Mammals in the forests of eastern africa - Biogeography and Ecology of the Rain Forests of Eastern Africa - page 238

history. Similar consideraions could explain the
stranding of . cosensi on Zanzibar while . emini
is now ied to the main forest block. Both emini
and cosensi are capable of behaving like gambianus
in that they will invade villages, towns and culiva-
ion within their habitat. The ecological and adap-
ive success of . ga mbianus may therefore be the
single most important factor in limiing the dis-
tribuion of . emini and possibly Beamys. Both
may be inrinsically less exclusive forest mammals
than they appear and this could apply to other
easten endemics.
Red duikers are common in most African forest
areas. In Tanzania, the larger Cphalophus haoyi
has a predominantly northen and central dis-
tribuion, while . natalensis occurs in the south.
Intermediate forms, which may be hybrids, are
known from what could be an overlap zone run-
ning inland from the general vicinity of Dar es
Salaam. An equivalent niche in the rich lowland
orests of Uganda is occupied by the substanially
larger . calipygus. In Kenya presumed hybrids
between . callipygus and . haoyi have been
collected along the zone of contact on the easten
face of the Mau.
Equatorial montane habitats from Cameroun to
Mount Kenya are inhabited by the long-legged,
long-hooved . nigrirons. This species prefers
boggy, wet areas within the high rainfall belts.
Equivalent habitats in Tanzania are occupied by
the less specialised . haoyi. It is a typical pat-
tern that there are more specialisaions and more
species in the Guineo-Congolian forests while
the east possesses fewer species of greater adapta-
bility and a broader ecological range.
A group that typifies endemism along the lit-
toral and in the mountains of easten Africa is the
Fu nisiurus paliatus/lucier complex of squirrels. A
succession of discretely differing populaions of F.
palliatus is strung down the coast from Somalia to
Zululand. On the mountain massifs inland there
is a variety of mountain squirrels, which one of us
has united into a single species, F. lucifer (King-
don, 1974b). A more advanced and successful
species of squirrel, Heliosciurus uo brachium, is
the only medium-sized tree squirrel in the drier
surrounding woodlands but is sympatric with
Fu nisciurus types in the richer and more diversi-

fied forests further west (except at higher
alitudes). Fu nisciurus is presumably competiively
inferior in dry woodland today, but was it always
unable to cross dry woodland? Alternaively, could
the arrival of Heliosciuus have inhibited it?
Subsequent isolation of the mountain squirrel
complex has been sufficiently lengthy to have led
to differentiaion into at least ive disinct forms
living on some 12 mountain massifs. In a single
small locality on the West Usambaras there is a
very small population of a unique species, F. vexil-
larius. One of us (Kingdon, 1974b) has suggested
that this squirrel could be a hybrid swarm derived
from miing between . lucifer byatti and F. pal-
liatus but the populaion appears to be monomor-
phic and so may represent an independent
offshoot from the F. lucer complex. Compeiion
is but one factor restricing such endemics to
montane areas. Condiions have undoubtedly
been more benign but also more severe in the
past. Today's forest patches and galleries may be
vesiges oflarger areas that eisted in the past and
the core of their habitats may or may not have
remained relaively stable, but their proimity to
much drier environments would always have been
closer than in most westen forests.
Mammal groups probably vary greatly in their
responses to geographic isolaion, ragmentaion
of populaions, ecological constricion or com-
munity impoverishment. A smaller choice of food
plants may force one species to become more spe-
cialised in its diet while fewer potenial com-
peitors allow another to broaden its niche. A
species prone to colour variaion (such as the
squirrels and the giant elephant shrews) will more
readily generate regional varieies or subspecies
through isolaion than a less variable one.
Where eastern and westen populaions of the
same species can be compared it may be worth
tesing these aspects of their environment to see if
the survival of more versaile ypes has been
favoured in the east. If some forest species have
been recruited from non-forest populaions it will
be interesing to determine to what extent they
could have lost their tolerance for relaively dry
condiions, whether their restricion is primarily
attributable to compeiive exclusion in more dif-
ficult habitats, or both. It is possible that westen