South-East Sulawesi, using point count surveys to sample avifauna. Habitat properties were characterised in three ways: broad classification of forest type, canopy remotely-sensed response derived from satellite imagery, and in situ measures of vegetation composition and structure. Furthermore, we examined avifauna–habitat relationships at three spatial scales: area (c.400ha per sample site), transect (c.10ha) and point (c.0.2ha). Results demonstrate that broad forest type classifications at an area scale can help to determine conservation value, indicating that primary and old secondary forests are important for supporting many species with lower ecological tolerances, such as large-bodied frugivores. At the transect-scale, significant congruence occurs between bird community composition and several habitat variables derived from vegetation sampling and satellite imagery, particularly tree size, undergrowth density, and Normalised Difference Vegetation Index (NDVI) values; this highlights the importance small scale habitat associations can have on determining α-diversity. Analysis at the point-scale was ineffective in providing proxy indications for avifauna. These findings should be considered when determining future priority conservation areas for Wallacean avifauna.

Resurrecting Extinct Interactions with Extant Substitutes

There is increasing evidence that restoration ecologists should be most concerned with restoring species interactions rather than species diversity per se [1]. Rewilding with taxon substitutes, the intentional introduction of exotic species to replace the ecosystem functions of recently extinct species, is one way to reverse ecosystem dysfunction following the loss of species interactions [2]. This is highly controversial [3], in part because of a lack of rigorous scientific studies [4]. Here we present the first empirical evidence of an in situ rewilding project undertaken as a hypothesis-driven ecosystem management option. On Ile aux Aigrettes, a 25-hectare island off Mauritius, the critically endangered large-fruited endemic ebony, Diospyros egrettarum (Ebenaceae), was seed-dispersal limited after the extinction of all native large-bodied frugivores, including giant tortoises. We introduced exotic Aldabra giant tortoises, Aldabrachelys gigantea, to disperse the ebony seeds. Not only did the tortoises ingest the large fruits and disperse substantial numbers of ebony seeds, but tortoise gut passage also improved seed germination, leading to the widespread, successful establishment of new ebony seedlings. Our results demonstrate that the introduction of these exotic frugivores is aiding the recovery of ebonies. We argue for more reversible rewilding experiments to investigate whether extinct species interactions can be restored.

The Long-term Impact of Timber Harvesting on the Resource Base of Chimpanzees in Kibale National Park, Uganda

Commercial timber harvesting results in the loss of critical habitat for tropical forest fauna, and large-bodied frugivores (including chimpanzees and most other apes) may experience particularly detrimental effects. Few quantitative data, however, are available to evaluate the long-term impact of harvesting on chimpanzees and other apes. In particular, few data are available to compare population demographics and/or forest composition before and after timber harvesting at the same site. Utilizing detailed forestry department records of logging operations conducted in the late 1960s, present-day botanical surveys, and long-term data on the feeding ecology of chimpanzees in Kibale National Park (KNP), Uganda, I examined the impact that logging has had on KNP chimpanzee communities of known size and demography. Although some important chimpanzee food resources were harvested in high abundance during commercial logging operations, the overall impact on the most predominant dietary items (those making up roughly 75% of the chimpanzees’ diet) and on presumably critical subsistence resources was limited. Furthermore, the low density of chimpanzees inhabiting the logged region of KNP is apparently not attributable to the impact of logging at the site: comparisons of resource densities at this ‘low-chimpanzee-density’ site with that of an unlogged and ‘high-chimpanzee-density’ KNP site did not differ when logging concessions at the low-chimpanzeedensity site were excluded from the analysis. This study suggests that low-intensity logging can be compatible with the conservation of large-bodied frugivores, provided that dietary data are taken into account in forest management planning.

The role of seed mass on the caching decision by agoutis, Dasyprocta leporina (Rodentia: Agoutidae)

It has been shown that the local extinction of large-bodied frugivores may cause cascading consequences for plant recruitment and overall plant diversity. However, to what extent the resilient mammals can compensate the role of seed dispersal in defaunated sites is poorly understood. Caviomorph rodents, especially Dasyprocta spp., are usually resilient frugivores in hunted forests and their seed caching behavior may be important for many plant species which lack primary dispersers. We compared the effect of the variation in seed mass of six vertebrate-dispersed plant species on the caching decision by the red-rumped agoutis Dasyprocta leporina Linnaeus, 1758 in a land-bridge island of the Atlantic forest, Brazil. We found a strong positive effect of seed mass on seed fate and dispersal distance, but there was a great variation between species. Agoutis never cached seeds smaller than 0.9 g and larger seeds were dispersed for longer distances. Therefore, agoutis can be important seed dispersers of large-seeded species in defaunated forests.

Floristic heterogeneity between forested sites in Kibale National Park, Uganda: insights into the fine‐scale determinants of density in a large‐bodied frugivorous primate

1. Despite a long history of research on the influence of fruit availability on the population density of large-bodied vertebrate frugivores, operational understanding of the factors regulating density in these taxa remains elusive. We propose that fruit resources can be distinguished from one another on the basis of their functional role for the animals in question, and that such a classification system can aid in identifying the most influential determinants of frugivore density. 2. We compared the availability of several resource classes between two sites in Kibale National Park, Uganda separated by only 12 km yet differing threefold in density of chimpanzees (Pan troglodytes). 3. We categorized plant species used for fruit by chimpanzees according to their availability relative to habitat-wide fruit productivity, and by their tendency towards inter-individual fruiting synchrony. We predicted that the site of high chimpanzee density would support a higher density of food plant species tending to produce crops during periods of high habitat-wide productivity [high fruit abundance (HFA foods)] and of those tending to fruit synchronously among individuals during times of low habitat-wide availability (sLFA foods). The first food class should provide chimpanzees with a high nutrient density (and thus promote population growth), whereas the second should provide stable subsistence during lean periods and thus a temporally consistent resource base. 4. Counter to our prediction, only sLFA resources were more abundant at the site of high chimpanzee density than at the site of low density. We suggest that sLFA resources are most important in influencing density of large-bodied frugivores.

Dispersal in a Neotropical tree, Virola flexuosa (Myristicaceae): Does hunting of large vertebrates limit seed removal?

To understand how different frugivores impact dispersal, we studied the assemblage that feed on Virola flexuosa over a two-year period at two sites differing in hunting pressure in Ecuador. We focus on disperser effectiveness and test the hypothesis that seed removal, influenced by differential visits of large-bodied frugivores, will differ between hunted and non-hunted sites. All visiting frugivores were identified, and fruit handling behavior and seed removal rates quantified. Seed traps were placed under fruiting trees to estimate crop size and fruit removal. Seventeen bird and three primate species were recorded foraging in V. flexuosa trees. Toucans and primates were the most important dispersers comprising nearly 85% of visits with six toucan species recorded in 74% of visits. A proportionately larger number of seeds were removed from fruiting trees at a non-hunted site (89.4%) than a hunted site (66.8%). In addition, there were significantly more frugivore visits at the non-hunted than the hunted site. The differences in the frugivore assemblage and the number of seeds dispersed from individual trees between two structurally similar forest sites suggest dispersal limitation resulting from a decline in frugivores.

Effects of frugivore impoverishment and seed predators on the recruitment of a keystone palm

Many plant species are threatened as a result of extinction of their large-bodied frugivores all over the world. Additionally, introduced herbivores and seed predators may cause severe pressure on early stages of plant recruitment. We studied the seed dispersal and seed predation of the keystone palm Euterpe edulis on a land-bridge island with a highly impoverished frugivore fauna and overabundant seed predators, and in a continuous Atlantic forest in Brazil. While the diversity of avian seed dispersers and predators was higher on the mainland, the abundance of seed dispersers was 4-fold higher on the island. Turdus flavipes was responsible for 72% and 96% of seeds removed in the island and mainland, respectively. However, the higher density of T. flaviceps on the island did not result in higher seed removal. In fact, seed removal rate was 1.7 times lower there than on the mainland, probably due to the aggressive behavior of the major seed disperser who defend palm fruits. Seed predation, on the other hand, was markedly higher on the island, where nearly 100% of seeds were preyed upon, but only 0.3% on the mainland. As a consequence of higher seed predation the population of E. edulis has few numbers of seedlings and saplings on the island. Therefore, management of the seed predator populations on the island is a key priority for recovering the natural population of this keystone palm and the frugivores that depend on its fruits.

Effects of habitat fragmentation on bird communities of sand forests in southern Mozambique

We investigated the influence of forest fragment size and isolation on the bird assemblages in the species- and endemic-rich sand forests of the Maputaland Centre of Endemism, southern Mozambique. Point-centre surveys were conducted across 12 sand forest patches that varied in size and isolation. Patch size and isolation had little influence on bird species richness, but the number of individuals decreased significantly with increasing isolation. Furthermore, bird abundances were correlated to a combination of the size and isolation of patches. Many forest specialists, in particular large-bodied frugivores, were highly sensitive to reduced patch size and increased distances between patches. Further fragmentation of the landscape may therefore impair the ability of these forests to support viable populations of forest specialists.

The behavioral ecology and conservation of the orangutan (Pongo pygmaeus): A tale of two islands

Orangutans are the only great apes found outside of Africa. At present, they occur only on the two large Sunda-shelf islands of Sumatra and Borneo. Most researchers recognize two separate subspecies, Pongo pygmaeus abelii in Sumatra and P.p. pygmaeus in Borneo.1,2 Relative to other primates, they have a variety of unusual features. These large-bodied frugivores are among the most solitary of anthropoid primates.3–5 They are also highly dimorphic, with the average body mass (78 kg) of males being more than twice that of females (36 kg).6 Despite its large body size the red ape has more specialized morphological adaptations for arboreality than do the African great apes. Researchers generally recognize sexually mature male orangutans with two physically distinct morphs, a phenomenon described as bimaturism. Males of the relatively smaller morph are known for forcing copulations with adult females.5,7–9.