Activity and Ranging Patterns of <Emphasis Type="Italic">Colobus angolensis ruwenzorii</Emphasis> in Nyungwe Forest,Rwanda: Possible Costs of Large Group Size

With group sizes sometimes >300 individuals, the Angolan black-and-white colobus (Colobus angolensis ruwenzorii) population in Nyungwe Forest, Rwanda is an intriguing exception to the tendency for folivores to live in smaller groups than expected relative to body size. Researchers have hypothesized that the unusually high quality of foliage at Nyungwe allows colobus there to avoid intragroup feeding competition, releasing constraints on the formation of large groups (Fimbel et al., 2001). We collected data on the activity and ranging patterns of a >300-member Nyungwe colobus group and compared our results to those from smaller groups in other black-and-white colobus (Colobus spp.) populations. Colobus at Nyungwe spent far more time feeding and moving (62%) and far less time resting (32%) than black-and-white colobus at any other site. The annual home range of the Nyungwe colobus was also many times larger (95% minimum convex polygon: 20.7 km ² ; 95% fixed kernel: 24.4 km ² ) than those for other populations. We terminated our research after the group engaged in an unprecedented migration among black-and-white colobus by moving 13 km south of their former range. Our results suggest that intragroup scramble competition may be more intense than originally believed within the large colobus groups at Nyungwe and that long periods of resource renewal may be necessary after a large colobus group passes through an area, thereby potentially helping to explain their wide ranging patterns. We discuss the socioecological convergence between the Nyungwe colobus and Chinese snub-nosed monkeys (Rhinopithecus spp.) and suggest directions for future research on the unique black-and-white colobus population at Nyungwe.

秦岭川金丝猴的一次家庭雄性替代

家庭雄性替代已在亚洲叶猴的许多种类中有所报道。 2 0 0 3年 ,我们在一种亚洲叶猴———秦岭的川金丝猴 (Rhinopithecusroxellana)的一个单雄家庭中观察到一次完整的家庭雄性替代过程。此次替代发生于 4月 2 8日 - 5月 2日的五天时间内。在家庭雄性发生替代后的第六个月 ,该家庭中的婴猴消失。本文是首次对野生川金丝猴家庭雄性替代进行详细的报道。通过本次观察证明野生川金丝猴的确存在家庭雄性替代的现象。且像亚洲叶猴的许多种类一样 ,野生川金丝猴的家庭雄性替代同样发生于产仔季节和交配季节之间。但我们仍无法确定在本次雄性替代中婴猴最终的消失是否是雄性杀婴的结果     

Predation on mammals by the chimpanzee (Pan troglodytes)

With respect to prey selectivity and predation frequency, chimpanzees (Pan troglodytes) show local differences as well as diachronic variability within the same population. When data on predation from three long-term studies at Mahale, Gombe, and Tai are compared, some differences and similarities emerge; Mahale is more like Gombe than Tai in regard of prey selection but features of hunting at Tai with respect to predation frequency are not conspicuous. The most responsible factor for diversity in prey selectivity is a distinct “prey image” maintained by chimpanzees of different populations, although it is necessary to clarify in future studies why and how such tradition develops. Relative body size of chimpanzees to prey species and/or the degree of cooperation among members of a hunting party may explain the variability in prey size selected at each site, the latter influencing the frequency of successful hunts at the same time. Although various degrees of habituation and different sampling methods including artificial feeding might have obscured the real differences, recent data from the three populations do not seem to be biased greatly by such factors. Nevertheless, it is still difficult to make strict comparisons due to the lack of sufficient standardized data across the three populations on the frequency of hunting and predation. It is suggested that the size or demographic trend of a chimpanzee unit-group, especially the number of adult males included, necessarily influences its hunting frequency as well as its prey profile. It is also suggested that factors which bring these males together into a party (e.g. fruit abundance, swollen females, conflict between unit-groups etc.) strongly affect theactual hunting and kill rates. Other possible factors responsible for the local differences are forest structure (e.g. tree height), skilful “hero” chimpanzees, and competition with sympatric carnivorous animals. A total of at least 32 species have been recorded as prey mammals of chimpanzees from 12 study sites and the most common prey mammals are primates (18 species), of which 13 species are forest monkeys. Forest monkeys, colobine species in particular, are often the most common victims of the predation by chimpanzees at each site. We may point out a tendency toward selective hunting for the forest monkeys in terms of the selectivity of prey fauna among all three subspecies of chimpanzees, including populations living in drier environment. The mode of chimpanzee hunting seems to correspond to the highest available biomass of gregarious, arboreal monkeys in the forest, colobine species in particular. In contrast, bonobos (P. paniscus) are less carnivorous than chimpanzees, only rarely preying on a few species of small mammals. The sharp contrast of the two allied species in their predatory tendencies appears to have something to do with the differences in the structure of primary production between their habitats.     

Extinct large colobines from the Plio-Pleistocene of Africa

Three genera and six species of extinct African Plio-Pleistocene Colobinae are discussed. One new genus, Rhinocolobus and three new species, R. turkanaensis, Cercopithecoides kimeui and Paracolobus mutiwa are named. These colobines show a diversity in postcranial and dental morphology not seen among extant species. Rhinocolobus was most similar to extant Colobus in postcranial morphology and had similar high-cusped shearing teeth. Cercopithecoides shows a number of postcranial skeletal features typical of terrestrial cercopithecid species and has lower cusped teeth. Paracolobus, while generally more similar to Rhinocolobus than to Cercopithecoides, is intermediate in some features of its postcranial morphology. The distribution of the various taxa among East and South African sites with different palaeoenvironments is generally consistent with the morphological interpretation. With the exception of Cercopithecoides kimeui, which persisted a little longer, these large colobines disappear from the fossil record about 1.8 million years ago. Their disappearance coincides with an interval of increasing aridity documented at Olduvai Gorge, the Omo Valley, and East Turkana.     

Locomotor response to predator threat in red colobus monkeys

The locomotor patterns of red colobus monkeys (Colobus badius) were scored under three different conditions: normal daily activities, in sight of a terrestrial predator, and after the playback of a crowned hawk-eagle call. Relative to the normal movement activities, the terrestrial and avian predator experiments showed fleeing movements to be very rapid with an increase in the frequency of leaping and vertical bounding. Movement distances also increased in response to the avian playback experiments. Although rare, it is possible that rapid movements may better reflect anatomical design than movements during normal daily activities.     

Miocene fossil cercopithecoids from Kenya

Fossil cercopithecoid material from Ngeringerowa, Ngorora, and Nakali, dated at between 8.5 and 10.5 m.y., is described. The specimens are the only cercopithecoid remains dated between 15 and 6 m.y. from sub-Saharan Africa. The mandible of asmall colobine from Ngeringerowa (similar in size to Colobus verus) is assigned to a new genus and species, Microcolobus tugenensis. Unlike other colobine genera, the symphysis of Microcolobus lacks an inferior transverse torus. A colobine lower M_{1 or 2} from Nakali is longer and narrower than molars of M. tugenensis, indicating that it may belong to a distinct taxon. A P₄ from Ngorora cannot be assigned confidently to subfamily, due to its unique metaconid morphology. The relationship between the new genus and other Miocene monkeys is considered.     

Miocene cercopithecoidea from the Tugen Hills, Kenya

Miocene to Pleistocene fossiliferous sediments in the Tugen Hills span the time period from at least 15.5 Ma to 0.25 Ma, including time periods unknown or little known elsewhere in Africa. Consequently, the Tugen Hills deposits hold the potential to inform us about crucial phylogenetic events in African faunal evolution and about long-term environmental change. Among the specimens collected from this region are a number of discoveries already important to the understanding of primate evolution. Here, we describe additional cercopithecoid material from the Miocene deposits in the Tugen Hills sequence, including those from securely dated sites in the Muruyur Beds (16-13.4 Ma), the Mpesida Beds (7-6.2 Ma) and the Lukeino Formation (∼6.2-5.7 Ma). We also evaluate previously described material from the Ngorora Formation (13-8.8 Ma). Identified taxa include Victoriapithecidae gen. et sp. indet., cf. Parapapio lothagamensis, and at least two colobines. Specimens attributed to cf. Pp. lothagamensis would extend the species’ geographic range beyond its type locality. In addition, we describe specimens sharing derived characters with modern African colobines (Tribe: Colobina), a finding that is congruent with previous molecular estimates of colobine divergence dates. These colobine specimens represent some of the earliest known members of the modern African colobine radiation and, in contrast to previous hypotheses, suggest that early African colobines were mainly arboreal and that semi-terrestrial Late Miocene and Plio-Pleistocene colobine taxa were secondarily derived in their locomotor adaptations.     

Mitochondrial relationships and divergence dates of the African colobines: evidence of Miocene origins for the living colobus monkeys

The African colobines represent a neglected area of cercopithecid systematics. Resolving the phylogenetic relationships and estimating divergence dates among the living forms will provide insight into the evolution of this group and may shed light upon the evolution of other African primates as well. This is the first molecular assessment of the evolutionary relationships among the modern colobus monkeys, which are comprised of the black-and-white, olive, and red colobus groups. Over 4,000 base pairs of mitochondrial DNA were amplified and sequenced in over 40 colobus monkey individuals incorporating representatives from all commonly recognized species. Gene trees were inferred using maximum likelihood and Bayesian inference, and penalized likelihood was employed to estimate mitochondrial divergence dates among the sampled taxa. The results are congruent with some aspects of previous phylogenetic hypotheses based on morphology and vocalizations, although the relationships among several West and Central African taxa differ to some degree. The divergence date analysis suggests that the black-and-white, olive, and red colobus had diverged from one another by the end of the Miocene, and that by the Plio-Pleistocene many of the species lineages were already present. This demonstrates that the initial extant colobus monkey diversification occurred much earlier than previously thought and was likely part of the same adaptive radiation that produced the diverse colobine taxa seen in the African Plio-Pleistocene fossil record. The lack of early members from the modern lineages in fossiliferous deposits suggests that they resided in part in the forests of Central and West Africa, which also currently harbor the highest levels of colobus monkey diversity. These forests should not be ignored in models of Plio-Pleistocene human and nonhuman primate evolution.     

Food selection by the silver leaf monkey,Trachypithecus auratus sondaicus,in relation to plant chemistry

Summary Samples of leaves and fruits exploited as food items byTrachypithecus auratus sondaicus were analysed for nitrogen content, acid detergent fibre (ADF), pepsin cellulase digestibility (CDIG), condensed tannins (CT), total phenolics (TP) and protein precipitation capacity (PP) and compared with fruits and leaves not eaten. Differences in chemical measures for items eaten and not eaten were not statistically significant but trends indicate that leaves may have been selected for their lower fibre content and greater digestibility. Fruits eaten also had a higher mean level of CDIG and lower mean level of ADF than fruits not eaten but these measures are not considered to be of major importance in fruit selection as CDIG was lower and ADF higher in fruits eaten than in leaves eaten. Levels of CT, TP and PP capacity were higher in fruits eaten than in fruits not eaten but lower in leaves eaten than in leaves not eaten. The role of tannins and phenolics in food selection is discussed. Leaves (and fruits) were not strongly selected on the basis of protein content. Approximately half the dietary intake ofT. auratus sondaicus was leaves, a protein-rich food source. Possibly, protein levels in foliage at Pangandaran were sufficient that selection for this nutrient was not required. A nutrient other than protein (for example, soluble carbohydrates) may have been maximised through food selection. The protein/ADF ratio may provide an indicator of the acceptability of foliage in a habitat as potential food for a colobine. However, this ratio did not govern food selection byT. auratus sondaicus at Pangandaran.