Evaluating the suitability of planted forests for African forest monkeys: a case study from Kakamega forest, Kenya

As natural forest cover declines, planted forests have come to occupy an increasing percentage of the earth's surface, yet we know little about their suitability as alternative habitat for wildlife. Although some primate species use planted forests, few studies have compared primate populations in natural and nearby planted forests. From March 2006 to July 2010, we conducted line transect surveys and assessed group sizes and compositions in natural and nearby 60-70 year old mixed indigenous planted forest to determine the densities of diurnal primate species (Colobus guereza, Cercopithecus mitis, C. ascanius) in these two forest types at Isecheno, Kakamega Forest, Kenya. Line transect data were analyzed using the Encounter Rate, Whitesides, and Distance sampling methods, which all provided broadly consistent results. We found that all three diurnal primate species occupy both natural and planted forest at Isecheno. However, group densities of the two Cercopithecus species were 42-46% lower in planted than in natural forest. Colobus guereza achieved comparable group densities in the two forest types, although the species is found in smaller groups, and thus at lower (35%) individual density, in planted than in natural forest. Following a logging episode in the planted forest mid-way through our study, Cercopithecus ascanius group densities fell by 60% while C. mitis and Colobus guereza group densities remained stable over the next two years. Overall, our results suggest that while primate species vary in their response to habitat disturbance, planted forest has the potential to contribute to the conservation of some African monkey species. Even for the relatively flexible taxa in our study, however, 60-70 year old mixed indigenous planted forest failed to support densities comparable to those in nearby natural forest. From the perspective of Kakamega's primates, planted forests may supplement natural forest, but are not an adequate replacement for it.     

A note on the present situation of the primate fauna found from south-eastern Cameroon to northern Congo

Brief results of a survey are reported for the primate fauna in south-eastern Cameroon and northern Congo. The survey was carried over the period from October 1988 to January 1989. I confirmed the occurrence ofMandrillus sphinx in the south-eastern part of Cameroon, viz. the south bank of the Dja river, the occurrence ofCercocebus albigena in almost all the survey areas, the occurrence ofCercopithecus cephus, C. nictitans, C. pogonias, andGorilla g. gorilla throughout the areas, and the occurrence ofCercopithecus neglectus andColobus badius near Bomassa, 70 km north of Ouesso, in Congo. I also confirmedColobus polykomos satanas in some parts of Cameroon, but this species is declining. Local people provided information onCercocebus galeritus agilis, Colobus guereza, andPan troglodytes in almost all the areas, in some of which I confirmed the animals directly. They also provided information aboutCercocebus torquatus on the north bank of the Dja river in Cameroon andMiopithecus talapoin in Sembe in Congo, although I could not confirm these species myself. Human activities had begun reducing the populations of the above primates, particularly those ofMandrillus sphinx, Colobus polykomos satanas, andGorilla g. gorilla, in south-eastern Cameroon and in northern Congo despite the low density of the human populations.     

Positional behavior in five sympatric old world monkeys

Observations of positional behavior and habitat use were recorded on focal individuals of five species of Old World monkeys at Kibale Forest, Uganda, through the dry season of 1990 and 1991. Cercopithecus ascanius, Cercopithecus mitis, Cercocebus albigena, Colobus badius, and Colobus guereza commonly utilize five similar types of positional behavior (i.e., quadrupedalism, leaping, climbing, sitting, and standing), but in varying frequencies and situations. As a group, colobines use oblique supports and leap more often, and cover greater linear distances during leaps than do cercopithecines. Colobines also prefer to sit (about 90% of all postures), while cercopithecines stand more frequently. Body size differences between the sexes of a species are not reflected in positional behavior. The two small-bodied species climb more and leap less often than the three larger species, which is the reverse of what we would expect. Leaping is the most common method of crossing open spaces within the canopy; but most spatial gaps and leaps are over short distances, usually one meter or less. All five species, regardless of body size or the availability of forest supports, prefer mediumsized supports. Incorporating our work from Uganda with previous investigations of positional behavior reveals few consistent trends with respect to body size or habitat use across primates. © 1995 Wiley-Liss, Inc.     

Distribution,population density,and status of sympatric cercopithecids in the Campo-Ma’an area,southwestern cameroon

A study on species composition, distribution, and population density of cercopithecids in the Campo-Ma’an area, Southwestern Cameroon, was undertaken from December 1997 until August 2000. A total of 665.5 km of line transects was used for the census. Thirteen diurnal primate species including five endangered species (Gorilla g. gorilla, Pan troglodytes, Mandrillus sphinx, Colobus satanas, Cercocebus torquatus) were recorded in the Campo Forest, the greatest part of which is a logging concession.Cercopithecus nictitans (1.43 groups/km²),C. cephus (1.13 groups/km²),C. pogonias (0.81 groups/km²), andC. torquatus (0.51 groups/km²) occurred at medium frequencies compared to figures from other Central African study sites. Mandrill densities estimated (0.27 groups/km²) show that the area is very important for the conservation of this rare species. Guenon densities found inside areas with a high level of human activities did not differ significantly from densities estimated in areas with a lower level of human activities.C. torquatus densities were significantly higher in the areas with a low level of human disturbance and encounter rates withLophocebus albigena also indicate a preference of less disturbed areas. Mangabeys are thus likely to be adversely affected by human activities in the area. In the Ma’an Forest, which has not been logged yet, ten species were confirmed. The population densities of two guenons (C. nictitans andC. cephus) were estimated to be twice as high in the unlogged forest area as compared to the logged forest of Campo. Other species are rarer in the Ma’an Forest than in the Campo Forest. Although mangabeys are adversely affected by human activities, the results still indicate that selective logging may be compatible with the conservation of cercopithecids, if a reduced damage logging concept and antipoaching measures are implemented. Increased hunting activities following logging operations will definitely have a negative longterm impact on primate populations in the Campo-Ma’an area if no further, more effective conservation measures will regulate wildlife use in future.     

High Prevalences and a Wide Genetic Diversity of Simian Retroviruses in Non-human Primate Bushmeat in Rural Areas of the Democratic Republic of Congo

Like the majority of emerging infectious diseases, HIV and HTLV are of zoonotic origin. Here we assess the risk of cross-species transmissions of their simian counterparts, SIV and STLV, from non-human primates (NHP) to humans in the Democratic Republic of Congo (DRC). A total of 331 samples, derived from NHP bushmeat, were collected as dried blood spots (DBS, n = 283) or as tissue samples (n = 36) at remote forest sites mainly in northern and eastern DRC. SIV antibody prevalences in DBS were estimated with a novel high throughput immunoassay with antigens representing the actual known diversity of HIV/SIV lineages. Antibody-positive samples were confirmed by PCR and sequence analysis. Screening for STLV infection was done with universal primers in tax, and new strains were further characterized in LTR. SIV and STLV infection in tissue samples was done by PCR only. Overall, 5 and 15.4% of NHP bushmeat was infected with SIV and STLV, respectively. A new SIV lineage was identified in Allen’s swamp monkeys (Allenopithecus nigroviridis). Three new STLV-1 subtypes were identified in Allen’s swamp monkeys (Allenopithecus nigroviridis), blue monkeys (Cercopithecus mitis), red-tailed guenons (Cercopithecus ascanius schmidti) and agile mangabeys (Cercocebus agilis). SIV and STLV prevalences varied according to species and geographic region. Our study illustrates clearly, even on a small sample size from a limited number of geographic areas, that our knowledge on the genetic diversity and geographic distribution of simian retroviruses is still limited and that humans continue to be exposed to relative high proportions on infected NHP bushmeat.     

Blood markers and genetic evolution in Cercopithecinae

Serum proteins and RBC enzymes were surveyed in 16 species (183 animals) of African guenons (tribe Cercopithecini) in order to determine their genetic polymorphism and to establish dendrograms on the basis of their allele frequencies. The molecular data obtained were compared with those of mangabeys (16 animals tested) and discussed in the light of our results inPapio andMacaca. The species surveyed wereCercopithecus neglectus, C. hamlyni, C. l'hoesti (C. l'h. l'hoesti, C. l'h. preussi, andC. l'h. solatus), C. nictitans, C. mitis (C. m. kolbi, C. m. albotorquatus, C. m. stuhlmanni, andC. m. albogularis), C. cephus, C. ascanius, C. erythrotis, C. petaurista, C. mona, C. pogonias, C. wolfi, andC. aethiops, Miopithecus talapoin, Allenopithecus nigroviridis andErythrocebus patas, Lophocebus albigena, andCercocebus torquatus. Eleven loci (ten systems) were studied in red blood cell enzymes and the Gc, Gm, Km, and Bm systems in DBP and immunoglobulin serum proteins. Most of the loci were polymorphic. Similar and different polymorphisms occur in closely related species or subspecies, particularly inCercopithecus. Guenons have phenotypes clearly distinct from mangabeys.     

The cost of living in larger primate groups includes higher fly densities

Flies are implicated in carrying and mechanically transmitting many primate pathogens. We investigated how fly associations vary across six monkey species (Cercopithecus ascanius, Cercopithecus mitis, Colobus guereza, Lophocebus albigena, Papio anubis, and Piliocolobus tephrosceles) and whether monkey group size impacts fly densities. Fly densities were generally higher inside groups than outside them, and considering data from these primate species together revealed that larger groups harbored more flies. Within species, this pattern was strongest for colobine monkeys, and we speculate this might be due to their smaller home ranges, suggesting that movement patterns may influence fly–primate associations. Fly associations increase with group sizes and may thus represent a cost to sociality.

     

The primate community of the Lopé reserve,Gabon: Diets,responses to fruit scarcity,and effects on biomass

The diets of all diurnal primates (Gorilla g. gorilla, Pan t. troglodytes, Mandrillus sphinx, Colobus satanas, Cercocebus albigena, Cercopithecus nictitans, C. pogonias, C. cephus) in the Lopé Reserve, central Gabon, are described from qualitative and quantitative data collected over 10 years. A total of 397 foods were recorded, of which 91% were from plants. The diets of seven of the eight species were numerically dominated by fruit, the exception being Colobus satanas with a diet dominated by seeds. When proportion of feeding time was examined, fruit remained the dominant food class for six species, while Cercocebus albigena, like the black colobus, spent most time feeding on seeds. The number of foods recorded per species ranged from 46–220, but dietary breadth of the four species that have not been subjects of detailed study was certainly underestimated. Almost half of the foods (46%) were eaten by only one species, and only four (1%) were recorded for all eight species. At Lopé, fruit is scarce for 2–3 months during the annual dry season, and fruit crop failures can prolong this period of scarcity to as many as 8 months in some years. When fruit is scarce, the diets of all species changed to include more nonfruit foods, but chimpanzees and the three species of guenons maintained a fruit dominated diet. The total biomass of the Lopé primate community is 374 kg/km², which is low compared to other sites in tropical Africa. Within the Lopé community, biomass correlates negatively with degree of frugivory, suggesting that fruit availability may be critical, but this does not explain the low total biomass compared to other sites. Neither floristic diversity nor the composition of the primate community at Lopé can account for the low biomass. While historical events such as climate-induced changes in forest cover, disease, or impact of human activities cannot be ruled out, we conclude that the most likely explanation of low primate biomass is the occurrence of an ecological “catastrophe” in the fairly recent past from which populations have not yet recovered. We believe that the most likely scenario was climate-mediated disturbance of flowering of important fruit food species. Prolonged fruit scarcity would have caused mortalities and affected the most frugivorous species more severely. Am. J. Primatol. 42:1–24, 1997. © 1997 Wiley-Liss, Inc.     

Mixed-species primate groups in the kibale forest: Ecological constraints on association

Five species of diurnal primates in the Kibale Forest of western Uganda— red colobus (Colobus badius),black- and- white colobus (Colobus guereza),redtail monkeys (Cercopithecus ascanius),blue monkeys (Cercopithecus mitis),mangabeys (Cercocebus albigena)-often associate in mixed- species groups that vary in size and composition from day to day. Across this range of species, we found no consistent effect of association on feeding rate. In addition, there is no systematic difference between the species- specific individual feeding rates when animals were in mixed- species groups feeding in a specific tree on one day and when individuals of one of the same species were feeding in the same individual tree on a subsequent day. If associating in a mixed- species group lowers the risk of predation, one might expect that the number of vigilant events would decrease in mixed- species groups. However, the only species to exhibit a consistent decrease in vigilant behavior when in association was the red colobus. Redtail monkeys were more vigilant when in association. We predicted that the density and distribution of food resources would both constrain the frequency of association and the size of mixed- species groups. Based on 22 months of data on food resources and bimonthly censuses, we found no relationship between the frequency of association (except mangabeys) or mean mixed- species group size and the density and distribution of food resources for all species. Finally, we examined the behavior of the monkeys in and out of association before and after the playback of a crowned hawk eagle call (Spizaetus coronatus),a known predator. When more species were in association, the amount of time they spent being vigilant following the playback was greater and the response more intense than when fewer species were in association or when the group was alone. The results of this study illustrate that the nature of the costs and benefits of polyspecific associations for these different monkey species are complex and vary from species to species.     

Monkey Abundance and Social Structure in Two High-Elevation Forest Reserves in the Udzungwa Mountains of Tanzania

The effects of human activity on population and social structure are a pantropical concern for primate conservation. We compare census data and social group counts from two forests in the Udzungwa Mountains, Tanzania. The main aim is to relate differences within and between the forests to current theory on the effect of human disturbance on primate abundance and group size. The survey reveals the presence of the restricted-range red colobus, Procolobus gordonorum, in New Dabaga/Ulangambi Forest Reserve (NDUFR). The primate community of NDUFR is impoverished compared to that in Ndundulu forest. Red colobus and black-and-white colobus (Colobus angolensis palliatus) abundance and group size are lowest in NDUFR. Fission-fusion of red colobus social groups may be occurring in previously logged areas of both forests. Our observations are consistent with current theory on the effect of habitat degradation and hunting on primates, but the relative effects of the 2 factors could not be differentiated. We pooled the results with previous data to show that abundance of red colobus in the Udzungwa Mountains is lowest at high elevations. Low red colobus group sizes appear to be related to human activity rather than elevation. Black-and-white colobus and Sykes monkeys (Cercopithecus mitis) show no relationship with elevation. Future studies will require more detailed information on vegetation, diet and ranging patterns to interpret fully intraspecific variation in population demography and social structure in the Udzungwa Mountains.     

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.

Interspecific interaction of the primate groups in Kibale Forest,Uganda

An ecological survey on the influence of interspecific interaction of the primates upon the distribution of their group ranges was carried out in 100 ha of the isolated forest northern outskirts of Kibale Forest in western Uganda, Africa. The study period of 105 days was from the 12th of November, 1970 to the 24th of February, 1971, including a preliminary survey of about two months. The subjects of this study are five species of primates, i.e., black and white colobus (Colobus polykomos), red colobus (Colobus badius), red tailed monkey (Cercopithecus ascanius), blue monkey (Cercopithecus mitis), and vervet monkey (Cercopithecus aethiops), which inhabited the study area. The red colobus group is thought to be the most influential of the five in the interspecific interaction.     

Fragmented living: Behavioural ecology of primates in a forest fragment in the Lopé Reserve, Gabon

A 17-month study was made of the primates using a 9-ha “island” of forest, surrounded by savanna, in the northern part of the Lopé Reserve, Gabon. One group ofCercopithecus cephus (plus a young maleCercopithecus nictitans who was in permanent association with them) were resident in the fragment and groups of five other species of primates made visits during 127 days of observation:Pan troglodytes, 15 visits;Cercocebus albigena, 10;Colobus satanas, 3;Cercopithecus nictitans, 2;C. pogonias, 1. Visits were also made by lone males of three species,C. nictitans, Cercocebus albigena, andMandrillus sphinx. The eighth species of diurnal primate present at Lopé,Gorilla g. gorilla, did not visit the fragment during the study. Compared to conspecific groups in neighbouring continuous forest, primates in the fragment ate less fruit, seeds and flowers and more insects and leaves. The local population density of primates resident in the fragment was equivalent to that of the neighbouring continuous forest where all eight species occur, despite the diversity and abundance of fruit being less in the fragment. The costs imposed on the resident group by the reduced diversity and availability of preferred fruit foods appeared to be offset by a number of benefits that increased individual feeding efficiency for monkeys residing within a single fragment. These included lower travel costs, reduced feeding competition between individuals through group fission, and excellent knowledge of the location and quality of food resources in the small home range. It is also possible that the overall negative impact of inter-specific feeding competition was lower in fragments than in continuous forest and that micro-habitat differences resulted in an increased availability of palatable insect and leaf fallback foods in the fragment.     

Upperlimb skeletal elements of miocene cercopithecoids from east Africa: Implications for function and taxonomy

Old collections and unpublished newly-discovered specimens of Miocene cercopithecoids studied here include humeri and proximal ulnae from Maboko (KNM MB 2, KNM MB 3, KNM MB 19, KNM MB 32, KNM MB 12038, KNM MB 12044), Nyakach (KNM NC 9824) in Kenya and from Napak (NAP V-8.85) in Uganda. This work leads to the conclusion that two different groups of monkeys may have co-existed in East Africa in the Middle Miocene. After comparison with extant cercopithecoids (Colobus polykomos, Colobus badius, Colubus angolensis, Colobus guereza, Cercopithecus aethiops, Cercopithecus ascanius, Nasalis larvatus, Presbytis entellus and severalPapio andMacaca), the fossils can be divided into two morphological groups. In the distal humerus, the shape of thetrochlea humeri and the orientation of theepicondylus medialis are distinctive; in the ulnae, the distinction is mainly based on the morphology of theincisura trochlearis. Thus, we would have a more terrestrial group and a more arboreal one. The differences (not linked with sex) are large enough to indicate a taxonomic difference (as proposed on the teeth collected to the same sites, by several authors). At this stage, we cannot assign with certainty the specimens to one taxon or the other (Victoriapithecus macinnesi orVictoriapithecus leakeyi).     

Impact of Commercial Hunting on Monkey Populations in the Taï region,Côte d'Ivoire1

We studied the impact of hunting on monkey species in the Taï National Park and adjacent forests in Côte d'Ivoire. The average wild meat consumption per capita per year was assessed from market surveys and interviews. We determined that the amount of primate wild meat being extracted in the Taï National Park and surrounding forests was 249 t in 1999. Hunting pressure was the highest on the larger primate species such as red colobus, Procolobus badius, black and white colobus, Colobus polykomos, and the sooty mangabey, Cercocebus torquatus atys. Estimates of population densities were based on line transect surveys. The maximum annual production of each species was calculated using the Robinson and Redford model (1991) and assuming unhunted conditions. Comparing current harvest levels with the maximum sustainable yield suggests that harvest of red colobus monkeys (Procolobus badius) is sustainable, whereas current off‐take of the black and white colobus (Colobus polykomos), the sooty mangabey (Cercocebus atys), diana monkeys (Cercopithecus diana), and Campbell's monkeys (Cercopithecus campbelli) exceeds sustainability by up to three times.     

Effects of Forest Fragmentation on the Abundance of <Emphasis Type="Italic">Colobus angolensis palliatus</Emphasis> in Kenya’s Coastal Forests

We documented the occurrence and abundance patterns of Angola black-and-white colobus (Colobus angolensis palliatus) in 46 coastal forest fragments ranging from 1 ha to >1400 ha in the Kwale District, Kenya. In field surveys conducted in 2001, we also recorded forest spatial, structural, resource, and disturbance characteristics to determine the effects of habitat quality and fragmentation and the factors most critical to the continued survival of the little-known species. We tested 13 hypotheses to explain variation in patch occupancy and abundance patterns of Colobus angolensis palliatus in relation to habitat attributes. Minimal adequate models indicated that the occurrence of colobus in forest fragments is positively associated with fragment area and canopy cover, whereas the density of colobus in occupied fragments is attributable to forest area, the proportion of forest change over the previous 12 yr, and the basal area of 14 major food trees. Large-scale illegal extraction of major colobus food trees in the District for human resource use, in both protected and unprotected forests, together with ongoing forest clearance and modification, are the major threats to Colobus angolensis palliatus in Kenya.     

Behavior of bonobos (Pan paniscus) following their capture of monkeys in Zaire

For the first time, three cases of capture and forced interaction were observed between bonobos (Pan paniscus)and two other species of primates (Colobus angolensisand Cercopithecus ascanius)in the Lilungu (Ikela) region, Republic of Zaire. The bonobos interacted with the captured primates as if they were dealing with individuals of their own species. They sought cooperation in their interactions with the captured young primates without scccess. There is no evidence that they ate the captives.     

Densities,Distributions, and Seasonal Movements of Gorillas and Chimpanzees in Swamp Forest in Northern Congo

The conservation of gorillas (Gorilla spp.) and chimpanzees (Pan troglodytes) depends upon knowledge of their densities and distribution throughout their ranges. However, information about ape populations in swamp forests is scarce. Here we build on current knowledge of ape populations by conducting line transect surveys of nests throughout a reserve dominated by swamp forest: the Lac Télé Community Reserve in northern Congo. We estimated gorilla and chimpanzee densities, distributions across habitats, and seasonal changes in abundance. Gorilla density was 2.9 gorillas km^–2, but densities varied by habitat (0.3–5.4 gorillas km^–2) with highest densities in swamp forest and terra firma mixed forest. Average chimpanzee density is 0.7 chimpanzees km^–2 (0.1–1.3 chimpanzees km^–2), with highest densities in swamp forest. Habitat was the best predictor of ape nest abundance, as neither the number of human indices nor the distance from the nearest village predicted nest abundance. We recorded significantly greater numbers of apes in terra firma forest during the high-water season than the low-water season, indicating that many gorillas and chimpanzees are at times concentrated in terra firma forest amid a matrix of swamp forest. Seasonally high numbers of apes on terra firma forest islands easily accessible to local people may expose them to substantial hunting pressure. Conversely, the nearly impenetrable nature of swamp forests and their low value for logging makes them promising sites for the conservation of apes.     

In Vitro Fermentation of Dietary Carbohydrates Consumed by African Apes and Monkeys: Preliminary Results for Interpreting Microbial and Digestive Strategy

Primates derive significant nutritional benefits from hosting symbiotic, fermenting microbes in their gut, including the provision of energy from short-chain fatty acids (SCFAs). We measured fermentation parameters in fecal samples of 4 hindgut fermenting species (Gorilla gorilla, Pan troglodytes, Papio hamadryas, Cercopithecus neglectus) and 1 foregut fermenting species (Colobus guereza) to determine whether differences in SCFA profiles exist between the 2 digestive systems. We analyzed SCFA profiles, culture pH, and methane from fecal samples collected at the North Carolina Zoological Park. Results indicate that the captive individuals exhibit high total SCFA concentrations, with a particularly high acetate-to-propionate ratio. Methane levels were highest in the 2 ape species, and lowest in Colobus guereza and Cercopithecus neglectus. Total SCFA concentrations were similar between wild and captive-born Gorilla gorilla, although concentrations of acetate were significantly greater —and butyrate concentration and methane production significantly lower— in wild-caught gorillas relative to captive-born. These results are consistent with data on diet and digestive retention times among Catarrhini and have implications for our understanding of the interactions among diet, body mass, digestion, and how monogastric cercopithecines can consume either similar or greater levels of fiber than larger-bodied apes.     

Association of Terrestrial Mangabeys (Cercocebus atys) with Arboreal Monkeys: Experimental Evidence for the Effects of Reduced Ground Predator Pressure on Habitat Use

We examined the behavior of two arboreal monkeys—Piliocolobus badius (western red colobus) and Cercopithecus diana (Diana monkey)—in the presence and absence of a third, predominately terrestrial monkey, Cercocebus atys (sooty mangabey) in the Ivory Coast's Taï Forest. Via experimental data, we show that sooty mangabeys are effective sentinels for ground predators. Then we compared strata use of red colobus and Diana monkeys in the presence and absence of mangabeys. Our data indicate that red colobus and Diana monkeys descend to low forest levels and to the forest floor significantly more often when mangabeys are spatially intermingled with them, i.e. in polyspecific associations. The niche extension may provide some foraging advantage, especially for red colobus. We identified the specific causal agent—relaxed ground predator pressure—of a temporary shift in habitat use. In this instance, the presence of one species (Cercocebus atys) leads to the temporary expansion of a niche normally avoided by others Piliocolobus badius and Cercopithecus diana.