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was sighted. At the end of each observation,
observers searched extensively under the feeding
rees for addiional conirmaion of ood types and
especially plant parts eaten. These latter data
were included in the sample only when the speci-
men was obviously fresh, and the exact plant
par/species could not be determined by direct
observaion. Each plant species and part eaten by
a given monkey species during a sighing was
counted only once (i.e. received a count of 1.0,
regardless of the number of individuals per
monkey species observed feeding on it). Diets
(plant food species and parts/species) were cal-
culated for each monkey species by summing
frequency data from (i) direct observations of both
single and mixed species groups, and (ii) collec-
ions found under feeding trees for single monkey
species sighings only. (This latter restricion to
single species sighings served to prevent
erroneous assignment of collected plant parts
eaten when more than one monkey species was
simultaneously feeding in the same tree.) The
duraions of observation/sighing were on average
too brief (mean ±
SE =
22 ± 0.4 min) to allow
calculaions of feeding rates per item of plant
food.
All samples of unknown plant food species
were collected and pressed for subsequent ideni-
icaion. Plant identificaions were made by Jon
Lovett and by the herbarium staff of the Depart-
ment of Botany, University of Dar es Salaam.
matched-pairs signed-rank test (Siegel, 1956)
across months.
Calculation of E is illustrated in equaion 1 for
a comparison of the tendency of red colobus
(R)
to associate with black-and-white colobus (BW)
versus with mangabeys
(M).
The epected
frequency of
R
associating with BW in this com-
parison (E8w) was calculated as the proportion of
the total BW sighings (BW
TOT
=
freq. single
+
freq. mixed species sighings of BW) among the
total number of BW and
M
sighings [BW
TOT +
M
T
o
T
- (freq. mixed sighings of BW and
M)]
over each one-month block, muliplied by the
total number of mixed group sighings between
R
and BW and
R
and
M
in that month:
E8w
=
BW
TOT/
(
BW TOT +
M
TOT
- BW
& M
M1xw
)
(1)
X
[R&
BWMIXEo+
R&M
MIXED]
A comparable
EM
was calculated for mangabeys
by subsituing
M
T
o
T
for BW
TOT
in the numer-
ator of equaion 1. Each expected frequency (£)
was then subracted rom its respective observed
frequency
(0)
in that month to obtain the 'nor-
malised' values
(0
- ) compared in the
Wilcoxon matched-pairs signed-rank test.
Similarly, equation 2 shows the expected value
for
R
to associate in single
(R
s
)
versus mixed
species groups with BW:
E
R=
R
TOT/
(
BW TOT+
R
T
o
T -
R &
BW
MIXED
)
(2)
E8w in the second comparison was obtained by
subsituing
BWT
o
T
for
R
T
o
T
in the numerator,
and BWs for
R
s
in equaion
2.
Dietary overlap was calculated by summing the
percentages of each food species (or part/food
species) in the diet of primate species
i
that was
shared by primate species j in a given month
(Struhsaker, 1978).
Anayses
Observaion time varied in this study across
primate species as well as by month, based on
their availabilities in the study area. Availability of
different plant parts/species also varied monthly.
For these reasons, all data were summarised in
one-month blocks. Associaion frequencies were
compared across months after normalising associ-
ation data around the monthly availabilities of
each monkey species in the comparison; observed
(0)
association frequency data were subtracted
from expected () associaion frequencies, where
E was based on the availabilities of each species
during that month. These
(0
- E) differences
then were compared using the Wilcoxon
Results
The red colobus and black-and-white colobus
were most heavily concentrated at elevaions
between
400
and
1000
m. Sykes monkeys
appeared to be evenly distributed at all elevaions,
whereas mangabeys were more heavily con-
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