Geology Reference
In-Depth Information
Table 7.4.
Sp ecies ichnss and nemism of 'true
forest sp ecies ' of
I
inphiid sp iders within four orest
areas in East Africa
tains in the period 1980-4 revealed the following
pattens (Tables 7.5 and 7.7).
In the Mwanihana Forest Reserve, where col-
lecing was carried out at 100 m intervals along an
alitudinal gradient from 300 to 1850 m, it was not
possible to show any dividing line between a low-
land and highland fauna. Thus, even though there
is a clear difference between the species composi-
ion of the linyphiid fauna of the lowest and
highest parts of the forest, it is not possible to
show any critical alitude separaing lowland or-
est from highland forest.
n
intermediate rain forest zone, where species
from higher alitudes have their lower limits and
where species rom lower alitudes have their
upper limits have been suggested by ornithol-
ogists (Moreau, 1935) for the Usambara Moun-
tains, between 750 and 1350 m. A similar
intermediate forest zone has been suggested for
the easten part of the Uluguru Mountains
between 800 and 1500 m, by botanists (Pocs,
1976) and for the Uzungwa Mountains between
750 and 1250 m (Rodgers & Homewood, 1982).
From Tables 7.5-7.7 it can be seen that such a
zone of mxture does also eist for the linyphiid
fauna, but the extension of the zone differs
between species and also between the two moun-
tains invesigated (Uzungwa and Uluguru). Fur-
thermore, it is not possible to find any species
resricted to an intermediate rain forest zone; the
linyphiid fauna changes gradually.
n interesting case of alitudional distribuion
is shown by species of the genus
Ophynia
on the
Uluguru Mountains (Table 7.5). A remarkably
high number of
Op hynia
species have been
recorded from this mountain and the species do
not show an even distribuion. Two species
(0.
summicola
and
0.
infeaa)
are resricted to the
ridge top (elfin forest) and have not been found
below 2100 m. Another species
(0.
ga/eata)
is
ound above 1800 m on the westen side of the
mountain and down to 1100 m on the easten side
(near the present man-made forest edge on the
easten side). The fourth species
(0.
rvelatix)
has been recorded only from the westen side
where it occurs between 1400 and 1800 m (a
man-made forest edge has been created on the
westen side, below Lupanga Peak, at 1400 m).
Number of Number of Percentage
species
endemics
endemism
Site
Uluguru Mts 14
Uzungwa Mts 31
Mt Kenya
12
25
5
4
86
81
33
25
15
Mt Elgon
16
No te:
The high number of forest species recorded from
the Uzungwa Mts represent data from several forest
areas.
Source:
Scharff (1992).
each mountain, but there are big differences in
the degree of endemism - the moist forest areas
of individual mountains ofthe Easten Arc have a
much higher degree of endemism (Table 7.4)
(Schar, 1992).
Alitudinal disribuion of species
Very little is known about the alitudinal disribu-
ion ofEast African linyphiid species. Studies car-
ried out on Mount Kenya in Kenya have shown
that the linyphiid fauna of the montane forest area
on this mountain is very different from that of the
higher Afroalpine area (Holm, 1962; Bosmans,
1977, 1979), but very little inormaion is available
from the East African lowland areas. Thus,
nothing is known about the difference, if any,
beween the fauna of lowland and highland for-
ests. A further complicaion is the fact that there
are only a few areas left in East Africa where
studies of forest communiies can be carried out
in a coninuum from lowland to highland forest
habitats, since most areas have lost their forest
cover below 1500-2000 m during the last 100
years. One of the very few areas where such a
study can sill be carried out is in the Easten Arc
mountains, where the easten side of the
Uzungwa Mountains and Mount Kanga carries a
coninuous orest cover from about 300 m to
2000-2500 m. Collecion along alitudinal
gradients in the Uluguru and Uzungwa moun-
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