Seasonality in fruit availability affects frugivorous primate biomass and species richness

We examine the effect of total annual food abundance and seasonal availability on the biomass and species richness for frugivorous primates on three continents (n=16 sites) by data on fruit fall. We reveal that the best‐fit models for predicting primate biomass include total annual fruit fall (positive), seasonality (negative) and biogeography (Old World>New World and mainland>island) and that these factors explain 56–67% of the variation. For the number of species, the best‐fit models include seasonality (negative) and biogeography (Old World>New World and mainland>island) but not total annual fruit fall. Annual temperature has additional effects on primate biomass when the effects of fruits and biogeography are controlled, but there is no such effect on species richness. The present results indicate that, measured on local scales, primate biomass and number of species is affected by the seasonal variation in food availability.     

Ecological correlates of abundance in the Tana mangabey (Cercocebus galeritus)

I investigated the ecological correlates of abundance in the Tana mangabey (Cercocebus galeritus), one of the world's most endangered primates, with the goal of recommending management strategies. I systematically selected 31 forest fragments throughout the mangabey's 60-km distribution along the lower Tana River in southeastern Kenya. Within the 31 fragments, I measured vegetation structure, food abundance, and human forest product use in 107 belt transects, and conducted 370 mangabey surveys. I used a weighted multiple regression analysis to determine whether there was a dependence between the selected forest attributes and the mean number of mangabey groups per fragment. Fragment area and density of trees > or =10 cm diameter at breast height (DBH) were the only variables that significantly correlated with the variation in mangabey abundance. No additional variables were significant when the analysis was limited to forest fragments inside the Tana River Primate National Reserve (TRPNR) or to fragments outside the TRPNR. When I estimated the resources available before recent human forest product use by adding nonharvested and harvested variables, the total basal area of the top 15 food species became significant. This was only within the TRPNR, however. Management, therefore, should focus on increasing forest area, density of trees > or =10 cm DBH, and coverage of food trees throughout the mangabey's distribution. Solutions must be found for the problem of forest clearing, and forest product use must be better managed to protect the habitat of this critically endangered primate. The significance of food abundance only within the TRPNR suggests a need to collect dietary data from mangabey groups in fragments toward the southern limit of the mangabey's distribution, where plant species composition differs from that in fragments in which dietary data have been previously collected.     

Environmental effects on Neotropical liana species richness

Aim Lianas differ physiologically from trees, and therefore their species‐richness patterns and potential climate‐change responses might also differ. However, multivariate assessments of spatial patterns in liana species richness and their controls are lacking. Our aim in this paper is to identify the environmental factors that best explain the variation in liana species richness within tropical forests. Location Lowland and montane Neotropical forests. Methods We quantified the contributions of environmental variables and liana and tree‐and‐shrub abundance to the species richness of lianas, trees and shrubs ≥ 2.5 cm in diameter using a subset of 65 standardized (0.1 ha) plots from 57 Neotropical sites from a global dataset collected by the late Alwyn Gentry. We used both regression and structural equation modelling to account for the effects of environmental variables (climate, soil and disturbance) and liana density on liana species richness, and we compared the species‐richness patterns of lianas with those of trees and shrubs. Results We found that, after accounting for liana density, dry‐season length was the dominant predictor of liana species richness. In addition, liana species richness was also related to stand‐level wood density (a proxy for disturbance) in lowland forests, a pattern that has not hitherto been shown across such a large study region. Liana species richness had a weak association with soil properties, but the effect of soil may be obscured by the strong correlation between soil properties and climate. The diversity patterns of lianas and of trees and shrubs were congruent: wetter forests had a greater species richness of all woody plants. Main conclusions The primary association of both liana and tree‐and‐shrub species richness with water availability suggests that, if parts of the Neotropics become drier as a result of climate change, substantial declines in the species richness of woody plants at the stand level may be anticipated.     

Tree population dynamics in Kibale National Park, Uganda 1975–1998

Changes in species composition, stem abundance, and basal area of trees taller than or equal to 10 m in a medium altitude tropical rain forest at the Ngogo study area, Kibale National Park, Uganda are described for the period between 1975 and 1998 ( n  = 23 years). Two enumeration episodes were conducted in 263 plots of 5 m by 50 m during 1975–80 and 1997–98. During this period, species richness decreased by 3% (from 92 to 89). Species diversity (H') also declined slightly from 2.97 to 2.86. The number of trees recorded in the sample plots decreased by 8% (from 2545 to 2329), while basal area decreased from 49.48 m² ha⁻¹ to 48.68 m² ha^−1. However, stem abundance and basal area increased for some species.     

Primate Group Size and Abundance in the Caatinga Dry Forest, Northeastern Brazil

The Caatinga dry forest poses a series of ecological challenges for mammals in general and primates in particular. The erratic rainfall pattern impacts on plant diversity and phenological patterns; from year to year there is marked variability in fruit production and failure to fruit is common. The harshness apparently accounts for the impoverished mammalian fauna. However, data on primate abundance, distribution, and possible environmental effects on primate density are lacking in this type of dry forest. I censused the primate community in 3 habitats of the Serra da Capivara National Park, Piaui, NE Brazil, over a total distance of 318 km. Overall, the abundance of primates in the Caatinga dry forest is very low as a consequence of low abundance of food resources both in space and time. Alouatta caraya (predominantly folivorous) occurs at extremely low density, and during the dry season are apparently confined to canyon areas, where trees retain their leaves. Callithrix jacchus has morphological feeding specializations for gum-eating, and gum is an important resource during food bottleneck periods. Nonetheless, Callithrix jacchus occurs at comparatively low densities. Group sizes for howlers and marmosets in the Caatinga are significantly smaller than in other forest types. Contrarily, Cebus apella libidinosus had an average group size within the range reported for Amazonian and Atlantic forests. Researchers consider the generalized diet of capuchins as the explanation for their similar abundance in different habitats, indicating relative independence from ecological constraints. However, I suggest that capuchin foraging style and cognitive abilities are important factors accounting for their unreduced group size and density even under extreme conditions.     

Diurnal primate densities and biomass in the Kakamega Forest: an evaluation of census methods and a comparison with other forests

Line-transect surveys were conducted at the Isecheno study site in the Kakamega Forest, western Kenya to estimate diurnal primate densities. The estimates from several different methods of analysis of census data were compared to "true" density values based on home range size and overlap for two species. The Whitesides method [Whitesides et al., 1988], which incorporates species-specific mean group spread into its formula for estimating transect width, provided the most accurate density estimates. The importance of including as many groups as possible when calculating density from home range size and overlap is demonstrated with long-term data from Colobus guereza and Cercopithecus mitis. Colobus guereza group density at Isecheno was much lower than that published from a recent brief study [von Hippel, 1996]. Cercopithecus mitis group density has fallen while overall population biomass appears to have remained stable over 20 years of study. Isecheno has the second highest diurnal primate biomass of the ten Guineo-Congolian rainforest sites for which biomass data are available, despite having the lowest primate species richness. Within the Guineo-Congolian rainforest system, primate biomass appears to vary to some extent between ecogeographic regions: two of three mid-elevation East African sites have high biomasses, two of two lowland West African sites have intermediate biomasses, and four of five lowland Central African sites have low biomasses. There is a strong positive correlation between total colobine biomass and total primate biomass at the ten Guineo-Congolian rainforest sites.     

Primate assemblage structure in Amazonian flooded and unflooded forests

There is considerable variation in primate species richness across neotropical forest sites, and the richest assemblages are found in western Amazonia. Forest type is an important determinant of the patterns of platyrrhine primate diversity, abundance, and biomass. Here we present data on the assemblage structure of primates in adjacent unflooded (terra firme) and seasonally inundated (várzea and igapó) forests in the lower Purús region of central-western Brazilian Amazonia. A line-transect census of 2,026 km in terra firme, 2,309 km in várzea, and 277 km in igapó was conducted. Twelve primate species were recorded from 2,059 primate group sightings. Although terra firme was found to be consistently more species-rich than várzea, the aggregate primate density in terra firme forest was considerably lower than that in the species-poor várzea. Consequently, the total biomass estimate was much higher in várzea compared to either terra firme or igapó forest. Brown capuchin monkeys (Cebus apella) were the most abundant species in terra firme, but were outnumbered by squirrel monkeys (Saimiri cf. ustus) in the várzea. The results suggest that floodplain forest is a crucial complement to terra firme in terms of primate conservation in Amazonian forests.     

Responses of Primates to Landscape Change in Amazonian Land‐bridge islands—a Multi‐scale Analysis

Large hydroelectric dams are one of the current drivers of habitat loss across Amazonian forests. We investigated how the primate community at a hydroelectric dam in Brazilian Amazonia responded to changes in the landscape and local habitat structure of land‐bridge islands after 21 yr of post‐isolation history. The Balbina Dam, constructed in 1986, inundated 3129 km² of primary forests and created more than 3500 variable‐sized islands. We conducted primate and habitat structure surveys on 20 islands from 5 to 1815 ha, and extracted forest patch and landscape metrics for each island. The number of primate species per island varied between 0 and 7 species. Primate composition varied substantially according to both island area and forest cover remaining within the landscape, whereas island area alone was the most significant predictor of richness. Locally, tree density and vertical stratification were the most significant explanatory variables of primate composition and richness. A model containing area effects had the most explanatory power regarding site occupancy for most species. Individually, each species responded differently, with howler and brown capuchin monkeys showing greater tolerance to cope with habitat changes. Body size was also an important predictor of primate occupancy. We recommend protecting large fragments and enhancing the suitability of surrounding habitats to ensure primate conservation in most Neotropical fragmented landscapes. Given the flat topography of hydroelectric reservoirs, which mainly favors the formation of small islands, and the escalating hydropower development plans in Amazonia, our findings provide evidence for pervasive detrimental impacts of dams on primate communities.     

Liana community and functional trait analysis in tropical dry evergreen forest of India

Aim Lianas are abundant and diverse throughout the world and constitute an important structural and functional component of tropical forests. This study aims to investigate liana diversity, abundance and their functional traits in Indian tropical dry evergreen forest (TDEF).Methods A total of ten 1-ha plots, one each in 10 Indian TDEF sites were demarcated. Each 1-ha plot was divided into one-hundred 10- × 10-m quadrats to facilitate woody species inventory. All lianas ≥1cm diameter measured at 130cm from the rooting point and all trees ≥10-cm girth at breast height (gbh) were recorded from the study sites to analyze the patterns of liana diversity and abundance and also to compare the contribution of lianas to the total woody species richness, density and basal area. Liana variables across the study sites were compared using one-way analysis of variance. The qualitative functional traits of inventoried lianas and trees were assessed on the field and referring to pertinent field manuals.Important findings A total of 9237 liana individuals (ranged from 408–1658 individuals ha^-1) representing 52 species, 45 genera and 28 families were encountered from the 10 study sites. Liana species richness ranged from 11–31 species ha^-1 in 10 sites, which averaged 23.4 (±5.7) species ha^-1. The total basal area of lianas in the study sites was 7. 3 m 2 (0.20–1.76 m 2 ha^-1). There was a significant variation in liana species richness, density and basal area across the studied sites. On the whole, lianas contributed 52%, 49.3% and 4.1% to the total woody species (lianas and trees) richness, density and basal area, respectively. Liana trait analysis revealed the majority (50%) of lianas belonged to brevi-deciduous type. Stem twining was the chief climbing mechanism, exhibited by 21 species (52.6% of total abundance). More than half of the liana species (34 species; 6925 individuals) had microphyllous leaves. Fleshy-fruited lianas mostly bearing berries and drupes constituted the major fruit type in the studied sites. Zoochory was the predominant dispersal mode observed in 63.4% of species. Considering the ecological and functional role of lianas in Indian TDEF, the need for conservation is emphasized.     

The Effect of Spatial Structure of Pasture Tree Cover on Avian Frugivores in Eastern Amazonia

The movement of frugivores between remnant forests and successional areas is vital for tropical forest tree species to colonize successional habitats. The response of these species to the spatial structure of pasture tree cover is largely unknown. We studied avian frugivores that were found in primary forest edges and large pastures in eastern Amazonia, Brazil. We determined how the small‐scale spatial structure of pasture trees at forest edges affects five response variables: bird presence, visitation rate, duration of visit, species richness, and an index accounting for species’ level of frugivory and abundance in forests. We used hierarchical linear models to estimate the effect of four predictor variables on response variables: (1) clustering of pasture trees; (2) percent canopy cover of pasture trees; (3) distance of pasture tree to forest edge; and (4) tree crown area. The study species, many of which are widely distributed in the Neotropics, were generally insensitive to percent cover and clustering of trees. Frugivore visitation to individual trees remained constant as cover increased. Visitation was positively correlated with focal tree distance to forest edge and crown area. The positive relationship between distance and visitation rates may be due to the increased abundance of some resource further from forests. If pastures were abandoned the distance from forest edges would not likely limit frugivore visitation and seed deposition under large pasture trees in our study (i.e., up to 200 m distant).     

Implications of shifts in coffee production on tree species richness, composition and structure on small farms around Mount Kenya

Small coffee farms around Mount Kenya in Kenya contain many planted and remnant tree species but little is known in the region about the relationship between trees on farms and the methods and dynamics of coffee production. Shifts in production may alter tree diversity and potentially impact on future biodiversity conservation efforts by affecting niches available for indigenous trees on farms. Here, knowledge was gathered on how changes in coffee production on 180 small farms around Mount Kenya may affect tree diversity, categorizing farms according to coffee yield levels over a period of five years as increasing, decreasing or stable production. Tree species richness, abundance and composition were analyzed using species accumulation curves, Rènyi diversity profiles, rank abundance and ecological distance ordinations, and the effects of coffee production examined using quasi-Poisson generalized linear regressions. Species richness were positively correlated with tree basal area but negatively related to coffee, banana and maize yields value. A difference in average tree species richness, abundance and basal area on increasing farms was observed compared to the decreasing and stable farms, even though formal tests on richness and densities differences were inconclusive. These dynamics do not significantly influence vegetation structure but seem to have a bearing on species composition on farms of different coffee production. The overall low abundance (23 % of trees) but high richness (78 % of species) of indigenous trees on coffee farms could change markedly if the dynamics observed in the current study persist, indicating the need for the development of intensified multi-species cropping systems.     

Fruit biomass availability along a forest cover gradient

Habitat loss is the main driver of the current high rate of species extinction, particularly in tropical forests. Understanding the factors associated with biodiversity loss, such as the extinction of species interactions and ecological functions, is an urgent priority. Here, our aim was to evaluate how landscape‐scale forest cover influences fruit biomass comparing different tree functional groups. We sampled 20 forest fragments located within landscapes with forest cover ranging from 2 to 93 percent in the Atlantic forest of southern Bahia, Brazil. In each fragment, we established five plots of 25 × 4 m and carried out phenological observations on fleshy fruit throughout 1 year on all trees ≥5 cm dbh. We estimated fruit availability by direct counting of all fruits and derived fruit biomass from this count. We used spatial mixed linear models to evaluate the effects of forest cover on species richness, abundance, and fruit biomass. Our results indicated that forest cover was the main explanatory variable and negatively influenced the total richness and abundance of zoochoric and shade‐tolerant but not shade‐intolerant species. A linear model best explained variations in richness and abundance of total and shade‐tolerant species. We also found that forest cover was positively correlated with the fruit biomass produced by all species and by the shade‐tolerant assemblages, with linear models best explaining both relationships. The loss of shade‐tolerant species and the lower fruit production in fragments with lower landscape‐scale forest cover may have implications for the maintenance of frugivore, seed dispersal service, and plant recruitment.     

Vegetative predictors of primate abundance: utility and limitations of a fine-scale analysis

Determining ecological predictors of primate abundance is important for both theoretical and applied conservation management. For forest primates, research has focused on comparisons of primate abundance and vegetation in different forest blocks or forest compartments with different management histories. However, great variation in primate abundance often occurs within single forests, especially in mountainous areas or in areas with habitat mosaics due to past disturbance. Here we assess, for the first time, the usefulness and limitations of small-scale, within-transect analysis of vegetative parameters as predictors of primate abundance in a very heterogeneous forest habitat in the Udzungwa Mountains of Tanzania. Relative abundance of four species of diurnal primates was recorded over a period of 2.5 years by walking three census transects 48 times each. Tree size, density, species composition, and food plants were measured along the same census lines. The fine-scale relationship between primate abundance and vegetative variables was analyzed through generalized linear modeling applied to 58 segments of these three census lines. Each segment was 200 m in length. For all four primate species, we found significant associations between their abundance and selected vegetative variables. The abundance of the endemic and endangered Udzungwa red colobus Procolobus gordonorum was positively related to mean basal area of large trees (diameter at breast height greater than 20 cm) and to the species richness of their food plants. Considering the very great variation in primate abundance that was recorded among segments of the census lines, our approach proved useful in predicting the relationship between primate abundance and small-scale habitat differences. The main limitation of this study, however, was the relatively low-predictive power of the models for some species, especially the Angolan colobus Colobus angolensis. We discuss the potential reasons for this problem and suggest possible improvements for future studies.     

Forest community survey and the structural characteristics of forests in China

Most of the world’s terrestrial biome types can be found in China. To systematically investigate species composition and structure of China’s forest communities, we launched a long‐term project consisting forest vegetation surveys across China’s mountains in the mid 1990s. Over the study period, we have conducted vegetation surveys for 65 mountains and collected vegetation data from about 1500 forest plots, using consistent sampling protocols. In this paper we first introduce the aims, protocols, and major research themes of the project, and then describe the major characteristics of forest communities and their geographic patterns and climatic controls. As latitude increased, diameter at breast height (DBH) and height of trees increased, while individual density of trees and woody species richness decreased. Total basal area (TBA) of trees and species richness of herbs did not vary with latitude. Contemporary climate seems to drive these patterns: temperature was the leading factor for DBH, precipitation was most important for tree height and individual density, actual evapotranspiration (a surrogate of productivity) determined woody (trees and shrubs) species richness, and rainfall was the major controller of the herb species richness. The species–abundance relationship showed that species dominance (measured by the number of individuals per species) declined significantly from boreal forests to evergreen broadleaf forests from north to south. Our results are in line with the idea that productivity drives woody species richness. Similarly, we find that biomass (measured as TBA) is invariant along the environmental gradients. However, individual density varies dramatically, in contrast to the assumptions underlying the metabolic theory of ecology.     

Asian Primate Species Richness Correlates with Rainfall

Previous studies of meta-analyses found significantly positive correlations between primate species richness and rainfall for Africa, Madagascar and the Neotropics, with the exception of Asia, leaving the open question whether that anomaly is the result of sampling bias, biogeography, or some other factor. This study re-examines the question using modelled data, with primate species richness data from the Southeast Asian Mammals Databank and rainfall data from the Climatic Research Unit. Data processing with Geographical Information Systems resulted in 390 sample points. Reduced major axis and ordinary least squares regressions were employed to examine the relationship for six regions, including the whole study area of Southeast Asia, and the subareas of Huxley West, Huxley East, Mainland Southeast Asia, Borneo, and Sumatra. The results showed a significant positive relationship between primate species richness and mean annual rainfall for Southeast Asia (r = 0.26, P<0.001). Comparing the results for the large islands and Mainland Southeast Asia showed that Sumatra had the highest correlation (r = 0.58; P<0.05). After controlling for the major biogeographic effect associated with Huxley’s Line, our results showed that primate species richness is positively associated with mean annual rainfall in Southeast Asia. Our findings contrast to prior studies of meta-analyses that showed no relationship between rainfall and primate species richness in Asia, and thereby bring Asia into agreement with results showing significant positive correlations between rainfall and primate species richness everywhere else in the world. The inference is that previous anomalous results for Asia were result of sampling bias in the meta-analysis.     

Beyond species area curves: application of a scale‐free measure for spatial variability of species richness

We report a novel pattern in species richness, complementary to the well‐known species–area relationship. We show that, as sample area increases, the variation in relative richness decreases among otherwise comparable spatial units. This pattern holds for southern African birds, French birds, Cape Proteaceae and the trees of Barro Colorado Island. We propose a scale‐free method for quantifying this pattern by measuring the multifractal intensity of species richness, which is the multi‐scale tendency of adjacent patches with the same area to differ in richness. By this measure, spatial variability is strongest for Cape Proteaceae and weakest for Barro Colorado Island trees. Our results have implications for area‐dependent estimates of species‐richness, for example in reserve planning and in simulation‐based studies. They imply that such estimates are most accurate for large areas, and will be subject to substantial uncertainty when the multifractal intensity is high and the area is small. For comparative purposes, multifractal intensity may be used as a supplement or as an alternative to mean richness, as well as for other ecological densities, such as biomass distribution and local abundance.     

Effects of population density on forest structure and species richness and diversity of trees in Kampong Thom Province, Cambodia

This study examined differences in stand structure, tree species richness, and tree species diversity in relation to population density in Kampong Thom Province, Cambodia. Tree data were obtained from a 1997 forest inventory involving 60 clusters (540 plots) systematically distributed over 30% of the provincial forest area. Spatially referenced population data were obtained from the 1998 national population census. The average number of trees per cluster was 356/ha, the average basal area, 23 m²/ha, the average stand volume, 217 m³/ha, and the average aboveground biomass, 273 Mg/ha for all trees of DBH 10 cm and larger. The average species richness per cluster was 37 species, while average species diversity was measured as 0.916 using Simpson’s index and 2.98 by Shannon’s index. Significant negative correlations were generally found between population density surrounding clusters and tree density, basal area, stand volume, aboveground biomass, and species richness and diversity for three examined diameter classes (DBH of 10–30, ≥30, and ≥10 cm). As the distance from clusters for calculating population density increased, the correlation levels increased up to 5 or 7 km, depending on the variables and diameter class, and then stayed relatively constant for stand structure variables and decreased for species richness and diversity. The results indicate that evidence of disturbance was more pronounced at higher population density up to around 5 to 7 km. We suggest that introduction of greater controls on human disturbance should be a high priority for resource management and conservation in Kampong Thom Province and, presumably, Cambodia as a whole.     

Native tree regeneration in native tree plantations: understanding the contribution of Araucaria angustifolia to biodiversity conservation in the threatened Atlantic Forest in Argentina

Deforestation is a global process that has strongly affected the Atlantic Forest in South America, which has been recognised as a threatened biodiversity hotspot. An important proportion of deforested areas were converted to forest plantations. Araucaria angustifolia is a native tree to the Atlantic Forest, which has been largely exploited for wood production and is currently cultivated in commercial plantations. An important question is to what extent such native tree plantations can be managed to reduce biodiversity loss in a highly diverse and vulnerable forest region . We evaluated the effect of stand age, stand basal area, as a measure of stand density, and time since last logging on the density and richness of native tree regeneration in planted araucaria stands that were successively logged over 60 years, as well as the differences between successional groups in the response of plant density to stand variables. We also compared native tree species richness in planted araucaria stands to neighbouring native forest. Species richness was 71 in the planted stands (27 ha sampled) and 82 in native forest (18 ha sampled) which approximate the range of variation in species richness found in the native forests of the study area. The total abundance and species richness of native trees increased with stand age and time since last logging, but ecological groups differed in their response to such variables. Early secondary trees increased in abundance with stand age 3–8 times faster than climax or late secondary trees. Thus, the change in species composition is expected to continue for a long term. The difference in species richness between native forest and planted stands might be mainly explained by the difference in plant density. Therefore, species richness in plantations can contribute to local native tree diversity if practices that increase native tree density are implemented.     

林分密度对杉木人工林林下植被和土壤性质的影响

以杉木人工林为研究对象,探究4种林分密度（A：650株/hm²;B：1100株/hm²;C：1250株/hm²;CK：1650株/hm²）林下物种多样性、生物量以及土壤理化性质及其之间的相关性。结果表明：（1）灌木层Shannon-Wiener指数、Patrick丰富度指数及草本层中Shannon-Wiener指数、Simpson指数、Patrick丰富度指数随林分密度的增加均呈现出双峰型变化趋势,在密度A和C处均出现峰值;灌木层Simpson指数、Pielou均匀度指数随林分密度升高而降低,且灌、草层4种多样性指数最小值均出现在密度CK处。（2）草本层生物量比灌木层高。草本层总生物量（地上+地下）随密度的增大而减少,凋落物的量则随密度的增大而增大。（3）土壤养分含量和林下植物多样性指数随林分密度增大的变化趋势大致相同,且有机质含量在密度A取得最大值。（4）灌木层Shannon-Wiener指数、Patrick丰富度指数与全氮、水解氮、有效磷、有机质呈显著正相关;草本层植被物种多样性与土壤理化性质无显著相关性。（5）各指数与灌木层生物量的相关性较强。综上所述,密度A （650株/hm²）能够促进杉木林林下植被发育,增加林下植被物种多样性、生物量和有机质,可提升维持地力的能力,有利于杉木林稳定持续发展。     

Measuring fruit patch size for three sympatric indonesian primate species

Food availability is one of the basic factors affecting primate density and socioecology, but food availability is difficult to assess. Two different ways to obtain accurate estimates of food availability have been proposed: using phenology data or using the behaviour of animals. Phenology data can be refined by only including trees that are large enough to be used; including (potential) tree species in which by the concerned primate species forage; or including (fruiting) trees of these species that actually produce fruit. Alternatively, the sizes of the actually visited trees (foraging trees) give an estimate of fruit availability. These measures are compared for three sympatric primate species at the Ketambe Research Station, Sumatra, Indonesia: the Thomas langur, the long-tailed macaque and the orangutan. The sizes of fruiting trees and the foraging trees are larger than the potential trees. The sizes of the potential trees and of the fruiting trees are similar for the three primate species. This, however, is not reflected in the use of trees: the langurs forage on average in trees of similar size to those producing fruit, whereas the macaques and orangutans forage in trees larger than those producing fruit. The use of trees does not necessitate a different cut off point of included dbhs for the three compared primate species. The use of trees of different sizes, however, may be regulated by food competition. This indicates that sympatric primates make different foraging decisions and that behavioural measures of food availability will be less reliable.