Foraging challenges of red colobus monkeys: influence of nutrients and secondary compounds

The diet selection of two groups of red colobus monkeys (Procolobus badius) in Kibale National Park, Uganda are considered with respect to protein, fiber, digestibility, alkaloids, total phenolics, tannins, saponins, and cyanogenic glycosides. Both groups selected young leaves over mature leaves and young leaves had more protein, were more digestible, and had a higher protein to fiber ratio than mature leaves. Young and mature leaves did not differ with respect to secondary compounds. There were no differences in the phytochemical factors examined between frequently eaten foods and leaves that red colobus were never known to eat, but were relatively common in the environment. Regression analyses predicting foraging effort from the phytochemical components of the large group's diet revealed selection for only one factor, foods that are high in protein and low in fiber, when differences in food tree availability were taken into consideration. A similar analysis with the small group did not suggest selection or avoidance of foods with respect to any of the factors considered. Previous studies have found the biomass of folivorous primates to be related to the ratio of protein to fiber concentration of mature leaves in the environment. These investigations have considered variation in folivore biomass and forest composition among sites separated by hundreds of kilometers; however, large variation in folivore abundance occurs over much smaller spatial scales. In Kibale National Park the average protein to fiber ratio of the mature leaves of the 20 most abundant tree species predicted the biomass of red colobus among four neighboring sites. We examined the generality of this relationship by adding our biomass and leaf chemistry values to previously published values; 62% of the variance in colobine biomass was explained by variation in the protein to fiber ratios of mature leaves at the sites. There was no evidence that red colobus avoided plants with high levels of secondary compounds. In fact, one of the most preferred trees (Prunus africana) was the species with the highest levels of cyanogenic glycosides, and the highest saponin levels were found in the young leaves of Albizia grandibracteata, the sixth and fourth most preferred plant species for the large and small groups, respectively.     

Application of Protein-to-Fiber Ratios to Predict Colobine Abundance on Different Spatial Scales

The biomass of arboreal folivorous primates in Africa and Asia is related to an index of mature leaf quality: the ratio of protein-to-fiber concentration. Investigations have considered variation in folivore biomass and forest composition among sites separated by hundreds or thousands of km. However, large variation in folivore abundance has been documented over much smaller spatial scales. We quantify the degree to which the average protein-to-fiber ratio of mature leaves of the 20 most abundant tree species predicts the biomass of western red colobus (Piliocolobus trephosceles) and black-and-white colobus (Colobus guereza) over very small spatial scales. Four sites within Kibale National Park, Uganda, varied markedly in forest structure. Colobine biomass varied among sites from 191 to 2675 kg/km² and was related to the average protein-to-fiber ratio of mature leaves of the 20 most abundant tree species at each site. We examined the generality of the relationship between protein-to-fiber ratios and colobine abundance by adding our biomass and leaf chemistry values to previously published values to produce 9 comparable sites. At these locations, colobine biomass varied from 84 to 2675 kg/km² (mean biomass among sites = 910 kg/km²), and mean protein/fiber ratios varied from 0.167 to 0.577. Colobine biomass was related to the protein-to-fiber ratios of mature leaves (R ² = 0.616, P = 0.012).     

Implications of small scale variation in ecological conditions for the diet and density of red colobus monkeys

In this 3-year investigation we documented patterns of density, diet, and activity of red colobus monkeys (Procolobus tephrosceles) in six areas in or near Kibale National Park, Uganda and related these patterns to availability of food resources. There were large differences in the density and behavior of the red colobus among the sites. For example, the red colobus at one site with a diverse plant community of more than 61 tree species, had a diet that included at least 42 species. In contrast, at a second site red colobus spent 92% of their feeding time eating from one species that dominated the tree community. The density of important red colobus food trees varied among sites from 32 trees/ha to 204 trees/ha, and red colobus density ranged from 0.70 groups/km² to 7.41 groups/km². Among sites, red colobus density was related to the cumulative DBH of important food trees, when one apparently anomalous site was excluded, and populations with more plant species in their diets tended to be those that were found at higher densities. Activity budgets of the red colobus populations varied markedly among sites. For example, feeding time ranged among sites from 29 to 55%, and traveling varied from 5 to 20%. When faced with increased foraging demands, red colobus reduced the time spent resting, while the time spent socializing remained fairly constant. Comparative socioecological studies typically contrast species separated by large geographical distances to ensure there is sufficient variation in the environment to detect behavioral responses. The marked differences in ecological conditions and red colobus behavior we documented over short geographical distances, suggests that small-scale contrasts are a useful tool to examine ecological determinants of behavior and community structure.     

Constraints on Group Size in Red Colobus and Red-tailed Guenons: Examining the Generality of the Ecological Constraints Model

The ecological constraints model proposes that an increase in group size will increase intragroup feeding competition and thereby constrain group size. Although this model has received wide acceptance, tests of it are based only on a few studies of species that have similar ecological requirements and social organizations, and there are reasons to question the widespread acceptance of the assumptions underpinning it. Via a 2-year study, we explored determinants of group size in species that feed on markedly different types of foods: the folivorous red colobus (Procolobus pennantii) and the frugivorous/insectivorous red-tailed guenon (Cercopithecus ascanius). We established 4 study sites approximately 15 km apart in Kibale National Park, Uganda, to examine the relationship between average group size and food availability. In both species, we quantified interdemic variation in diet, density of food trees, rate of travel, and group size. Red colobus at all sites relied heavily on leaf resources (75.5%–86.9%), but fruit (6.4%–13.9%) and flowers (2.0%–13.9%) were important in some populations. In general, red-tailed guenons fed on fruit (35.7%–59.7%), insects (14.5%–17.6%), and young leaves (12.2%–32.8%), but the amount of time allocated to these foods varied among sites. Average monthly density of trees bearing food items ranged among sites from 45 to 79 trees/ha for red colobus and from 19.6 to 67.3 trees/ha for red-tailed guenons. For both species, rate of travel was similar among sites, with one exception for red colobus. Average red colobus group size varied among sites from 14 to 40 (28 groups counted). Red-tailed guenon group size varied among sites from 11 to 24 (16 groups counted). As predicted by the ecological constraints model, group size increased with food tree density across sites for both species.     

Coping with Forest Fragmentation: The Primates of Kibale National Park,Uganda

A goal of conservation biology is to determine which types of species are most susceptible to habitat disturbance and which types of disturbed habitats can support particular species. We studied 20 forest fragments outside of Kibale National Park, Uganda, to address this question. At each patch, we determined the presence of primate species, tree species composition, patch size, and distance to nearest patch. We collected demographic, behavioral, and dietary data for Abyssinian black-and-white colobus (Colobus guereza). Black-and-white colobus and red-tailed guenons (Cercopithecus ascanius) were in almost all fragments; Pennant's red colobus (Procolobus pennantii) and chimpanzees (Pan troglodytes) were in some fragments; and blue monkeys (Cercopithecus mitis) and gray-cheeked mangabeys (Lophocebus albigena) were absent from all fragments. No species characteristics—home range, body size, group size, or degree of frugivory—predicted the ability of species to live in patches. No characteristics of patches—area, distance to the nearest patch, distance to Kibale, or number of food trees present—predicted the presence of a particular species in a patch, but distance to Kibale may have influenced presence of red colobus. Black-and-white colobus group size was significantly smaller in the forest patches than in the continuous forest of Kibale. For a group of black-and-white colobus in one patch, food plant species and home range size were very different from those of a group within Kibale. However, their activity budget and plant parts eaten were quite similar to those of the Kibale group. The lack of strong predictive variables as well as differences between other studies of fragmentation and ours caution against making generalizations about primate responses to fragmentation.     

Group Size Dynamics over 15+ Years in an African Forest Primate Community

Group size affects many aspects of the ecology and social organization of animals. We investigated group size stability for five primate species in Kibale National Park, Uganda from 1996 to 2011 at three nested spatial scales. Survey data indicated that group sizes did not change for most species, with the exception of red colobus monkeys (Procolobus rufomitratus), in which group size increased at all spatial scales. Mangabey (Lophocebus albigena) group size increased in old‐growth forest, but the sample size and increase were small. To augment this survey data, we collected several years of demographic data on three habituated groups of redtail monkeys (Cercopithecus ascanius), eight groups of black‐and‐white colobus (Colobus guereza), and one red colobus group. The red colobus group increased from 59 to 104 individuals, while redtail monkey and black‐and‐white colobus group sizes were stable, mirroring our survey results. To understand mechanisms behind group size changes in red colobus versus stability in other primates, we monitored forest dynamics at two spatial scales between 1990 and 2013, considered changes in predator population, and explored evidence of disease dynamics. The cumulative size of all trees and red colobus food trees increased over 24 yr, suggesting that changing food availability was driving group size changes for red colobus, while predation and disease played lesser roles. Overall, our results and evidence of changing primate densities suggest that the Kibale primate community is in a non‐equilibrium state. We suggest future conservation and management efforts take this into consideration.     

Predicting folivorous primate abundance: validation of a nutritional model

Understanding the determinants of animal abundance has become more vital as ecologists are increasingly asked to apply their knowledge to the construction of informed management plans. However, there are few general models are available to explain variation in abundance. Some notable exceptions are studies of folivorous primates, in which the protein-to-fiber ratio of foods has been shown to predict biomass. Here we examine the generality of Milton's [American Naturalist 114:363-378, 1979] protein/fiber model by providing a detailed analysis of diet selection in black-and-white colobus monkeys (Colobus guereza), and applying the model to populations shown to be stable; an assumption not previously examined. Based on observations of two groups of black-and-white colobus in Kibale National Park, Uganda, and one group in a forest fragment, we documented that the animals selected young leaves that had more protein, were more digestible, and had a higher protein-to-fiber ratio than mature leaves. The mature leaves did not differ from young leaves with respect to secondary compounds or mineral content (with the exceptions of copper and zinc). All of the colobus groups selected foods with a high protein-to-fiber ratios. However, one group also selected more digestible foods, and in another group, foraging efforts were positively related to zinc and negatively related to potassium. Previous studies that examined Milton's protein/fiber model did not demonstrate that the study populations were stable. If some populations were not at carrying capacity, then the correlations drawn between food availability and/or quality and folivore biomass may have been spurious. To address this issue, we censused a series of forest fragments in 1995 and again in 2000. We found that the populations in these fragments had declined from 165 in 1995 to 119 animals in 2000. However, based on evidence of population stability and lack of forest disturbance, we concluded that five of the original populations were stable. The biomass of these populations was related to the protein-to-fiber ratio of the fragment's trees. Combining our data with published data, we demonstrate that the protein-to-fiber ratios of mature leaves available to these folivorous primates accounted for 87% of the variance in their biomass.     

Mineral Resource Availability and Consumption by Colobus in Kibale National Park,Uganda

Very little information exists on mineral nutrition of tropical, forest-dwelling species, yet minerals are critical to growth, reproduction, and survival. We examined the mineral resources available to and consumed by colobus in Kibale National Park, Uganda. We combined behavioral data on black-and-white (Colobus guereza) and red colobus (Piliocolobus tephrosceles) in a section of unlogged forest, a heavily logged area, and a forest fragment with mineral analysis of their foods to estimate the proportion of the diet containing specific minerals (mineral content). We compared mineral content of colobus foods (natural and crops) across plant parts and among plant species. Additionally, we estimated mineral intake of frugivorous primates in Kibale from published dietary data and our estimates of mineral content of foods. Dietary mineral content for all colobus groups and frugivorous species is similar despite significant differences in the mineral content of foods. Ripe and unripe fruits are lower in mineral content than most foods. Foods rarely consumed, such as bark, petioles, and caterpillars have high levels of some minerals. The mineral content of crops is low in comparison to that ofnatural foods. For all colobus groups of both species, sodium content of foods was extremely low and iron content was generally low, suggesting that intake isbelow suggested requirements, though current suggested iron requirements may overestimate physiological needs. Copper content was marginal and deficient seasonally for most colobus groups. Despite a sodium-limiting environment, only one of 8 colobus groups appeared to select sodium; however, this may be due to a lack of variation in sodium content among plant species and a positive correlation between high plant sodium content and secondary compounds. Despite the lack of selection for sodium by colobines, some behaviors point to a potential sodium deficiency, including urine drinking, consumption of high-sodium swamp plants, and use of mud-puddles.     

Tree leaf chemical characters: selective pressures by folivorous primates and invertebrates

Plants have evolved a variety of chemical means to deter herbivory. Several studies have documented that secondary compounds are strong deterrents to certain herbivores, while others have demonstrated that some herbivores ingest large quantities of these compounds without exhibiting deleterious effects. This inconsistent response suggests that plants have evolved compounds to deter specific herbivores. Based on a study in Kibale National Park, Uganda, we explored how two major groups of herbivores, invertebrates and colobus monkeys, respond to chemical characteristics of leaves: protein, attractive from a nutritional perspective, and alkaloids, saponins and cyanogenic glycosides, which are all plant defences, detering herbivory. The intensity that colobus monkeys fed on leaves of different tree species was determined by observations (1300 h), and invertebrate herbivory was indexed by collecting leaves from 20 species and digitizing tracings to quantifying invertebrate damage. Invertebrate damage to leaves varied among species (1.5–22.5%), but showed no relationship with saponin or protein content, or the presence or absence of alkaloids. Colobine foraging effort did not relate to the saponin and protein of leaf species, nor to the presence or absence of alkaloids. Prunus africana, the only species to test positive for cyanogenic glycosides, was fed on by colobus monkeys for 8.1% of their foraging time, but, as it occurred at low densities, it was the most preferred species. These results can be interpreted in different ways. First, it is possible that inactive compounds are retained because they increase the probability of producing new active compounds. Secondly, the indices used to evaluate compound effects may be inappropriate. For example, monkeys may only be able to tolerate a toxin to a specific threshold in a single feeding session, but our index of foraging effort was averaged over the year. Thirdly, it may be that these compounds play an active role with organisms not considered (e.g. prevent fungal attack). Finally, these compounds may serve some unknown function and selection may operate for that purpose.     

Influence of chimpanzee predation on the red colobus population at Ngogo, Kibale National Park, Uganda

Frequent hunting of red colobus monkeys (Procolobus rufomitratus) takes place at all long-term chimpanzee (Pan troglodytes) study sites where both species are present. Red colobus are the most commonly selected prey of chimpanzees even when other monkey species are more abundant. In particular, the chimpanzee community at Ngogo, Kibale National Park, Uganda, preys heavily on red colobus monkeys: the chimpanzee hunting success rate is extremely high, and chimpanzees kill many individuals per successful hunt. Census data had suggested that the red colobus population is declining and that predation by chimpanzees may be contributing to this decline. In this paper, I address the impact of hunting on the red colobus population at Ngogo. To test the hypothesis that chimpanzee hunting is sustainable, I am using demographic data collected on red colobus monkeys over a period of 3 years, as well as fecundity and mortality data from previous studies of this species. I apply matrix models and vortex analyses using a sensitivity analysis approach to project future population development. Results show that current rates of hunting are not sustainable, but that chimpanzees are neither more “noble”, nor more “savage” than humans are, but that they also hunt to ensure maximum benefit without regard for the consequences for the prey population.     

Group size in folivorous primates: ecological constraints and the possible influence of social factors

The ecological-constraints model assumes that food items occur in depletable patches and proposes that an increase in group size leads to increased day range due to more rapid patch depletion. Smaller groups become advantageous when an increase in travel costs is not repaid by an increase in energy gained or some other fitness advantage. On the other hand, we also know that group size can be influenced by social factors. Here we contrast the diet and group size of red colobus (Procolobus badius) and black-and-white colobus (Colobus guereza) in Kibale National Park, Uganda to consider how ecological and social factors are affecting their group sizes. Subsequently, we examine whether the insights gained from this detailed comparison can provide an understanding of why the social organization and group size of mantled howlers (Alouatta palliata) and black howlers (A. pigra) differ. Two groups of red colobus and two groups of black-and-white colobus were studied over 10 months. Red colobus groups were larger (48 and 24) than black-and-white colobus groups (9 and 6). The two groups of red colobus overlap home ranges with the two groups of black-and-white colobus; 75% and 95% of their home ranges were within red colobuss home range. There was a great deal of similarity in the plant parts eaten by the two species and both species fed primarily on young leaves (red colobus 70%, black-and-white colobus 76%). In terms of the actual species consumed, again there was a great deal of similarity between species. The average dietary overlap among months for the two neighboring groups of red colobus was 37.3%, while the dietary overlap between the red colobus and the black-and-white colobus group that had its home range almost entirely within the home range of the red colobus groups averaged 43.2% among months. If ecological conditions were responsible for the difference in group size between the two colobine species, one would expect the density of food trees to be lower in the home ranges of the black-and-white colobus monkeys, since they have the smaller group size. We found the opposite to be true. Both black-and-white colobus groups had more food trees and the cumulative size of those trees was greater than those in the red colobuss home ranges. We quantify how these differences parallel differences in mantled and black howlers. The average group size for mantled howlers was 12.9 individuals, and for black howlers it was 5.3 individuals. We explore possible social constraints, such as infanticide, that prevent black-and-white colobus and black howlers from living in large groups.This revised version was published online in April 2005 with corrections to the cover date of the issue.     

Species,age and sex differences in type and frequencies of injuries and impairments among four arboreal primate species in Kibale National Park,Uganda

Animals in the wild often have physical impairments that can affect their fitness. The aim of this study was to compare injuries and impairments of four different primate species (black-and-white colobus, red colobus, red-tailed monkeys, and grey-cheeked mangabeys) living in Kibale National Park (Uganda), and estimate the proportion of injured and impaired individuals among the sexes and age classes. The species differed in the proportion of individuals with injuries and impairments, with 16.7% in black-and-white colobus, 23.1% in red colobus, 16.2% in red-tailed monkey and 30.2% in grey-cheeked mangabeys. Species also differed in the types and location on the body of injuries. Adult animals had more injuries than immatures. Males had more injuries than females, in all but red-tailed monkeys. The results are discussed in relation to the literature on aggressive behavior, locomotion, and predation in these species.     

Primate abundance along five transect lines at Ngogo, Kibale National Park, Uganda

Using the line transect methods, I studied the primate density at Ngogo, Kibale National Park, Uganda for 18 months. Comparisons with other studies show that the population of red colobus monkeys (Procolobus rufomitratus) and blue monkeys (Cercopithecus mitis) is declining, whereas the populations of black-and-white colobus (Colobus guereza), red-tailed monkeys (Cercopithecus ascanius), grey-cheeked mangabeys (Lophocebus albigena), baboons (Papio anubis), and chimpanzees (Pan troglodytes) remain constant or slightly increase. In this paper, I compare data on density from this study to data from previous and recent censuses at Ngogo and with data from other sites in the Kibale forest to examine the stability of primate populations. Furthermore, I test the hypothesis that the changes in red colobus and blue monkey density are due to changes in the forest structure and abundance of their most selected feeding trees, and show that changes in forest composition cannot account for changes in their red colobus abundance, but that hunting by chimpanzees provides a reasonable explanation.     

Population Declines of Colobus in Western Uganda and Conservation Value of Forest Fragments

The processes of habitat loss and fragmentation are probably the most important threats to biodiversity. It is critical that we understand the conservation value of fragments, because they may represent opportunities to make important conservation gains, particularly for species whose ranges are not in a protected area. However, our ability to understand the value of fragments for primates is limited by the fact that researchers have conducted many studies in protected areas, which do not represent most fragments, and studies are typically short term. Here we determine the long-term survival probability of red (Procolobus pennantii) and black-and-white colobus (Colobus guereza) inhabiting forest fragments outside of Kibale National Park, Uganda. Local communities use the fragments primarily for subsistence agriculture and fuelwood. We surveyed primate populations 3 times over 8 yr, made a total inventory of all trees 2 times, contrasted behavior of groups inhabiting 1 fragment with groups in the continuous forest, and judged the conservation value of the fragments by quantifying patterns of forest use by local people. Of the 20 fragments surveyed, 16 supported resident populations of colobus in 1995, 2 were cleared in 2000, and an additional 2 fragments were cleared by 2003. In 1995 we counted 165 black-and-white colobus, whereas in 2000 and 2003, we counted 119 and 75 individuals, respectively. Seven fragments supported red colobus in 1995, 11 in 2000, and 9 in 2003. In 2000 we counted 159 red colobus, while in 2003, we saw 145 individuals. For both species, activity patterns in continuous forest were similar to those in a fragment, with the exception that individuals in the fragment rested more. Colobus in the fragment ate more mature leaves than colobus in the continuous forest did. Fragments supported all the fuelwood needs of an average of 32 people who lived immediately adjacent to them, and partially supported families up to 3 farms away (ca. 400 m), representing 576 people. Intensive harvesting for fuelwood occurred when neighboring households engaged in beer brewing (an average of 9.6% of the households), gin distilling (8.8%), or charcoal production (14.5%). Overall, between 2000 and 2003, the average density of trees declined by 14 trees/ha (range = 0–60 trees/ha). If current rates of clearing continue, the probability that the fragments will continue to support colobus populations is low.     

Hunting Behavior of Chimpanzees at Ngogo,Kibale National Park,Uganda

Chimpanzees (Pan troglodytes) prey on a variety of vertebrates, mostly on red colobus (Procolobus spp.) where the two species are sympatric. Variation across population occurs in hunting frequency and success, in whether hunting is cooperative, i.e., payoffs to individual hunters increase with group size, and in the extent to which hunters coordinate their actions in space and time, and in the impact of hunting on red colobus populations. Also, hunting frequency varies over time within populations, for reasons that are unclear. We present new data on hunting by chimpanzees at Ngogo, Kibale National Park, Uganda, and combine them with earlier data (Mitani and Watts, 1999, Am. J. Phys. Anthropol. 109: 439–454) to examine hunting frequency and success, seasonality, and cooperation. The Ngogo community is the largest and has the most males of any known community. Chimpanzees there mostly hunt red colobus and are much more successful and make many more kills per hunt than at other sites; they kill 6–12% of the red colobus population annually. The number of kills and the offtake of meat per hunt increase with the number of hunters, but per capita meat intake is independent of hunting party size; this suggests that cheating occurs in large parties. Some behavioral cooperation occurs. Hunting success and estimated meat intake vary greatly among males, partly due to dominance rank effects. The high overall success rate leads to relatively high average per capita meat intake despite the large number of consumers. The frequency of hunts and of hunting patrols varies positively with the availability of ripe fruit; this is the first quantitative demonstration of a relationship between hunting frequency and the availability of other food, and implies that the chimpanzees hunt most when they can easily meet energy needs from other sources. We provide the first quantitative support for the argument that variation in canopy structure influences decisions to hunt red colobus because hunts are easier where the canopy is broken.     

The diet of the olive colobus monkey,Procolobus verus,in Sierra Leone

Observations of the feeding behavior of wild olive colobus monkeys (Procolobus verus)were made in southern Sierra Leone, West Africa. Most data came from systematically sampling one habituated social group, which inhabited old secondary rain forest on Tiwai Island. Olive colobus at Tiwai were highly selective feeders, obtaining most of their food from a small number of uncommon middle-canopy trees, from the forest understory, and from climbers. Mature leaf blades were largely ignored; young foliage (particularly of climbers) was a year-round dietary staple, while seeds, flowers, and mature leaf petioles were seasonally important. It is argued that this diet results largely from selection for two different attributes of food: high digestibility and physical location. Preferred foods had low fiber and tannin contents, while preferred feeding sites were in thick low growth and climber tangles. P. verusis the smallest extant primate species using a foregut fermentation system. Observations of its diet accord with inferences drawn from dental anatomy, digestive physiology, and considerations of body size.     

Frequency of cyanogenesis in tropical rainforests of far north Queensland, Australia

BACKGROUND AND AIMS: Plant cyanogenesis is the release of toxic cyanide from endogenous cyanide-containing compounds, typically cyanogenic glycosides. Despite a large body of phytochemical, taxonomic and ecological work on cyanogenic species, little is known of their frequency in natural plant communities. This study aimed to investigate the frequency of cyanogenesis in Australian tropical rainforests. Secondary aims were to quantify the cyanogenic glycoside content of tissues, to investigate intra-plant and intra-population variation in cyanogenic glycoside concentration and to appraise the potential chemotaxonomic significance of any findings in relation to the distribution of cyanogenesis in related taxa. METHODS: All species in six 200 m(2) plots at each of five sites across lowland, upland and highland tropical rainforest were screened for cyanogenesis using Feigl-Anger indicator papers. The concentrations of cyanogenic glycosides were accurately determined for all cyanogenic individuals. KEY RESULTS: Over 400 species from 87 plant families were screened. Overall, 18 species (4.5 %) were cyanogenic, accounting for 7.3 % of total stem basal area. Cyanogenesis has not previously been reported for 17 of the 18 species, 13 of which are endemic to Australia. Several species belong to plant families or orders in which cyanogenesis has been little reported, if at all (e.g. Elaeocarpaceae, Myrsinaceae, Araliaceae and Lamiaceae). A number of species contained concentrations of cyanogenic glycosides among the highest ever reported for mature leaves-up to 5.2 mg CN g(-1) d. wt, for example, in leaves of Elaeocarpus sericopetalus. There was significant variation in cyanogenic glycoside concentration within individuals; young leaves and reproductive tissues typically had higher cyanogen content. In addition, there was substantial variation in cyanogenic glycoside content within populations of single species. CONCLUSIONS: This study expands the limited knowledge of the frequency of cyanogenesis in natural plant communities, includes novel reports of cyanogenesis among a range of taxa and characterizes patterns in intra-plant and intra-population variation of cyanogensis.     

Influence of Chimpanzee Predation on Associations Between Red Colobus and Red-tailed Monkeys at Ngogo,Kibale National Park,Uganda

Colobines often associate with cercopithecines at various African sites. Such polyspecific associations presumably have an antipredation function. At Ngogo, Kibale National Park, Uganda, red colobus (Procolobus rufomitratus) spend considerable time in association with red-tailed monkeys (Cercopithecus ascanius), and they are also heavily hunted by chimpanzees (Pan troglodytes). I conducted behavioral observations and playback experiments to test the hypothesis that red colobus and red-tailed monkeys obtain mutual protection and predator-related benefits by associating. Despite high chimpanzee hunting pressure on red colobus and much lower hunting pressure on red-tailed monkeys, red-tailed monkeys initiate, maintain, and terminate the associations. The results suggest that rather than providing red colobus with protection against chimpanzees, the associations occur mostly because they protect red-tailed monkeys against predation by eagles.     

Red colobus as prey: the leaping habits of five sympatric Old World monkeys

This study explored the leaping habits of five sympatric Old World monkeys (Colobus badius, Colobus guereza, Cercopithecus ascanius, Cercopithecus mitis and Cercocebus albigena) in an attempt to determine why chimpanzees prefer to hunt red colobus. We videotaped the leaps of the monkeys for 3 months in Uganda's Kibale National Park. Data were collected on leap preparation time as well as several other variables of the leaps. The leap preparation time of red colobus was found to be about double that of the other species studied. This difference is a likely reason why red colobus represent the preferred prey of chimpanzees. The hypothesis that red colobus spend more time in isolated trees than do other species was not supported.     

How do differences in species and part consumption affect diet nutrient concentrations? A test with red colobus monkeys in Kibale National Park,Uganda

Within a primate species, diet can be highly variable in composition, even at small spatial scales within the same forest, or temporally, suggesting that primates use different plant species and parts to meet similar nutritional needs. To test whether such differences in the plant species and parts that primates eat affects the nutrient concentrations that they obtain, we observed feeding of seven groups of red colobus monkeys ( Procolobus rufomitratus) residing in Kibale National Park, Uganda. The different groups consumed mostly young leaves from many of the same plant species, but spent different amounts of time feeding on them. As protein and fibre are suggested to be important determinants of colobine food choice and abundance, we analysed multiple samples of 47 food species for protein and fibre. Despite the differences in the plant species and parts eaten, the protein and fibre concentrations for the seven red colobus groups were similar. Our results suggest that colobus monkeys eating diets with differing amounts of species and parts may ultimately receive similar concentrations of nutrients.