Fracture Toughness of Mountain Gorilla (Gorilla gorilla beringei ) Food Plants
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American Journal of Primatology 62:275–285 (2004)
RESEARCH ARTICLE
Fracture Toughness of Mountain Gorilla (Gorilla gorilla
beringei ) Food Plants
ALISON ELGART-BERRY*
Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York
Mountain gorillas, the largest extant primates, subsist almost entirely on
plant matter. Moreover, their diet includes a substantial amount of
structural material, such as bark and stems, which other primates tend to
avoid. Accordingly, the robust masticatory apparatus of gorillas may be
adaptive to this presumably tough diet; however, quantitative informa-
tion on this subject is lacking. In this study the fracture toughness of
mountain gorilla foods was examined for the first time. Samples of 44
food plants from Bwindi-Impenetrable National Park (BINP) and
Mgahinga Gorilla National Park (MGNP) were tested. These parks are
inhabited by two gorilla populations that regarded by some as being
distinct at the subspecific taxonomic level. Although food toughness did
not differ between the two populations, both diets contained tough items.
Tree barks were the toughest food items (varying from 0.23 to 8.2 kJ/m2),
followed by shrub barks, pith, and stems. The toughness of leaves and
fruit was negligible compared to that of bark. The toughness of bamboo
was low in comparison to the toughest food items. Accordingly, the
prominent toughness of bark, pith, and stems may be key factors in the
evolution of orofacial robusticity in mountain gorillas. Am. J. Primatol.
62:275–285, 2004. r 2004 Wiley-Liss, Inc.
Key words: mountain gorilla; Bwindi-Impenetrable National Park;
Mgahinga Gorilla National Park; fracture toughness
INTRODUCTION
The diet of the gorilla (Gorilla gorilla Savage and Wyman), particularly the
mountain gorilla (G. g. beringei Matschie), appears to consist of very hard, tough
items. Because the dentition of a mammal is adapted to its diet [Lucas, 1979,
1991, 1994; Fortelius, 1985; Lucas et al., 1986; Lucas & Corlett, 1991; Strait,
1993; Lucas & Teaford, 1994; Hill & Lucas, 1996; Strait, 1997], it is presumed
Contract grant sponsor: Mario Einaudi Center, Contract grant sponsor: Kosciusko Foundation;
Contract grant sponsor: Human Biology Program at Cornell.
*Correspondence to: Alison Elgart-Berry, 517 NE 38th St., Miami, FL 33137. E-mail: ae16@att.net
Received 28 February 2003; revision accepted 6 December 2003
DOI: 10.1002/ajp.20021
Published online in Wiley InterScience (www.interscience.wiley.com).
r 2004 Wiley-Liss, Inc.276 Elgart-Berry
that gorillas possess large jaws and teeth in order to process mechanically
resistant foods [Schaller, 1963; Groves, 1966; Cousins, 1988; Taylor, 2002].
However, the mechanical properties of these foods have never been measured.
Gorillas and other herbivores possess dental cusps that specialize in
fracturing cell walls in order to gain access to the nutritive cellular contents
[Janis & Fortelius, 1988]. The study of fracture mechanics of foodstuffs allows
one to examine the food–tooth interface of any type of food [Lucas, 1994; Strait,
1997]. Measurements of fracture toughness, which is defined as ‘‘the work
required to fracture a unit area of tissue’’ [Lucas & Teaford, 1994:183], allow all
foodstuffs to be directly compared.
This study represents the first attempt to measure the fracture toughness of
mountain gorilla foods. Two gorilla populations in Uganda, in Bwindi and
Mgahinga (in the Virungas), were studied. Sarmiento and colleagues [1996]
argued that the gorillas that inhabit the Bwindi forest are not true mountain
gorillas. They based their argument partially on dietary differences, and noted
that the Virunga population has a more ‘‘herbaceous’’ diet than the Bwindi
gorillas, which creates an adaptive regime for a more robust masticatory
apparatus. In the current study, the diets of both populations were assessed,
and plant parts such as bark, leaves, pith, stems, and fruit were tested at both
field sites.
MATERIALS AND METHODS
Study Groups
Mountain gorilla foods were tested in two national parks in Uganda: the
Bwindi-Impenetrable National Park (BINP), located in the Kigezi Highlands of
southwestern Uganda, and the Mgahinga Gorilla National Park (MGNP), located
in the Virunga Volcanoes (Fig. 1). Fieldwork in BINP was based at the Institute
for Tropical Forest Conservation (ITFC). The park reserve, which ranges in
elevation from 1,190 to 2,607 m, is characterized as both a medium-altitude moist
evergreen forest and a high-altitude forest [Howard, 1991]. There were 11 gorilla
groups in BINP in 1998, comprising about 350 individuals [Achoka, 1993]
(unpublished Bwindi census, 1997), and most researchers refer to them as
subspecies G. g. beringei [e.g., Emlen & Schaller, 1960; Schaller, 1963; Groves &
Stott, 1979; Harcourt, 1981; Butynski, unpublished survey].
In this study, it was assumed that the physical properties of the preferred
plant foods would have the greatest impact on gorilla dentition. These plants were
identified from ITFC records, interviews with ITFC personnel, and personal
observations. ITFC records indicate that the Bwindi gorilla diet consists of 52%
leaves, 30% bark, 9% fruit, 9% pith and stems, 0.5% rotten wood, and 0.1% roots.
Bark and stems comprise more of the diet than was reported by Sarmiento and
colleagues [1996] (o10%). The fracture toughness of 10 species of bark, six
species of fruits, 14 species of leaves, and seven species of pith were tested at
BINP. Most items that formed 41% of the Kyagurilo gorilla group (BINP) diet
were tested (Table I).
The forests of BINP and MGNP (which is located 25 km south of BINP) were
continuous until approximately 500 years ago, when human cultivation separated
them. The forest of the Virunga Volcanoes is an afro-montane humid forest
[Vedder, 1984] ranging in altitude from 2,600 to 4,507 m [Plumptre & Harris,
1995]. The Virunga gorillas have been the focus of most mountain gorilla studies
[e.g., Fossey & Harcourt, 1977; Fossey, 1983; Vedder, 1984; Watts, 1984;
Plumptre & Harris, 1995].Toughness in Gorilla Food Plants 277
Fig. 1. Location of BINP and MGNP in southwest Uganda.
The Nyakagezi group, which inhabits the lower regions of Mt. Gahinga and
Mt. Sabinio (G. Myooba, personal communication), was visited and feeding bouts
were videotaped. Data from personal observations, interviews with rangers
working at Mgahinga, and past studies indicate that five species of plants
(bamboo (Arundinaria alpina), Galium ruwenzoriensis, Carduus nyassanus,
Laportea alatipes, Rubus sp., and Peucedanum linderi) are the top-ranking food
plants in the Virungas [Schaller, 1963; Fossey & Harcourt, 1977; Fossey, 1983;
Watts, 1984; Vedder, 1984]. All of the mountain gorilla staples except Laportea, as
well as nine other species that were eaten by the Nyakagezi group, were tested
(Table I). The ‘‘Virunga’’ diet consists of approximately 60–65% leaves, 23.3%
stems and roots, 6.9% wood, 1.7% fruit, and 2.3% flowers. Of the favored food
plants tested at MGNP, three were tree bark, one was a root, two were pith, three
were stems, nine were leaves, one was an entire plant, and one was a fungus
(Table I).
Testing Apparatus
A portable, durable, and inexpensive apparatus to test the food was
assembled from commercially available parts. All food samples were tested
within 24 hr after collection to avoid changes in texture [Lucas et al., 1994;278 Elgart-Berry TABLE I. Dietary frequency and fracture toughness of each plant species by plant part and by park (BINP or MGNP). Dietary Frequency Plant species Habit/part tested n R (kJ/m2) x (SD) BINP Bark 0.3 Ficus natalensis Tree 6 5.98 (2.63) ? Eucalyptus sp. Tree 6 5.43 (2.16) 3.5 Piper capensis Shrub 6 4.83 (2.11) 3.9 Ipomea sp. Climbing herb 6 4.56 (1.03) 2.5 Myrianthus hoestii Tree 6 2.81 (0.70) ? Lapene sp. Tree 5 2.76 (1.11) 0.2 Maytenus acuminata Tree 6 0.66 (0.52) 1.0 Triumfetta macrophylla Woody herb 7 0.62 (0.40) 7.6 Urera hyselodendron Shrub 6 0.49 (0.28) ? Dombeya goetzenii Tree 6 0.26 (0.12) 10 Mimulopsis sp. Herby shrub 6 0.23 (0.06) MGNP bark/root ~0.7 Vernonia adolphi-frederici Woody herb 2 1.37 (0.25) ? Kniphofia thomsonii Herb root 5 0.93 (0.68) ? Dombeya sp. Tree 6 0.89 (0.21) ~6.79 Arundinaria alpina Grass 7 0.19 (0.14) BINP pith/stem/fungus 3.5 Piper capensis Shrub pith 7 4.05 (2.48) ? Tridium sp. Fern pith 6 1.30 (0.77) ? Ensete sp. (Wild Banana) Herby tree pith 7 1.20 (0.27) 1.8 Ganoderma australe Bracket fungus 10 0.17 (0.09) 3.9 Brillantasia sp. Shrub pith 6 0.10 (0.03) 0.3 Vernonia sp. Woody herb pith 6 0.05 (0.01) MGNP pith/stem/fungus ? Cynoglossum geometricum Herb stem 3 3.86 (1.53) B0.7 Vernonia adolphi- frederici Woody herb pith 3 2.59 (1.26) B9.4 Carduus afromontanis Herb stem 6 1.91 (0.56) B0.1 Rumex ruwenzoriensis Herb stem 5 1.26 (0.44) B1–20 Galium ruwenzoriensis Herb stem 5 0.51 (0.25) B1–10 Peucedanum linderi Herb stem 4 0.27 (0.16) B1–10 Peucedanum linderi Herb petiole 4 0.18 (0.03) ? Engleromyces goetzii Fungus 6 0.07 (0.02) Fruits ? Olinia usambarensis BINP tree 6 1.19 (1.52) 1.8 Myrianthus hoestii BINP tree 8 1.18 (0.45) 0.3 Xymalos monospora BINP tree 5 0.71 (0.22) 5.0 Chrysophyllum albidum BINP tree 6 0.07 (0.03) 3.6 Rubus rigidus Shrub 6 0.02 (0.03) BINP Leaf 2.5 Myrianthus hoestii Tree 6 1.19 (0.57) ? Unknown species Herb 6 0.21 (0.11) 2.0 Olea sp. Tree 6 0.13 (0.02) 7.0 Triumfetta macrophylla Woody herb 7 0.11 (0.04) 0.3 Xymalos monospora Tree 7 0.11 (0.04) 8.0 Momordica sp. Herb 6 0.06 (0.01) 5.0 Urera hyselodendron Shrub 6 0.06 (0.02) 3.5 Ipomea sp. Herb 6 0.06 (0.02) 8.0 Mimulopsis sp. Herb shrub 6 0.05 (0.01) 0.3 Vernonia sp. Woody herb 6 0.04 (0.02) 3.8 Basella alba Herb 6 0.03 (0.01) 3.6 Rubus rigidus Shrub 6 0.02 (0.01)
Toughness in Gorilla Food Plants 279
TABLE I. (Continued)
Dietary Frequency Plant species Habit/part tested n R (kJ/m2) x (SD)
MGNP leaf
B0.2 Vernonia adolphi- frederici Woody herb 2 1.33 (0.49)
B0.4 Lobelia lanurensis Herb 5 1.03 (0.88)
B0.1 Rumex ruwenzoriensis Herb 3 0.52 (0.08)
B1–20 Galium ruwenzoriensis Herb 5 0.51 (0.25)
0.4–22 Carduus afromontanis Herb 3 0.49 (0.26)
? Cluytia abyssinica Herb 5 0.46 (0.09)
? Cynoglossum geometricum Herb 3 0.37 (0.06)
? Noxia congesta Herb 5 0.32 (0.14)
? Discopodium penninerve Shrub 5 0.31 (0.06)
? Mimulopsis sp. Herby shrub flowers 6 0.06 (0.01)
Listed in order of maximum toughness to minimum toughness in each food category.
M. Bourne, personal communication, 1996]. A Shimpo 20-kg force gauge was
mounted on a Chatillon test stand. Attached to the force gauge was a wedged test
piece [sensu stricto Lucas & Teaford, 1994] that sheared against a circular hole in
a custom-designed test plate, creating a type II mode of fracture.
Plant sections were tested after the samples were cut to an equal thickness of
2 mm, because the toughness of thinner specimens is often thickness-dependent
[Vincent, 1990; Lucas et al., 1995]. If leaves or bark were significantly thinner
than 2 mm, the specimen was tested singly and pieces were grouped until the
desired thickness was achieved. The source of error from testing multiple pieces
was considered in the results. Six trials were run on each plant part, and
the results of the tests varied in toughness. The toughest part of the plant that the
gorillas would have consumed (e.g., the leaf mid vein) was tested to obtain the
potentially maximum values for toughness [Lucas et al., 1991].
The sample was placed between a plexiglass cover and the base plate of the
test plate, and the test piece was lowered onto it at a timed rate. An assistant
controlled the speed of the crosshead displacement by turning the hand wheel at
0.065 mm/sec. The crosshead displaced 2–3.75 mm at a rate of 3.9 mm/min. A slow
crosshead speed increases the sensitivity to differences in the fracture property of
materials [Evans & Sanson, 1998].
After the sample was loaded, crack propagation ensued. The sample was then
unloaded to ensure that the measurement of work done in the test did not include
stored elastic strain energy [Vincent, 1990]. A second pass was made with the
fractured sample in place to account for friction. The raw data, which consisted of
a force reading in Newtons every 2 sec, were transformed into two force-
displacement curves. The areas beneath the force-distance curve of the first pass,
which is the total apparent work-of-fracture (W1), and that beneath the curve of
the second pass, which is the work-of-friction (W2), were integrated by means of
the program Kaleidograph (Abelbeck Software). The work-of-friction was
subtracted from the total work (W1) to obtain the true work-of-fracture [Lucas
& Pereira, 1990; Darvell et al., 1996], and fracture toughness, R, was calculated
by the following equation:
R ¼ ðW1 W2 Þ=lt
where l is the length of the test piece cut (the perimeter of the punch), and t is the
thickness (both of which were measured with digital calipers). Fracture toughness
was calculated for each plant part, in Excel (Microsoft), and reported as kilojoules
per square meter (kJ/m2), which is the standard unit for fracture toughness.280 Elgart-Berry
The means and standard deviations for fracture toughness were calculated
for each plant species tested and for each plant part (e.g., bark) at BINP and
MGNP. An analysis of variance (ANOVA) was used to test the variance in the
fracture toughness of all plants eaten at BINP vs. MGNP. Each trial was treated
as a sample. Scheffe’s and Games/Howell post hoc tests were used to extract
which plant group means (for example, the BINP bark mean compared to the
MGNP bark mean) were significantly different. Wilcoxon rank-sum tests were
also run, since the data may not have been normally distributed.
RESULTS
The fracture-toughness values of all plants tested are shown graphically in
Fig. 2 as a box-and-whiskers plot, and are listed in Table I. The toughest food
plants were tree barks eaten at BINP. Ficus natalensis, Piper capensis, Ipomea
sp., and Eucalyptus sp. barks have fracture toughness values 44.5 kJ/m2
Fig. 2. Box-and-whiskers plots with equal scales for bark, pith, and stems, but different plots for
leaves, showing fracture toughness (R) values. Each box encloses 50% of the data around the
median, which is displayed as a line. The ‘‘whiskers’’ mark725% of the data. A: BINP and MGNP
fracture toughness of bark by plant genus. B: BINP and MGNP fracture toughness of pith, stems,
and fungi by plant genus. C: BINP and MGNP leaf fracture toughness by plant genus. Note the Y-
scale. D: The summary of fracture toughness (R) values for bark, pith and stems, and leaves for the
two populations.Toughness in Gorilla Food Plants 281
(Table I, Fig. 2A). Not all are eaten frequently, but Piper capensis constitutes
approximately 2.5% of the studied BINP group diet. Shrub barks, which have far
lower toughness values than tree barks, constitute larger portions of the BINP
diet. The most commonly eaten food item (accounting for about 10% of the diet) is
Mimulopsis sp., which is also the least tough bark (mean fracture toughness =
0.23 70.06 kJ/m2). Urera hypselodendron, another dietary staple (constituting
7.6% of the diet), also has a low toughness value. Far less bark was tested at
MGNP compared to BINP due to the lesser importance of trees and shrubs in the
MGNP gorilla diet; however, the results indicate that the mean fracture
toughness of MGNP bark is considerably lower than that of BINP bark (Fig.
2A and D). The fracture toughness of bamboo (Arundinaria alpina) is low, at
0.270.1 kJ/m2. The mean fracture toughness for BINP and MGNP bark is
2.2275.6 kJ/m2 and 0.772.7 kJ/m2, respectively.
The fracture toughness of piths, stems, and woody fungi is lower than that of
bark (Fig. 2B). The highest toughness value was found in Piper capensis (4.05 kJ/
m2) at BINP, and in Cynoglossum geometricum (3.86 kJ/m2) at MGNP. Carduus
aftromontanis, one of the staple mountain gorilla foods, is moderately tough (Fig.
2B). Overall, the mean for pith/stems/fungi at BINP and MGNP was 0.5470.43
kJ/m2 and 1.1171.66 kJ/m2, respectively.
Leaves had low toughness values relative to other food categories (Fig. 2C).
Aside from one tough leaf (Myrianthus hoestii, the giant gooseberry tree; R = 1.19
kJ/m2) eaten at BINP, the toughest leaves are consumed at MGNP. Preferred
foods, such as Carduus afromontanis and Rumex ruwenzoriensis, possess fairly
tough leaves. When I observed the Nyakagezi group, they were feeding
predominantly on Mimulopsis flowers, which are very low in toughness (Fig.
2C). Vernonia and Lobelia leaves had high toughness values, as expected from
their large size. A regression determined that a significant (Po0.001) positive
correlation exists between leaf area and toughness, which agrees with the results
of Lucas and colleagues [Lucas et al., 1995, 1997].
The five species of fruit tested had moderate toughness values. Chrysophyl-
lum sp. fruits are very soft and low in toughness, while Olinia usambarensis and
Myrianthus hoestii fruits are tougher. Very low toughness Rubus sp. (wild
raspberry) fruits are eaten in both parks. In addition to these fruits, other types of
fruits are also eaten at BINP, but they were not fruiting during the months this
study took place. However, the untested fruits have little relevance in the BINP
diet (Table I).
The results from Student’s t-tests of interpopulation comparisons of plant
types (e.g., bark) were all significant. For example, the t-tests revealed that the
leaves tested at MGNP are tougher than those tested at BINP (Table II).
However, the use of multiple t-tests increases the probability of a Type I error.
The ANOVA test on the difference in fracture toughness between BINP and
MGNP food plants, by type (omitting fruit), revealed that there is a significant
variation in fracture toughness values (P = 0.0098, Table II). However, variation
of fracture toughness within the BINP and MGNP leaves tested exceeds variation
between those populations, and post-hoc tests revealed that most of the
significant pairwise comparisons were not pairings of one plant part between
populations. The post-hoc tests (Fisher’s PLSD, Scheffé’s, and Games/Howell) did
not confirm the results of two of the t-tests. The multiple-comparisons tests
indicated that no significant difference exists in either leaf fracture toughness
means or pith and stem fracture toughness means between populations. However,
the post-hoc tests confirmed that BINP bark is significantly tougher than MGNP
bark (Table II). Other significant pairwise comparisons are given in Table II.282 Elgart-Berry
TABLE II. Results of ANOVA, R Means for Each Category, and Results of t-tests ANOVA table
for fracture toughness of BINP v. MGNP food plants
Source of variation DF Sum of squares Mean square F-value P-value
Between
groups 1 18.8 18.8 6.8 0.0098
Within
groups 311 864.6 2.82.1
Results of t-tests and ANOVA post-hoc Tests
BINP-MGNP Bark Pith/stems Leaves
t-test P-value (2-tail) o0.00001 0.03 0.0009
Fisher’s mean diff. 2.0 0.2 0.2
Fisher’s critical diff. 0.7 0.7 0.6
Fisher’s P-value o0.0001 0.6 0.4
Scheffe mean diff. 2.0 0.2 0.2
Scheffe crit. diff. 1.3 1.2 1.0
Scheffe P-value o0.0001 0.99 0.99
Other significant post-hoc pairwise comparisons, Fisher’s PLSD
Comparison Mean diff. Critical diff. P-value
BINP bark-pith/stem 1.7 0.6 o0.0001
BINP bark-MGNP pith 1.5 0.6 o0.0001
BINP bark-leaf 2.5 0.5 o0.0001
BINP bark-MGNP leaf 2.3 0.6 o0.0001
BINP pith-leaf 0.8 0.6 0.005
MGNP pith-BINP leaf 1.0 0.6 0.0009
MGNP pith-leaf 0.8 0.7 0.02
Most of these comparisons indicate significant differences in the means between
bark and leaf fracture toughness, or between pith and leaf fracture toughness.
The results of the Wilcoxon rank-sum tests indicate significant Z-scores between
BINP and MGNP bark (Po0.01) and between the leaves of the two populations
(Po0.01), but the score for the piths is not significant.
The dietary frequency of plant items was compared with their toughness
values, but no correlation was found. The overall toughness of the BINP diet was
compared with that of the MGNP diet by several of the above-mentioned
methods. Not accounting for dietary frequencies, BINP food is significantly
tougher (R = 1.2 kJ/m2, P = 0.01) than MGNP food (R = 0.7 kJ/m2); however,
there were twice as many samples for BINP as for MGNP.
DISCUSSION
Bark was the toughest plant part tested, followed by stems, fruit, and leaves.
Most leaves and fruit have negligible toughness values when compared to bark
and pith values. Trees have the toughest bark, whereas shrub barks are low in
toughness. The fracture toughness values calculated here are similar to published
values regarding toughness of wood and leaves [Ashby et al., 1995; Lucas &
Corlett, 1991]. Lucas et al. [1995] found that toughness varies with the density of
the tissue or volume fraction that the cell wall occupies. The type of cell geometryToughness in Gorilla Food Plants 283
in a plant, and the plant’s thickness are also factors that affect fracture toughness
values.
Of the bark tested, the bark eaten by gorillas at BINP (constituting 30% of
the diet) is significantly tougher than the bark eaten at MGNP (6.9% of diet). The
barks that are frequently eaten in both parks are mostly shrub species and are
low in toughness. Whether toughness is a factor in the selection of these species
over others as food was not addressed in this study. Information on plant density
at BINP was not available at the time of this study; however, a study on this
subject is under way.
The five top-ranking foods of the mountain gorillas were low to moderately
tough (o1.92 kJ/m2). Bamboo (Arundinaria alpina) shoots eaten by Virunga
gorillas have low toughness values (0.270.1 kJ/m2), which counters the
hypothesis that bamboo is a selective regime to which the gorillas are adapting
[Schaller, 1963; Groves, 1971; Cousins, 1988]. The bamboo shoots tested here,
which showed clear evidence of mastication, were new shoots and were not woody
in consistency. Clearly, large body size should not be viewed as a prerequisite to
eating bamboo, as it has been in the past [e.g., Schaller, 1963; Groves, 1971;
Cousins, 1988]. The eastern chimpanzee (Pan t. troglodytes) [Casimir, 1975] and
the bamboo lemur (Hapalemur griseus), which are considerably smaller than the
gorilla, both consume bamboo. Seligsohn and Szalay [1978] determined that
the puncture-crushing of the dentition was the key adaptive feature for
consuming bamboo in Hapalemur. They concluded that the rigidity and width
of the stem are the variables that create a selective regime; however, they never
tested toughness.
The pith and stems eaten at MGNP, where they constitute approximately
23% of the diet, are tougher than those eaten at BINP, where they constitute only
9% of the diet. Three rather tough stems (Cynoglossum lanceolatum, Vernonia
adolph-frederici, and Carduus afromontanis; R = 2–6 kJ/m2) are commonly eaten
at MGNP.
Leaves, the most frequently eaten plant item, also have the lowest toughness
values. Leaves account for approximately 60–65% and 52% of the diet at
MGNP and BINP, respectively, and are both larger and significantly tougher at
MGNP.
The overall toughness of the BINP and MGNP diets cannot be fully
compared because knowledge regarding the dietary frequency is limited.
However, an ANOVA and multiple-comparison tests did not indicate significant
differences in the overall toughness of the diets between the two populations.
Accordingly, these results do not support the suggestion that Virunga gorillas
consume a bulkier, more herbaceous diet than Bwindi gorillas and thus endure
higher masticatory stresses [Sarmiento et al., 1996]. Therefore, on the basis of
dietary differences alone, these two populations should not be differentiated at
the subspecific level.
ACKNOWLEDGMENTS
This work was done in conjunction with the ITFC and the Uganda Wildlife
Authority. Dr. Richard Malenky, Simon Jennings, Maryke Gray, Nancy
Thomson-Handler, and Godfrey Mayooba provided assistance in the field. Dr.
Peter Lucas of Hong Kong University, and Dr. Malcolm Bourne of Cornell
University provided me with much needed information about the testing of
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