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Diet and habitat preference of Mandrillus sphinx in gabon Implications of foraging strategy.

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American Journal of Primatology 11:9-26 (1986)
Diet and Habitat Preference of Mandrillus sphinx in Gabon:
Implications of Foraging Strategy
SALLY A. LAHM
Zoological Society of S a n Diego
An ecological study of the mandrill was conducted in northeastern and
central Gabon from November 1982 to October 1983. The purpose of the
study was to gather basic ecological data on the mandrill as a foundation
for a future long-term study of this species. Data were collected by direct
observation, by collecting evidence left along fresh trails, and by fecal and
stomach content analyses. Fruits constituted the mandrill’s major dietary
item, supplemented by various plant parts and numerous insect species.
Small vertebrates were also occasionally consumed. Mandrills fed primarily
on the forest floor but also climbed trees to obtain food, probably on a more
frequent basis than do the Papio species. The majority of mandrill sightings
and identified foods were attributed to primary forest, but foraging also
occurred in secondary, riparian, and inundated forests. The patchy distribution and seasonal fluctuation of fruiting trees in the rainforests of Gabon
may influence mandrill home range usage. The eclectic feeding behavior
and large home ranges estimated for mandrill groups suggest that this
species may play a n important role in seed dispersal. Interspecific competition for food sources may be mitigated by species’ preferences for different
fruit parts. The mandrill is able to utilize foods in both arboreal and terrestrial ecological niches.
Key words: mandrill, ecology, seed dispersal, competition
INTRODUCTION
The behavior and ecology of the mandrill (Mandrillus sphinx) are scarcely
known. Short-term studies of the mandrill by Jouventin [1975] and Sabater Pi [1972]
provided the only information about this elusive species until the recent publication
by Hoshino et a1 [1984] of a n extended study of mandrill ecology in Cameroon.
Despite these commendable efforts, the socioecology of mandrills is still not known
in detail owing to their timidity, wide-ranging habits, and densely vegetated habitats.
The mandrill is the largest member of the Cercopithecinae. Adult males attain
weights of 30-40 kg, while females are nearly half the size of the males [Dorst &
Received October 29, 1985; revision accepted March 11, 1986.
Address reprint requests to Sally A. Lahm, Department of Anthropology, New York University, 25
Waverly Place, New York, NY 10003.
0 1986 Alan R. Liss, Inc.
10 / Lahm
Dandelot, 19701. To justify the placement of the mandrill in a genus separate from
that of Papio, Napier and Napier [1967] and Jolly [1970] have cited a number of
morphological characters related to the facilitation of increased branch-walking and
fruit-processing as evidence of the mandrill's considerable divergence from the Papio
species.
The geographical distribution of the mandrill has not been definitely determined. Grubb [1973] proposed that the mandrill occurs in Cameroon south of the
Sanaga River, Rio Muni, Gabon, and Republic of the Congo. The southern and
eastern limitations of its range are not known, although the Ivindo River is purported to be a barrier to the mandrill's eastward extension in Gabon [Jouventin,
19751. The mandrill is officially listed as a n endangered species owing to hunting
pressure and habitat alteration throughout its limited range [Wolfheim, 19841.
Study Areas
Gabon is situated on the equator (3'N-3'S) on the west central African coast
between longitudes 8" and 15" E. It covers a n area of 267,667 km2 and is composed
of 15% savannah and 85%tropical rain forest. The climate is characterized by two
dry and two rainy seasons annually. Amounts of rainfall vary among different
regions, ranging from 1,200 mm annually in the southeast to 3,200 mm along the
coast [Hladik, 19781.
Field work was conducted in two distinct geographical areas (Fig. 1). The
northeastern region near Makokou is characterized by high diversity of vegetation
and continuous rainforest. More than 900 species of plants have been identified, the
dominant tree species consisting of the subfamilies Mimosoideae and Papilinoideae
[Caballe, 1978; Florence & Hladik, 19801. The temperature averages 24"C, with
humidity remaining constant near 85%. Rainfall averages 1,700 mm annually
[Hladik, 19781.
CAMEROUN
1
- )
CONGO
-0
.
,............,..............
200 Km
STUWSITES
Fig. 1. Locations of study areas in Gabon (reprinted from Primate Conservation by permission, S. Nash).
Diet and Habitat Preference of Mandrill / 11
The Reserve de Lope-Okanda in central Gabon comprises 5,000 km2 of savannah, gallery, and hill forests at 200-500 m elevation. Rainfall averages 1,600 mm
annually. Although there is a considerable overlap of plant species between the two
ecological zones, the floristic composition of the central region is dominated by the
families Cesalpiniaceae and Myristicaceae [Caballe, 1978; de Saint Aubin, 19631.
METHODS
An ecological study of the mandrill was conducted in northeastern and central
Gabon from November 1982 to October 1983 based a t the Institut de Recherche en
Ecologie Tropicale near Makokou. Data were gathered by direct observation, by
collecting evidence left along fresh trails, and by fecal and stomach content analyses.
Initial surveys were conducted in several localities in northeastern and central
Gabon, while actual field work was done in the vicinity of the Institute and at the
Reserve de Lope-Okanda in central Gabon. The study yielded data on mandrill diet
and habitat preference and additional information regarding group size, composition, defense, and predation.
Mandrills were observed during 14 encounters, ranging from 17 to 210 minutes
and averaging 72.5 minutes duration, for a total of 16.91 hours of stationary visual
contact. Much additional time was logged while following groups, since the rough
terrain, dense vegetation, and animals’ timidity prevented prolonged contact and
observation. Groups rarely remained in one location for longer than 10-20 minutes.
All collected fecal samples were preserved in 10% formalin solution and labeled
according to date and location for future microscopic analysis. It was not possible to
attribute fecal samples to individual mandrills.
Since frequent and prolonged observation was not possible, additional dietary
information was collected by performing stomach content analysis. Although the
mandrill is hunted and consumed by the rural population, i t is not frequently
encountered on hunting forays. Arboreal monkeys and Cephalophus (duiker) species
are the major game sources of protein for native inhabitants. Of the 12 mandrill
stomachs and skulls acquired from local hunters, six were attributed to adult males,
one to a juvenile male, three to juvenile females, and two to adult females. Assessment of age and gender were provided from cranial and dental measurements of the
specimens and through information from native hunters.
Stomach contents were dried, weighed, and filtered through several sieves of
varying mesh sizes. The remnants of each sieving were sorted into various food
categories with a binocular microscope. These included fruits and seeds; invertebrates; bark, leaves, stems, and fiber; earth; and fungi. Fruits and seeds were placed
in the same category, since it was not always possible to separate seeds from fruit
pulp. Bark, leaves, stems, and fiber were combined, as they appeared frequently but
in minute portions. Each food category was weighed separately. Fecal samples were
prepared similarly [Gautier-Hion, 19801. Forty-one percent of all dietary items were
collected during direct observation, with fecal and stomach content analyses contributing 30% and 29%, respectively.
The value of these two methods in primate diet analysis has been discussed
[Moreno-Black, 19781. While it is true that fecal and stomach content analyses do
not accurately reflect a species’ entire dietary regime but only that which has
recently been eaten, this bias is compensated for by variations in the localities and
seasons of collections. Since it was not possible to positively identify mandrill groups
and since fecal samples and stomach contents were collected in substantially separated areas within both ecological zones, it is thought that the results of the analyses
are representative of a number of different groups. The small sample size (63 scats,
12 stomachs) offers limited interpretation but may reflect seasonal availability and
12 I Lahm
preference of food items. Some invertebrates, in particular, were accorded only
familial taxonomic status owing to the scant remains available. Most insect and
animal specimens consisted of fragmented body parts. Not all botanical specimens
were identifiable. In some cases, a few seeds were the only evidence of a fruit species’
consumption.
RESULTS
Plant Foods
Sixty-three species of plants and fruits in 27 families were identified as mandrill
foods. Of these, the families Annonaceae, Sapotaceae, and Olacaceae were the best
represented. Large fruit-bearing plants predominated as food sources: 72% were
trees, 9%were lianas, and 11% were undetermined. Other plant parts eaten included
leaves, bark, stems, and fiber. Herbaceous plants, which constituted 8%of the plant
foods consumed, produced small amounts of fruit (four of five determined species),
but may have been more important for the nutrition provided by their young shoots
and stems. Fifty-four percent of all identified foods were collected in the central
region, while 46%originated in the northeast.
Table I lists all plant species, parts consumed, location of collection, habitat, and
vegetation types. Fruiting trees are grouped by size; 40% are taller than 20 m, 53%
are between 8 and 20 m, and 7% are less than 8 m tall.
Since seeds and plant parts were the dietary items most frequently found in the
fecal samples, it was not always possible to tell what parts of fruit other than seeds
were ingested. The difficult field conditions precluded close observation of actual
feeding behavior. Most plant species collected during direct observation were remnants of partially ingested items.
The kernel of the nut-like fruit, C o d a edulis (Olacaceae), was consumed, and
the hard covering was discarded. In the Myristacaceae, whose aromatic 3-4-cm
fruits contain a brightly colored aril enclosing a single seed, the evidence implies
that only the seed andor aril was eaten.
Small and medium-sized fruits with abundant small seeds dispersed throughout
the fruit were usually consumed whole. It appears that ripe fruits are mostly
preferred, although unripe fruit appearing a t the beginning of the fruiting season
may also be eaten. The unripe pulp of Irvingia gabonensis (wild mango) was partially
consumed, and the pit was opened to obtain the single seed. The pulp and seeds of
Annonidium mannii, a large, soft fruit 20-30 cm long and often in excess of 10 kg,
may provide food for several individuals.
Most of the bark, leaves, and stems in the fecal and stomach contents were in
minute quantities and sizes or partially digested, and were, therefore, too difficult
to distinguish. Blades of the grass Atractocarpa olyraeformis, found in two fecal
samples, were large (3-5 cm) and intact, indicating that they were probably not
easily digestible.
Domesticated Plant Species
Native inhabitants reported incidents of mandrills consuming plantation crops,
such as Elaeis guineensis (palm nut) and Manihot utilissima (manioc), both of which
have been cited as mandrill foods [Sabater Pi, 1972; Jouventin, 19751. Other cultivated plants mentioned were bananas, mangos, pineapples, papayas, and avocados.
The major dry season (July through August), when plant foods in the forest are least
available, was cited as the time of most frequent mandrill incursions into cultivated
areas.
Burseraceae
Apocynaceae
Annonaceae
Anacardiaceae
Family
Pseudospondias longifolia
(Engl.)
Trichoscypha acuminata
Annonidium mannii
Engl. & Diels
Hexalobus crispiflorus
A. Rich.
Pachypodanthium barteri
(Benth) Hutch
Polyalthia suaveolens
Engl. & Diels
Xylopia staudtii
Engl. & Diels
Indeterminate species (1)
Dictyophleba stipulosa
(S. Moore ex Wernham) Pichon
Pterotaberna inconspicua
(Stapf) Stapf
Dacryodes buttneri Engl.
Dacryodes edulis
(G.Don) Lam
Dacryodes klaineana
(Pierre) Lam
Species
3
-
I
I
I
I11
I
I11
-
I
I
1,II
I
I
C
N
C
C
N
C
N
N
C
N
N
N
Fruit pulp
Fruit, seeds
Entire fruit
Ripe, unripe
Fruit pulp
Fruit, seed
Seeds
Fruit, seed
Fruit, seed
Fruit pulp
Fruit pulp
Fruit pulp
Fruit pulp
(continued)
3
3
3
1
L
2
2
3
2
2
2
I
N
Fruit pulp
Vegetation
type
Habitat
Location
Parts eaten
TABLE 1. Identification of Plant Species Consumed by Mandrills: Parts Consumed, Geographical Location, Habitat, and
Vegetation Type*
Hippocrateaceae
Guttiferae
Graminae
Euphorbiaceae
Dilleniaceae
Ebenaceae
Dichapetalaceae
Caesalpiniaceae
Family
Detarium macrocarpum
Harms
Dialium pachyphyllum
Harms
Dialium sp.
Guibourtia tessmanii
(Harms) J. Leonard
Dichapetalum sp.
Dichapetalum sp.
Tetracera sp.
Diospyros cra-ssiflora
Hiern
Diospyros zenkeri
(Gurke) F. White
Alchornea firibunda
Mull. Arg.
Discoglypremna caloneura
Prain
Uapaca heudelotii Baill.
Uapaca sp.
Atractocarpa olyraeformis
Franch.
Pentadesma butyracea
Sabine
Salacia sp.
Species
2
2
3
L
L
L
2
2
1
3
I
-
-
I
I
I
N
C
C
N
N
C
N
N
Fruit, seeds
Fruit, seeds
Fruit pulp
Fruit, seed
Fruit, seed
Seed
Fruit pulp
Fruit pulp
HP
2
L
I
I
-
Fruit, seeds
Pulp, seeds
2
2
N
C
-
I11
N
Fruit, seeds
Seeds
Grass blade
N
N
1,II
C
N
Entire fruit
Pith of trunk
I
3
I
C
Fruit pulp
Vegetation
type
Location
Parts eaten
Habitat
TABLE I. Identification of Plant Species Consumed by Mandrills: Parts Consumed, Geographical Location, Habitat, and
Vegetation Type* (Continued)
Myristicaceae
Moraceae
Mimosaceae
Marantaceae
Icacinaceae
Irvingiaceae
Indeterminate species (1)
Irvingia gabonensis
(Aubry-Lecomte ex ORorke)
Baill.
Klainedoxa gabonensis Pierre
Ataenidia conferta
(Benth.) Milne-Redh.
Sarcophrynium brachystachy
(Benth.) K. Schum
Pentaclethra macrophylla
Benth.
Ficus sp.
Ficus sp.
Musanga cecropiodides R. Br.
Myrianthus arboreus
(P. Beauv.)
Pycnanthus angolensis
(Welw.) Warb.
Staudtia gabonensis Warb.
N
N
C
C
C
C
Fruit, seeds
Fruit, seeds
Fruit pods
Pulp, seeds
Aril, seed
Aril, seed?
C
I
1,II
1,II
-
(continued)
3
3
2
2
2
HP
I11
N
1,II
3
HP
I
I
rq
C
3
I
Fruit, seeds
Fruit, base of
young shoots
Fruit, base of
young shoots
Seeds
-
-
C
C
Seeds
Fruit, seeds
Aframomum sp.
Lophira alata
Coula edulis Baill.
Diogoa zenkeri
(Engl.) Exell & Mend.
Heisteria sp.
Olax sp.
Ongokea gore Pierre
Ancistrophyllum sp.
Calamus deeratus
Mann & Wendl.
Deidamia sp.
Nauclea didderrichii
(DeWild & Th. Dur.) Merrill
Blighia welwitschii
(Hiern) Radlk.
Baillonella toxisperma
Pierre
Gambeya boukokoensis
Gambeya lacourtiana
Gambeya sp.
Indeterminate species (4)
Cissus sp.
Aframomum giganteum
Species
C
L
HP
HP
-
I1
-
-
-
3
-
C
C
C
N,C
C
N
Seeds
Pulp, seeds
Seeds
Seeds
Seeds
Fruit, seeds,
hearts of stems
Fruit, seeds
I
3
I
C
Entire fruit
I
3
I
N
Pulp, seeds
L
2
I
2
2
I
C
C
Pulp, seeds
Fruit pulp
-
3
3
3
Vegetation
type
3
2
2
C
N
N
N
N
Entire fruit
Pulp, seed
Pulp
Entire fruit
Entire fruit
I
I
1,111
Habitat
I11
I11
C
C
C
Location
Fruit, seed
Pulp
Pulp, seed
Parts eaten
*Location: N, North Gabon; C, Central Gabon. Habitat: I, Primary forest; 11, Secondary and Forest Edge; 111, Riparian and Inundated Forest.
Tree sizes: 1,less than 8 m; 2, 8-20 m; 3, more than 20 m. L, liana; HP, herbaceous plant; -, undetermined.
Vitaceae
Zingiberaceae
Sapotaceae
Sapindaceae
Passifloraceae
Rubiaceae
Palmaceae
Ochnaceae
Olacaceae
Family
TABLE I. Identification of Plant Species Consumed by Mandrills: Parts Consumed, Geographical Location, Habitat, and
Vegetation Type* (Continued)
Diet and Habitat Preference of Mandrill / 17
Vertebrate Foods
Vertebrate foods appear to be taken infrequently on an opportunistic basis and
probably account for only a small fraction of the total food intake of mandrills. Table
I1 lists the number of determined vertebrate foods. All were discovered in the fecal
samples. In addition, the remains of a species of terrestrial crab of the family
Potamonidae was found in association with mandrill tracks in a streambed, indicating manipulation and perhaps consumption of the crab by one or more mandrills.
Nest raiding accompanied by the consumption of birds’ eggs and nestlings has also
been reported for mandrills [A. Brosset, personal communication], The low frequencies of animal foods (Fig. 4) suggest that their consumption may have been fortuitous
(i.e., occurring in the act of exploratory foraging).
Invertebrate Prey
The diverse array of invertebrate species consumed further illustrates the mandrill’s eclectic feeding behavior (Table 111). Beetles (Scarabeidae), ants (Formicidae),
and spiders (Araneida) were the most frequently consumed items. The eight species
of beetles, all dung feeders, construct their galleries directly below the dung pad,
which is used as a food source for the developing larvae. Since these were the only
species represented in the material examined, it can be safely assumed that the
adult beetles were collected on or under the dung rather than a t flowers, and
collection thus required inspection and manipulation of dung pads [D. Faulkner,
personal communication].
Among the 14 species of ants consumed, the five Odontomachus species and two
Polyrachis species were the most numerous. These species live in small colonies and
generally nest in dead trees or in soil underneath logs. The Odontomachus species,
in particular, are predaceous and aggressive. Other smaller scavenging species such
as Solenopsis may have been ingested along with fruit or plants [B. Darchen,
personal communication].
All specimens of Araneida prey are large, ground-dwelling, hunting spiders that
hide under rocks or leaf litter during the day and can also be found on tree trunks.
The remaining invertebrate prey were present in small numbers suggestive of
opportunistic feeding. The presence of larva and pupa of three invertebrate species
suggests that these nutritionally rich food sources were actively sought, since they
are typically found in rotting logs or under soil. Most of these soft-bodied immature
stages may have been destroyed during mastication.
Diversity of Food Species and Dietary Flexibility
Figure 2 illustrates the percentage of occurrence of fruit species and plant foods
in mandrill fecal samples and stomach contents. Plant foods included leaves and
fibrous plant matter from a variety of sources (stems, bark, petioles, etc.). Six percent
of the fecal specimens contained no seeds or evidence of fruiting species, but remnants of plant foods were noted. The greatest percentages of occurrence were in the
three to four fruit species category. Plant foods were present in 92% of the stomach
contents and in 51% of the fecal material.
The percentages of all foods procured from stomach contents may reflect seasonal availability, since 58% of the stomachs were collected from mid-June to midAugust, the major dry season and the critical period for abundance of all foods.
Consequently, stomach contents collected during more productive seasons may yield
a n increased number of fruit species. Most fecal samples were collected from September to May, when fruit was generally available.
The majority of identified fruit species (88%)were small to medium-sized (1-8
cm), with only two species exceeding 10 cm in diameter (Fig. 3). Extremely small
18 / Lahm
TABLE 11. Vertebrate Foods in Mandrill Fecal Samples (N
= 63)and Stomach Contents (N = 12)
Phylum: Chordata
Class: Reptilia
Order: Chelonia
Family: Testudinidae
Undetermined species (1)(tortoise)
Class: Amphibia
Order: Salientia
Undetermined species (1)(frog, aquatic?)
Class: Mammalia
Order: Rodentia
Family: Hystricidae
Genus: Atherurus africanus (Gray, 1842)
(African brush-tailed porcupine)
Family: Muridae
Genus: Malacomys longipes Milne-Edwards, 1877
(Swamp rat)
Order: Insectivora
Family: Soricidae
Genus: Paracrocidura schoutedeni de Balsac, 1956
(Shrew)
L
2
40
30
20
10
0
0
1
2
3-4
5- 7
Plant
Foods
Number o f Fruit Species
Fig. 2. Percentages of occurrence of fruit species and plant foods in mandrill fecal samples (N = 63) and
stomach contents (N = 12).
Diet and Habitat Preference of Mandrill / 19
50 -
45.
40 -
35 -
Fruit Sizes (cm)
Fig. 3. Percentages of fruit sizes consumed by mandrills, expressed as diametric measurements in
centimeters.
loot
9
8
7
-
5
6
:.
5
ul
C
3
P'
Y
3
2
1
Plants
Fruits
Insects
LL,
Fungi
Earth
Animal
Matter
Food Categories
Fig. 4. Frequencies of occurrence of food categories in mandrill stomach contents and fecal samples.
Animal matter includes all noninsect animal foods.
20 I Lahm
TABLE 111. Invertebrate Species Consumed by Mandrills
Phylum: Mollusca
Undetermined species (mollusc) (1)
Order: Coleoptera
Family: Scarabeidae
Tribe: Onthophagini
Genus: Onthophagus sp.
Diastellopalpus sp.
Proagoderus gibbiramus
Tribe: Onitini
Genus: Onitis sphinx?
Onitis subcrenatus?
Tribe: Oniticellini
Genus: Liatongus interruptus
Tribe: Coprini
Genus: Copris sp.
Catharsius sp.
Family: Brentidae
Undetermined species (1)
Undetermined Coleoptera species (adult) (1)
Undetermined Coleoptera species (larva) (1)
Order: Hymenoptera
Superfamily: Chalcoidea
Undetermined species (parasitic wasp) (1)
Family: Braconidae
Undetermined species (wasp) (1)
Family: Formicidae
Subfamily: Myrmicinae
Genus: Crematogaster clariuentris
Crematogaster striatula
Crematogaster sp.
Solenopsis sp.
Myrmicaria sp.
Subfamily: Dorylinae
Genus: Anoma nigricans
Subfamily; Ponerinae
Genus: Oclontomachus spp. (5)
Subfamily: Formicinae
Genus: Polyrachis spp. ( 2 )
Order: Hymenoptera
Family: Formicidae
Undetermined species (1) (pupa)
(continued)
fruits such as Discoglypremna caloneura (1cm) were often swallowed whole. Small
seeds are probably less susceptible to damage from mastication. Few fragmented
seeds were present in the analyzed materials.
Invertebrates may be highly valued food items (Fig. 4) as reflected by the
presence of insect remains in 100% of the stomach contents and 91% of the fecal
samples. It was not possible to determine whether the ingestion of earth (25%
frequency) was intentional (geophagy) or incidental. Captive mandrills have been
observed eating small particles of soil (author’s personal observation).
Relative Intake of Foods
Table IV shows the relative importance of the five categories of food found in
the stomach contents. The plant category includes leaves, stems, fibrous matter,
Diet and Habitat Preference of Mandrill / 21
TABLE 111. Invertebrate Species Consumed by Mandrills
(Continued)
Subfamily: Dolichoderinae
Undetermined species (1)
Class: Diplopoda
Undetermined species (1)(millipede)
Chilopoda
Undetermined species (1)(centipede)
Arachnida
Order: Araneida
Family: Sparassidae
Undetermined species (1)
Theraphosidae
Undetermined species (1)
Selenopidae
Undetermined species (1)
Clubionidae
Undetermined species (1)
Ctenidae
Undetermined species (1)
Order: Ricinuleida
Undetermined species (1)
Order: Acari
Family: Ixodidae
Undetermined species (1)(tick)
Order: Lepidoptera
Undetermined species (2) (adult, larva)
Order: Collembola
Undetermined species (1)(springtail)
Order: Hemiptera
Family: Nabidae
Undetermined species (1)(damsel bug?)
Reduviidae
Undetermined species (1)(assassin bug)
Undetermined Hemiptera species (3)
Order: Orthoptera
Undetermined species (2)(grasshopper)
Superfamily: Blattoidea
Undetermined species (2) (cockroach)
bark, and herbaceous plants. Fruits consist of fruit and seeds. Fruits, plants, and
insects formed the most important parts of the diet. Fruit was predominant, accounting for a n average of 88%of dry weight of stomach contents. Plants and insects each
averaged 5% of dry weight in the same stomachs. The quantity of fungi was
relatively low, but individual values varied, ranging from 1% to 4%. Earth-eating
was apparently relatively rare, since earth was found in only three of 12 stomachs,
where it averaged 2% of dry weight.
Seasonal variability could not be ascertained because most (58%)stomachs were
obtained during the 3 months of the major dry season. However, there was a general
tendency toward increased consumption of plants and decreased ingestion of fruits
and insects from June to August, when the latter are less abundant. Insects made
up slightly higher proportions than did plants in most individuals.
22 I Lahm
TABLE IV. Relative Intake of Different Food Categories for Mandrillus sphinx Expressed
as Percentages of Dry Weight in Stomach Contents (N = 12)"
Sex
1.F
2. F
3. M
4. F
5. M
6. M
7. M
8. M
9. F
10. M
11. F
12. M
Date
Dry wt. (g)
Plants
Fruits
Insects
Fungi
Earth
Dec 10
Dec 10
7.1
7.4
59.2
15.7
100.2
116.5
259.3
446.0
81.1
178.4
62.0
140.0
.04
.03
.04
.06
.09
.07
.10
.I1
.03
.02
.01
.03
.05
.89
.90
.91
.84
.86
.81
.05
.04
.05
.09
.05
-
.02
.03
-
-
May 18
Jun 21
Jul15
Jul23
Aug 04
Aug 11
Aug 16
Aug 16
Aug 23
Sep 09
Averages
.82
.84
.91
.90
.97
.92
.88
.08
.08
.05
.04
.04
.02
.05
.05
-
.01
-
.04
-
.01
.03
.01
-
-
.02
.02
-
*M, male; F, female.
Diet and Habitat
It was possible to determine the habitat of 77%of the 63 identified plant species.
The remaining 23% were difficult to identify beyond the familial or generic taxonomic levels. Of the 49 species determined a t the specific level, 71%occur in primary
forest, 14%in secondary and forest edge, and 14%in riparian and inundated forests.
Considering only fruiting tree species, i.e., excluding the 11 species of lianas and
herbaceous plants that also provide fruits, 74% occur in primary forest, 14% in
secondary and forest edge, and 12% in riparian and inundated forest habitat.
These percentages strongly suggest that mandrills in this region forage primarily in areas associated with mature forest tree species but also take food in other
habitats. No plants were typical of savannahs, which exist in the central study
region. This evidence is corroborated by the predominance of mandrill sightings in
this region on hillsides and plateaus in primary and secondary forests relatively free
of dense undergrowth and close to streams. Much of the secondary forest a t lower
elevations had a dense undergrowth of herbaceous plants from ground level to 3 m.
Mandrills were never observed in this habitat, nor on the savannah, although signs
(tracks, dung) of their crossing narrow expanses of savannah were noted. The
condition of the evidence suggested that the crossings occurred in the early morning
and late afternoon, when sunlight intensity was minimal.
In the northeastern study area, mandrills were seen only on plateaus and slopes
above streams or rivers where the undergrowth was less dense. Mandrill tracks
were also found along and in stream beds, indicating that groups forage in riparian
habitat in addition to obtaining water there. Sixty percent of identified animal foods
came from this habitat (Table 11).
DISCUSSION
Dietary Diversity and Forest Regeneration
The importance of primates as seed dispersers has been widely documented
[Hladik & Hladik, 1967; Liebermann et al, 19791. The mandrill's selection of a
diverse array of mature, fleshy fruits of which both seeds and pulp are consumed
suggests that it is a n important seed disperser for many plant species. CharlesDominique [1975] has demonstrated a complex dispersion of tree species in the
Diet and Habitat Preference of Mandrill I 23
tropical rainforest of Gabon. Fruiting trees are extremely scattered but yield an
abundant though localized crop. Those with a meager production of fruit are abundant, while those producing extensive amounts of fruit are rare and widely scattered.
If mandrill groups adapt their social organization and foraging strategies to the
seasonal availability of foods, their selection of a wide range of foods within a large
supplying area would disperse a variety of plant seeds over considerable distances.
Since fruits constitute the major portion of the mandrill’s diet, the large group
size and home range of this species suggest that mandrills may be important seed
dispersal agents. Hoshino et a1 [1984] estimated home-range sizes of mandrills in
Cameroon as 5 km2 for a group of 15 and 28.5 km2 for a group of 95. In contrast, the
home-range sizes of six sympatric arboreal primate species in Gabon vary from .1 to
2.0 km2 [Gautier-Hion, 19781.
Significance of Food Selection
The dietary choices and distribution of primate species may be affected by high
concentrations of toxins in plants [McKey, 19781. As Hladik [1977,1981]has shown,
plant species eaten by primates in Gabon vary widely in digestibility. My observations suggest that mandrills may select items of low toxicity, and that their foraging
strategies and diet may contrast in this respect with the feeding habits of the
chimpanzee. Both mandrills and chimpanzees are large, frugivorous, semiterrestrial
foragers with large home ranges. Hladik [1977] reported a 28% annual proportional
intake of leaves and stems by chimpanzees in terms of fresh weight, as compared to
5% averaged for mandrill stomach contents in the present study.
The mandrill’s digestive system may not be equipped to efficiently process
coarse vegetation such as leaves, bark, and stems. These foods were present in 51%
of the mandrill fecal samples, which suggests that many plants are not fully digestible (Fig. 3). The great diversity of invertebrate species consumed by the mandrills
(Table III) may reflect the mandrill’s need for specific dietary components not
obtainable from vegetable foods.
Although no information is available about mandrill feeding time budgets, the
data presented here indicate that invertebrates of many species (including 14 species
of ants) are regularly eaten. As Hladik [1977] has demonstrated, such insects are
rich sources of amino acids. Chimpanzees in Gabon spent 30-50% of feeding time
foraging for insects. Hamilton et a1 [1978] observed that animal matter is the
preferred food of Papio ursinus, especially when insects are seasonally abundant.
The seasonal fluctuation in availability of foods is probably an important determinant of the diet of mandrills. Redford and Dorea [1984] demonstrated that some
of the most nutritionally valuable insect forms (larvae, alate ants, and termites) are
only seasonally available. Although fruit and insects may require a greater expenditure of time and energy to obtain, the ubiquitous leaves and plant parts may be less
preferred foods owing t o the presence of digestion-inhibiting compounds in green
plants. Vertebrate prey also may be an important, though relatively infrequent,
source of scarce nutrients for mandrills, as has been also suggested for baboons
[Hausfater, 1976; McGrew et al, 1978; Strum, 19801 and chimpanzees [Morris &
Goodall, 19771.
Feeding Behavior and Social Organization
Habitat may be selected for availability of preferred foods and sleeping sites, all
of which, along with other environmental variables and phylogenetic characters,
probably affect the mandrill’s social structure and population dynamics [Lahm,
19851. Although several habitat types were surveyed, the fact that most data collection and observations occurred in forested areas free of very dense undergrowth
24 I Lahm
suggests that mandrills prefer this type of environment, possibly because travel,
visibility of, and contact with group members, and detection of potential predators
are facilitated.
Both home-range and group sizes of mandrills may be dependent on resource
stability. The patchy distribution of fruiting trees in the rainforests of Gabon may
result in the common usage of a large home range by several mandrill groups, which
appear to form larger aggregations on a seasonal basis [Lahm, 19851. If a number of
mandrill groups occupy one large or several smaller overlapping home ranges,
groups may employ different travel patterns to resource sites, thus reducing intergroup competition, as have been suggested for hamadryas baboons [Sigg & Stolba,
19811.
Intratroop competition for abundant, but dispersed foods may be affected by age
or sex-specific dietary preferences [Gautier-Hion, 19801. Although adult male and
female mandrills were observed foraging in trees, smaller group members more
frequently engaged in this activity and were also more likely to climb trees in flight.
Rowel1 119661 observed that immature olive baboons had greater access to
nutritionally rich immature leaves and shoots owing to their greater agility in trees.
If juvenile and subadult mandrills are more easily able to utilize tree leaf materials,
adults may benefit by eating comparatively less toxic plants in the herb layer of the
forest [Waterman, 19841.
Interspecific Competition
Mandrills share their rainforest habitat with a myriad of species, including 120
species of mammals and over 200 species of birds. Competition for food and ecological
niches is mitigated by the evolution of nocturnal and diurnal activity patterns.
Seventy percent of the mammalian species are nocturnal, and 96% of the birds are
diurnal [Charles-Dominique, 19751. Excluding the avian fauna, some of which also
consume fruit, 65 species of mammals, whose diets chiefly comprise fruit, leaves,
stems, flowers, and bark [Emmons et al, 19831, compete with the mandrill for fruit,
its major dietary item.
Differential spatial and temporal utilization of the habitat may decrease competition for resources [Gautier-Hion et al, 19811. The majority of mandrill foods
identified in the present study are found in primary forest, while secondary forest,
riparian, and inundated habitats provide important supplementary foods. Analysis
of the diets of the primates, ruminants, and sciurids of Gabon [Gautier-Hion et al,
19801 revealed that fruit, leaves, and animal matter collectively accounted for 98%
of all ingested food. While over half of the identified fruit species exploited by one
taxonomic group were also exploited by one or more of the other taxa, each taxon’s
general preference for different fruit parts mitigated excessive competition. In general, primates prefer fruit pulp, ruminants swallow small whole fruits, and sciurids
eat seeds.
Of the primates in Gabon, only mandrills, gorillas (Gorilla g. gorilla), and
chimpanzees (Pan t. troglodytes) engage in extensive terrestrial foraging [Emmons
et al, 19831. Although fruits are important food sources for these three species, the
apes are more folivorous than mandrills [Gautier-Hion et al, 19801.
Interspecific competition also may be reduced through choice of alternative foods
during times of environmental periodicity [Hamilton et al, 19781. The mandrill’s
relatively large body size, broad, elongated hands and feet, and enlarged incisors
may offer advantages related to a n increased capability for processing and exploiting
a variety of acceptable foods in both arboreal and terrestrial ecological niches. This
species’ diverse selection of foods within a large supplying area permits the efficient
utilization of a complex environment.
Diet and Habitat Preference of Mandrill / 25
CONCLUSIONS
1. The mandrill diet consists primarily of fruit, supplemented by various other
plant parts, numerous invertebrate species, and occasional vertebrates.
2. The high frequency of insect consumption by mandrills suggests that invertebrates may be highly valued food items.
3. Although mandrills are basically terrestrial, they probably spend a greater
percentage of time foraging in trees than do the Papio species.
4.Mandrills appear to prefer primary forest, but they also forage in secondary,
riparian, and inundated forests.
5. Since mandrills select numerous fruit species within large supplying areas,
they may play a significant role in seed dispersal.
6. Competition for resources in the rainforest is mitigated by species’ preferences
for particular food parts and by differences in spatial and temporal habitat utilization.
ACKNOWLEDGMENTS
I especially thank W.C. McGrew for providing the opportunity for me to pursue
the mandrill field study, and Messrs. Paul Posso and Raphael Dipouma for permission to work in Gabon. The following individuals are gratefully acknowledged for
identification of dietary items: Y. Cambefort, B. Darchen, G. Dubost, D. Faulkner,
F. Feer, A. Hladik, R. Letouzey, and A. Moungazi. Thanks are due to Drs. Clifford
Jolly, Donald Lindburg, and Oliver Ryder for much appreciated constructive criticism of the manuscript, to Sharon Dinwiddie for preparing it for publication, and to
Stephen Nash for permission to use his map of Gabon. I also extend my heartfelt
appreciation to innumerable people in Gabon, France, and San Diego for their
assistance, moral support, warmth, and hospitality during the past 3 years.
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