Geology Reference
In-Depth Information
forest as well. Censuses of the area by S. Stuart
(unpublished data) revealed an average of 2-3
crowned-hawk eagle sighings per day in the
Uzungwas, compared with a rough esimate of
one every 4-5 days reported for Kibale (Sruh-
saker, 198la). All monkey species in the Uzung-
was also gave alarm calls, as well as responding to
the alarms of other primate species, whenever
these eagles were flying overhead. Crowned-hawk
eagles were observed with freshly predated
monkeys on two occasions in the Uzungwas: one
was an adult female Sykes monkey and the other
an unideniied infant (personal observaion).
Pythons, leopards and humans probably predate
these monkeys as well.
in the Easten Arc hat have high atitudinal
ranges comparable to those in the Uzungwas (e.g.
the Nguru and Usambara montane forests) fur-
ther support the above views. Dry season tolerant
plants such as Albizia are absent or at very low
densiies in these other Easten Arc forests
(Lovett, Chapter 4). Red colobus (and
mangabeys) are absent in these forests as well
(Rodgers, 1981), despite the presence of many
plant species in common with the Uzungwas.
These findings suggest that the red colobus (and
mangabey) may have dificuly surviving on much
of the available plant material typically found in
the Eastern Arc. Such a condiion also would have
contributed to the high overlap on primary food
species such as
Albizia
among the Uzungwa
colobines.
Compeiive pressures resuling from high
plant food species overlap among the Uzungwa
colobines probably selected for their divergence at
the plant part level; this point is supported by two
factors. (i) There is extreme specialisaion of the
Uzungwa red colobus on peioles. Peioles com-
prise almost 60% of the red colobus diet in the
Uzungwas (Figure 13.2). They comprise <20%
of the red colobus (Colobus badius tphrosceles) diet
in Kibale; the Kibale red colobus diet is more
evenly spread over peioles, young leaves, and leaf
and flower buds (Struhsaker, 1978). A picture
similar to Kibale is seen among the red colobus
(. b. omitratus) in the riverine forest of Tana
River (Marsh, 1981). The diet of the Zanzibar red
colobus (. b. kirkit) - the closest relaive to . b.
gomorum in the present study (Kingdon, 1981;
Rodgers, 1981; Struhsaker, 198lb) - contains
about one quarter the amount of leaf stems found
in the Uzungwa red colobus diet (Mturi, Chapter
12). Black-and-white colobus are absent from the
Tana forest and Zanzibar Island. (ii) Black-and-
white colobus in the Uzungwas appeared to be
more generalised at the plant part level compared
with black-and-white colobus at Kibale (.
guerza); 56% of the latter species' diet consists of
young leaves compared with less than 20% in the
Uzungwas.
In summary, the potenial for interspeciic
compeiion between the Kibale colobines,
coupled with relaively higher availability of suit-
Biogeographic bases of intespe.ic assoc.ations
Why have the red and the black and white colobines
ailed to om mixed species associations with one
another wherver else thy have been studied
(Sruh-
saker, 1981a)? Plant food species overlap between
the two colobines in the Uzungwas is our imes
greater than that in the well-studied Kibale Forest
(Sruhsaker, 1978). Biogeographic isolaion may
be partly responsible for this high dietary overlap,
resuling in relaively lower availabiliy of suitable
plant food species from which to choose in the
Uzunwas. In fact, the mean dietary overlap
across all monkey species in the Uzungwas is 2.7
imes higher than that mean in Kibale (39.25 vs
15.4, respecively). Virtually all censuses in the
isolated Easten Arc orests have found lower
species diversiies than those ound in the more
vast, coninuously disributed Guineo-Congolian
forests, which includes the species-rich Kibale
(Stuart, 1981; Rodgers et al., 1982; Kingdon,
1989 and several chapters in this volume). In fact,
the majoriy of the main plant food genera in the
diets of the red and the black-and-white col-
obines at Kibale (Struhsaker, 1978) are absent or
at very low densiies in the Uzungwas (Lovett,
Chapter 4); only a few individuals of Ce/tis sp. and
no Markhamia sp. are found in the Uzungwas
(Lovett et al., 1988) - the two most important food
species of the red and the black-and-white col-
obus at Kibale.
Comparisons with other large montane forests
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