Mark Leighton

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.

The impact of shifting cultivation on a rainforest landscape in West Kalimantan: spatial and temporal dynamics

To assess the role of shifting cultivation in the loss of rainforests in Indonesia, we examined the spatial and temporal dynamics of traditional land-use north of Gunung Palung National Park in West Kalimantan. We analyzed the abundance, size, frequency, and stature (by tree size) of discrete management units (patches) as a function of land-use category and distance from the village. Data were gathered from point samples along six 1.5-km transects through the landscape surrounding the Dayak village of Kembera. Most land was managed for rice, with 5% in current production, 12% in wet-rice fallows (regenerating swamp forest), and 62% in dry-rice fallows (regenerating upland forest). The proportion of land in dry-rice increased with distance from the village; rubber gardens (17% of the total area), dominated close to the village. The size of rubber trees declined with distance, reflecting the recent establishment of rubber gardens far from the village. Fruit gardens accounted for only 4% of the area. From interviews in Kembera and three other villages, we estimated rates of primary forest clearing and documented changes in land-use. Most rice fields were cleared from secondary forest fallows. However, 17% of dry-rice fields and 9% of wet-rice fields were cleared from primary forest in 1990, resulting in the loss of approximately 12 ha of primary forest per village. Almost all dry-rice fields cleared from primary forest were immediately converted to rubber gardens, as were 39% of all dry-rice fields cleared from fallows. The rate of primary forest conversion increased dramatically from 1990 to 1995, due not to soil degradation or population growth but rather to changes in the socio-economic and political environment faced by shifting cultivators. Although the loss of primary forest is appreciable under shifting cultivation, the impact is less than that of the major alternative land-uses in the region: timber extraction and oil palm plantations.

Tree species distributions across five habitats in a Bornean rain forest

Abstract We examined the distribution of tree species across five habitats in 69 small plots within a single watershed of the Gunung Palung National Park, West Kalimantan, Indonesia (GPNP). The spatially complex distribution and close proximity of habitats provided an opportunity to test habitat specificity of tree species across strong environmental gradients, in a situation where dispersal into ‘inappropriate’ habitat should not be a rare event. Habitat had a weak influence on community structure, although species diversity was lower in the alluvium and peat habitats. Association tests based on two randomization models (spatially independent and explicit) were used to examine habitat distribution of 55 ‘common’ and 142 ‘frequent’ taxa. The general patterns were similar in the two models but the interpretation of specific patterns depended greatly on assumptions about dispersal ability. A majority (67%) of the common species was significantly associated with a single habitat, while few were restricted to one habitat. A small proportion (16%) of the species appear to be habitat generalists. The peat habitat had the most profound effect on species distribution. Overall, a large amount of variation was found in the degree of habitat specificity, even within speciose groups. No obvious evolutionary or ecological correlates with degree of habitat specificity were found. These results suggest that a mixture of stochastic and deterministic processes determine species distribution even across strong environmental gradients. Abbreviations: GPNP = Gunung Palung National Park.; SEMI = spatial dependence; SPI = spatial independence. Nomenclature: Ng (1978, 1989); Soepadmo & Wong (1995); Soepadmo et al. (1996); Whitmore (1972, 1973b).

Forest Fruit Production Is Higher on Sumatra Than on Borneo

Background Various studies have shown that the population densities of a number of forest vertebrates, such as orangutans, are higher on Sumatra than Borneo, and that several species exhibit smaller body sizes on Borneo than Sumatra and mainland Southeast Asia. It has been suggested that differences in forest fruit productivity between the islands can explain these patterns. Here we present a large-scale comparison of forest fruit production between the islands to test this hypothesis. Methodology/Principal Findings Data on fruit production were collated from Sumatran and Bornean sites. At six sites we assessed fruit production in three forest types: riverine, peat swamp and dryland forests. We compared fruit production using time-series models during different periods of overall fruit production and in different tree size classes. We examined overall island differences and differences specifically for fruiting period and tree size class. The results of these analyses indicate that overall the Sumatran forests are more productive than those on Borneo. This difference remains when each of the three forest types (dryland, riverine, and peat) are examined separately. The difference also holds over most tree sizes and fruiting periods. Conclusions/Significance Our results provide strong support for the hypothesis that forest fruit productivity is higher on Sumatra than Borneo. This difference is most likely the result of the overall younger and more volcanic soils on Sumatra than Borneo. These results contribute to our understanding of the determinants of faunal density and the evolution of body size on both islands.

Competition and Niche Overlap Between Gibbons ( Hylobates albibarbis ) and Other Frugivorous Vertebrates in Gunung Palung National Park, West Kalimantan, Indonesia

Interspecific competition is considered to be one of the fundamental forces driving a wide range of evolutionary and ecological processes, but its importance in limiting mammalian populations has been hotly debated (Hairston et al. 1960; Fleming 1979; Schoener 1982; Walter and Paterson 1995). Early ecologists held the view that competition between species was of overriding importance in shaping vertebrate communities (e.g., Grant 1972; MacArthur 1972; Cody 1975; Diamond 1978). Others argued that interspecific competition was sporadic, and that its effects may be relatively unimportant compared to other ecological forces, such as climate or predation (e.g., Connell 1975; Wiens 1977; den Boer 1986; Post and Forschhamer 2002), and non-equilibrial and stochastic factors (e.g. Saether 1997; Hubbell 2001). Despite continued uncertainty over the precise nature of interspecific competition (Schoener 1982; Eccard and Ylonen 2003; Cooper 2004), few ecologists would deny that competition between species can have powerful effects on animal populations. Field experiments have demonstrated that the ecological effects of interspecific competition are widespread (reviewed in Connell 1983; Schoener 1983). Begon, Harper, and Townsend (1996: 800) concluded that competition ‘‘appears frequently to be important in vertebrate communities, particularly those of stable, species rich environments.’’ Most primates live in tropical rainforests, among the most stable and species rich environments on earth, suggesting that interspecific competition may be particularly important for these taxa. Primate field studies have indirectly inferred the importance of interspecific competition, either with primates or other vertebrate species. For example, density compensation—an increase in the density of one species in response to the decline in abundance of a competing species—has been reported in a wide

Enrichment Planting in Selectively Logged Rain Forest: A Combined Ecological and Economic Analysis

We demonstrate how research on innovative agroforestry systems, incor- porating new species and management approaches, can benefit from preliminary financial appraisals that include both economic and ecological variables in quantitative cost-benefit models. Model results provide vital information for planning further research, and thus increase the likelihood of finding practical solutions to urgent resource management prob- lems within reasonable funding and time constraints. As a case study, we evaluate the potential of enrichment plantings of three native fruit-producing genera in selectively logged rain forests of Kalimantan, Indonesia. The models use preliminary estimates of 8 ecological parameters (e.g., survival, growth rate, fruit production) and 11 economic parameters (e.g., planting and harvesting costs, market prices) to predict net present value (NPV) over a variety of project durations and discount rates. Sensitivity analyses examine the effect of changes in input parameters. The genera were chosen (1) for ecological complementarity in the use of light resources and (2) to produce fruit at times when commonly harvested species are unavailable in markets. Dialium spp. are canopy trees that produce timber and a relatively nonperishable fruit; Willughbeia spp. are fast-growing lianas that produce fruit; Garcinia spp. are understory fruit trees. Sensitivity analyses indicate that all three genera have potential for substantial positive NPV, and that NPV projections depend heavily upon fruit price, fruit production, age of first reproduction, juvenile survivorship, and harvesting and marketing costs. In addition, these analyses demonstrate that preliminary, combined ecological-economic analysis can guide the selection of species and research strategies for experimental trials.

Why tropical squirrels carry seeds out of source crowns

The selective pressures affecting whether squirrels remove seeds from source crowns are of interest from the standpoint of seed dispersal and its consequences for plant reproduction. The nature of these forces will affect a plants evolutionary capacity for modifying squirrel behaviour to enhance its reproductive success. Seeds that are dispersed away from the parent tree may have a reduced risk of discovery by predators compared with those dropped beneath the parent crown (Becker & Wong 1985; Janzen 1970; see Clark & Clark 1984 and Howe & Smallwood 1982 for recent reviews of this topic). Here we discuss differences among squirrel species in seed removal from source trees and possible explanations for this behaviour in the hope of inducing others to add to our incomplete, anecdotal observations. We have observed the feeding behaviour of diurnal, arboreal squirrels during an 18-month study in Peninsular Malaysia (Payne 1979), a 24-month study of fruiting and fruit exploitation by vertebrates in East Kalimantan, Indonesian Borneo (Leighton & Leighton 1983), and two weeks of observation on visitors to a fruiting crown of Aglaia sp. (Meliaceae) in Peninsular Malaysia (Becker &

The Great Ape World Heritage Species Project

The mission of the Great Ape World Heritage Species Project is to offer a new way to help avert the extinction crisis that currently faces chimpanzees, bonobos, gorillas, and orangutans, and in so doing to assist the plight of these apes in captivity also. We believe that a higher international profile for the great apes is necessary if they are to survive in the wild. Our goal is therefore to launch a collaboration that will lead to designating the great apes as World Heritage Species. This designation of World Heritage Species would denote a new internationally protected category of species. The essential notion of World Heritage Species status is that any species so named would be recognized to be of outstanding universal value, and to need special help if they are to be conserved in the wild. Outstanding universal value is the operational criterion for nominations to the World Heritage Convention, so designation of World Heritage Species might be through a protocol to this convention. The great apes would be the first set of species to be so named. Others would be expected to follow. We consider that the designation of great apes as World Heritage Species would advance their conservation by accelerating international cooperation in three main ways, signified by attention, resources, and mechanism. Attention means elevating awareness of the value and plight of great apes, particularly among political leaders. Resources means increasing the resources needed to help the great apes, especially by tapping into the worldwide interest in great ape welfare as a result of their unique relationship with humans. Mechanism means creating a new international mechanism for organizing great ape conservation in the wild, given that no such mechanism currently exists. The Great Ape World Heritage Species Project (GAWHSP) was initiated in January 2001 with the appointment by the International Primatological Society of an Ad-hoc Committee for the World Heritage Status for the Great

Conservation Action Plan for Orangutans in Indonesia

The first Population and Habitat Viability Analysis (PHVA) Workshop for Orangutan (Pongo pygmaeus) focused on the status of wild populations of orangutans on Sumatra and Borneo, with major emphasis on the Sumatran population (Pongo pygmaeus abelii). At the Workshop, three working groups were established: Orangutan Distribution and Status in Sumatra, Orangutan Distribution and Status in Borneo, and Life History Characteristics and VORTEX Modelling. Recommendations from these working groups form the basis for the Indonesian Orangutan Action Plan presented here.