Geology Reference
In-Depth Information
Table 12.6. Food item diversity indices in two studies of red colobus
Zanzibar (this study)
Kibale
(Struhsaker, 1975)
Group CW
l.93 b
2.32 b
2.25 b
2.35
2.32
2.31
l.95 a
2.3z b
2.50 a
2.18 b
2.20 a
2.35 b
2.18 b
2Jl c
2.48 b
l.88 c
2.03 b
2.13 c
2.21
Month
Group I
Group II
Group III
l.55 d
1.89 d
April
May
1.49
1.40
June
1.23
1.43
July
1.48
1.37
l.09 d
1.32
1.31
August
1.35
1.64
1.61
September
1.81
October
1.54
1.17
November
1.58
0.98
0.91
December
1.38
1.41
1.31
1.17 '
1.01 '
1.12 '
January
February
1.35
1.23
1.26
March
1.66
1.68
1.18
Average
1.47
1.40
1.19
Note: a l 970; b l 971; c l 972; d l 980; ' l 981.
accurately it isa better guide to the relaive size of
canopy than use of canopy index, which is
esimated. Several studies have used canopy index
in calculaing selecion raio (Struhsaker, 1975;
Marsh, 1978a, 198 la); however, the use of basal
area is becoming more popular (Waterman &
Choo, 1981; McKey et al., 1981; Bennett, 1983).
Selecion raio serves as an approimate indicator
of the diferenial use of species in relaion to
their abundance and thus helps to explain the
diferences between species in their conribuion
to the diet.
The Zanzibar red colobus preferred some plant
species more than would be epected rom their
abundance: these had high selecion raios and
ranks. Other species were eaten less than expec-
ted from their abundance: these had low selecion
raios and ranks (Table 12.1). Similar observa-
ions have been made for Tana, Kibale and
Gombe red colobus (respecively, Marsh, 1978a,
1981a; Struhsaker, 1975; Clutton-Brock, 1975a).
However, the three studies used different form-
ulae in calculaing selecion raios, which limits
direct comparison.
Selecion or plant part was invesigated relat-
ing its contribuion to diet and its abundance
index (An) from phenological measures. Spear-
man rank correlaion coeficients or six items
over 12 months were calculated. Variaion of the
proporion in the diet for young leaves, unripe
fruits and mature leaves did not correlate signifi-
cantly with the abundance of these items in the
canopy. A significant correlaion was ound or
leaf buds (rs
0.608, P < 0.05; rs
0.566,
=
=
P < 0.05), ripe fruits (rs
0.618, P < 0.05;
=
0.651, P < 0.05) and flower and floral buds
(rs = 0.574, P < 0.05; rs = 0.695, P < 0.05), for
groups I and II, respecively. Marsh (198la)
observed that variaion in the proporion of fruit,
flowers and leaf buds in the monthly diet did not
rs
=
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