Geology Reference
In-Depth Information
mature leaf blade feeding in . b. kirkii was onA.
ummera
and
A. glaberrima.
Moreover, Marsh
all reported that almost 50% of all mature
leaf feeding records for his
. b. rufomitratus
study
group were from Acacia robusta (Burch.). In East
Africa Acacia spp. ypically contain higher con-
centraions of protein in their leaves than most
other genera (Dougall & Drysdale, 1964). The
genus Diospyros generally contains naph-
thoquinone derivaives which are toic to many
groups of animals (Hegenaur, in McKey, 1978).
Species of this genus are generally ignored by red
colobus in Zanzibar; they are weakly selected in
Tana (Marsh, 198la) and Kibale (Struhsaker,
1975), despite their high abundance there. This
genus was also rarely eaten by black-and-white
colobus in Kibale (Oates, 1977), probably for the
same reasons.
The observaion that plant species common in
several field sites were eaten by red colobus in
some areas and ignored in others partly may be
atributable to local variaion in their nutrient and
toins content. It has been demonsrated that the
amount of chemical defence (toins) in plants
against herbivores is influenced by soil ype
(Gartlan, McKey & Waterman, 1978; McKey,
1978). In coastal Cameroun, leached nutrient-
deficient soils are associated with flora showing
exreme chemical defence against herbivores
(Gartlan et al., 1978). An altenaive reason or
the observaion is that differences in abundance
of potenial food sources across ield sites may
afect ood selecivity, causing species to be eaten
in one area but ignored in others.
Monthly and seasonal variaion in species and
item selecion by red colobus could have similar
eplanaions. Concenraions of seconday com-
pounds (chemical defence) may vary in he same
area and plant at diferent imes of day and year
(Huges & Genset, 1973). Other factors such as
abundance of food species and item must also
play a major role in monthly and seasonal vari-
aion in feeding.
All red colobus maintained a diverse diet at
species and item level; the red colobus of Mwani-
hana, which specialises on leaf peioles, is an
excepion (Wasser, this volume).
Plants contain a wide variety of chemical com-
pounds, both nutrients and anifeedants, in
innumerable combinaions of the various plant
parts and species Oanzen, 1978). It may be advan-
tageous, indeed necessary, to diversify the diet in
order to obtain an opimal mix of nurients
(Chivers, 1977; Hladik, 1977; Oates, 1978), and
to take small amounts of a range of anieedants
that may be more tolerated than larger quaniies
of a few (Freeland & Janzen, 1974). Thus, there
may be upper limits at which paricular toins
could be taken without diminishing the net value
of the food eaten. High food species and item
diversity amongst red colobus may enable them to
avoid exceeding the upper limits of paricular tox-
ins that some species and item contain if eaten in
large quantiies. However, high diversity may also
be necessary for a balanced diet. For example, the
red colobus of Mwanihana specialised on leaf
petioles (from several plant species); this plant
part may be phytochemically highly acceptable, as
discussed above, and thus leaf petioles and the
other plant parts may saisy their nutritive
requirements.
The red colobus populaions studied show
variaion in foraging levels. The red colobus of
Zanzibar and Senegal forage at all levels from
ground level to canopy tops; this may be an
attempt to meet their nutrient requirements.
Given the dangers of predaion on the ground
(e.g. python and monitor lizard in Zanzibar) the
nuriional benefits of ground plants must be high.
Black-and-white colobus (Colobus guereza) also
come to the ground, to feed on water plants in
order to obtain minerals (Oates, 1977, 1978).
Other red colobus that forage exclusively above
ground layers (mainly above 10 m), probably get
all their nutrients by so doing.
The red colobus show great similariies in
group composiion, consising of muli-male and
female groups except the Tana red colobus,
whose groups tend to include one or a maimum
of two adult males per group. The presence of
more adult and subadult females than males in
red colobus groups may be explained by the paral-
lel eistence of solitary and/or exra-group males.
It also may be due to higher mortaliy rate in
males. In all red colobus, it is the adult and
subadult males that are mainly involved in
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