Geology Reference
In-Depth Information
Table 4.8.
Examps of genera with enemic sp ecies
in the Eastn Arc which app ear to be neoendemics
pavolia;
and the montane and lowland forest
Eastern Arc endemic
Is oberlinia schfiei
has
longer pedicels than the widespread and variable
woodland /.
angolensis.
.
schfieri
is one of the few
examples of a woodland genus also occurring in
the moist forests. Otherwise the forests are
lorisically very disinct from the surrounding
woodlands.
Number of
Number of
Number
Eastern Arc
Eastern Arc
of species
endemics
worldwide
Genus
species
19
17
320
Memeylon
10
7
15
Stolzia
36
17
200
Polystaclzya
29
20
400
Pavetta
Discussion
9
8
90
Coea
In comparison to moist forests in Malawi to the
south and central Kenya to the north, Easten Arc
forests are excepionally rich in endemic species.
For example, Malawi has only ten endemic moist
forest ree species (Dowsett-Lemaire, 1989,
1990) and central Kenya only eight (Beentje,
1988b) in comparison to 67 Easten Arc
endemics. The South African Cape forests,
unlike other Cape vegetaion types, have few spe-
cies or genera of restricted distribuion. Other
parts of Africa where there are many moist forest
species of restricted distribuion are the high rain-
fall areas of Cameroun, Gabon and Zaire; and the
easten side of the Kivu-Rwenzori mountains.
The richness of these centres of endemism has
been ascribed to moist forest survival in areas of
high rainfall during proposed Pleistocene
droughts (Hamilton, 1976, 1982). Certainly the
Eastern Arc cannot have suffered a major loss of
forest or a substanial lowering in altitude of forest
types in the last 30 000 years, or the range of
endemics in different forest types apd of different
ainiies would not be present today. This bio-
logical evidence is supported by evidence from
deep-sea drilling which indicates that Indian
Ocean surface temperatures off the coast of trop-
ical eastern Africa did not decrease substanially
during the last glacial maimum (Prell
et a. ,
1980;
van Campo
et al. ,
1990) and hence that rainfall
would have been similar to that at present.
Although evidence or dramaic climaic changes
during the Pleistocene is strong (Hamilton, 1982)
it is possible that they were limited to certain
areas. For example, southeast Zaire, Angola,
northwestern Zambia and southwesten Tanzania
make up an area of excepional species richness
and endemism in a woodland and riverine forest
42
28
500
Psyclzotria
11
10
150
Lasiantlzus
38
27
900
Impatiens
20
20
21
Saintpaulia
18
13
130
Strptocarpus
6
6
7
Zimmemannia
Source:
From Bridson & Verdcourt,
1988;
Cribb,
1984;
Grey-Wilson,
1980;
Hilliard & Burtt,
1971;
Johansson,
1978;
Smith,
1987;
Verdcourt,
1976;
Wickens,
1975.
more widespread forest edge or woodland spe-
cies. For example the small pink-flowered
southen Uzungwa shrub
Bersama rosea
probably
arose from the widespread, variable montane for-
est and forest edge tree
B. abyssinica
(V erdcourt,
1958). Similarly, the small pink-flowered Nguru
shrub
Soineia calantha
presumably originated
from the widespread lowland, submontane and
montane forest tree .
maagascariensis.
The vey
variable
Mitriostma
with two West African spe-
cies and three southen and eastern African spe-
cies (Bridson, 1979; Bridson & Verdcourt, 1988;
Verdcourt, 1987) has a montane orest Eastern
Arc endemic,
M. usambarensis
ith robust pink-
purple flowers, which may have been derived
from the widespread and closely related white-
flowered
Oyanthus.
In addiion to pink lowers, longer peduncles or
pedicels is a character of Easten Arc forest
endemics originaing from more widespread spe-
cies. For example. the Uluguru and Uzungwa
endemic
Craterispemum longipedunculatum
has
longer peduncles than the more widespread
.
schweifurthii;
the montane Uzungwa endemic
Dypetes gerrardinioies
has longer pedicels than
the related East and West African lowland
D.
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