Geology Reference
In-Depth Information
Table 8.5. Distribution of montane orest buttely sp ecies over combined mountain areas, and occurence in
Cameroun or ep lanation, see Ta ble 8. 1)
Shared with
N
%(endN)
%
N(end)
%(end7)
Cameroun
1 Ethiopia
10
5.68
4
40.00
2.27
3
2 C Kenya
36
20.45
4
11.11
2.27
8
3 W Kenya
42
23.86
4
9.52
2.27
12
4 N Tanzania
35
19.89
4
11.43
2.27
6
5 E Tanzania
89
50.57
56
62.92
31.82
6
6 Malawi
37
21.02
8
21.62
4.55
6
7 W Tanzania
35
19.89
2
5.71
1.14
9
8 W Range
67
38.07
30
44.78
17.05
15
merly Lake Albert), stand out because of their
high numbers of endemics.
inated in the Easten Arc mountains and
epanded their ranges there ever reached other
areas to the north (Kilimanjaro, Mount Meru,
Disrict of Great Craters, together listed as north
Tanzania in Table 8.5) and to the south (Nyika
Plateau). There are exclusive connecions
between these areas and the Easten Arc moun-
tains. Three species (Papilio honimani, Nptis
auivillii and Biyclus anckelmant) are found only
in north Tanzania and the Eastern Arc moun-
tains. Similarly, four species Metisella deipiens,
M. nyika, My lothris rawshayi and Uranothauma
cuneatum), and two subspecies (Papilio esmondi
usambarensis and Charaxes ansorgi levickt) are
found only in Nyika Plateau and the Easten Arc
mountains. We do not suggest that all these taxa
originated in the Easten Arc mountains: they
merely indicate that at their northen and
southen ends the Easten Arc mountains had
contacts with other areas. Most of the taxa con-
cened have a rather wide disribuion in the
Easten Arc mountains and are apparently rather
good dispersants.
(a) In the Easten Arc mountains 36 of the 56
endemic species occur in one ofthe areas, leaving
only 20 species that are distributed over two or
more areas. These mountains form a chain in
such a way that absence of a taxon in an interven-
ing area is likely to be the result of undercollecing
or exincion and does not indicate a historical gap
between the areas. Thus occurrence of a species
in two areas separated by two other areas indicates
coherence of all four areas rather than a special
connection between two. Seen in this light and
focusing on the 56 species that are resricted to
the Easten Arc mountains, only two species
(Papilio fu eleboni and Uranothauma williamst) can
be said to indicate the coherence ofall eight areas,
although the former is not known from one area
and the latter from two. Two more species
.mpittia pava and Ep amera dubiosa) connect
seven areas, from the Usambara Mountains to
Uzungwa. In comparison with the number of
endemics in the Usambara Mountains (12 spe-
cies, 15 taxa if subspecies are included), Nguru
(7, 8), Uluguru (8, 10) and Uzungwa (8, 8) these
numbers are too low to suppose that the Easten
Arc mountains ever formed a single area of evolu-
ion (i.e. a single isolated area). It rather seems
that the four areas just menioned were each, so to
say, nuclei of speciaion rom where some of the
new species spread to nearby areas.
It is unlikely that none of the species that orig-
(b) The Westen Border Range encompasses the
following areas of Table 8.4: 24 (Marungu
Plateau), 25 (north end of Lake Tanganyika), 26
(Kivu area), and 27 (Rwenzori to Lake Mobuto).
None of the taxa endemic to the Westen Border
Range occurs on the Marungu Plateau, so we
leave this area out of further consideraion and
resrict the Westen Border Range to the moun-
tains between the northen
end of Lake
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