Geology Reference
In-Depth Information
Benardi, 1979). Sill higher, the Ericaceae are
replaced by an alpine vegetaion and eventually by
bare rock (etage aro-alpin: Benardi, 1979). In
EAT these belts are found only on the young high
mountains, mainly of volcanic origin, like Mount
Elgon, the Aberdares, Mount Kenya, Kilimanjaro
and Mount Meru. Since the mountains of the
Easten Arc are not high enough to support these
belts, the treament of the other mountains here
seems out of place; they are included only for the
sake of completeness. Moreover, it must be kept
in mind that at the height of the last glaciaion c.
22 000-14 000
BP,
when the vegetaional belts
were displaced downwards by about 1000 m
(Hamilton, 1982, 1989), this type of vegetaion
must have been much more widespread, and part
of the Easten Arc mountains may have acted as
stepping stones for dispersal of organisms adap-
ted to this environment. For the butterflies,
however, this is irrelevant since there are no spe-
cies resricted to this type of habitat in Africa. The
butterflies that do occur here are from lower
alitudes. Coe (1967) reported that they can be
numerous in the alpine zone of Mount Kenya
where they may even be found flying above the
glaciers. According to Coe these butterflies are
brought there by air currents during the day. At
night they die from the intense cold and fall into
the ice. Next moing the body and wings absorb
the sun's heat which melts the ice below the body,
and the insect slowly sinks into a small pit. The
diversity of these butterflies is apparently very low.
Coe menioned four species only:
of the Oriental Region, throughout North
America, and as a straggler in Westen
Ausralia.
Hapendyreus aequatorialis (Sharpe, 1891) - a
lycaenid of the montane grasslands of
Kenya and northen Tanzania (see also
below);
Zizula hylX
(Fabricius, 1775) - a small but very
widespread lycaenid occurring throughout
the Afroropical and Oriental regions.
The absence of rue alpine butterflies in Africa
is surprising in view of the relaively high diversiy
of alpine butterflies in the Holarcic. In the higher
alitudes of the Andes, Descimon (1986) also
observed a poor butterfly fauna compared with
the Holarcic in spite of the large extent of
apparently suitable habitats. He also remarked on
the poor butterfly diversity in Africa, but the spe-
cies he menioned mainly belong to the montane
grassland. He explained the poverty in butterflies
of the African oreal regions by 'the youth, the
small size and the isolaion of these montane
islands'. Indeed, the alpine biome in Africa may
be not older than 1-2 Myr
BP,
when the great
volcanoes arose, and certainly its isolaion rom
the much older and richer Palaearcic alpine
biome was and is so severe that one cannot
imagine even a very long distance dispersal. On
the other hand, its age was great enough for a
highly specialised and endemic flora to develop
(see, for example, Hedberg, 1986). The key factor
for the species poverty in butterflies may be eco-
logical rather than historical, such as absence of
suitable food plants. So far, however, this is
speculaion.
Golias eleao (Linnaeus, 1763) - a widespread
pierid occurring from southwesten Arabia
and northen Ethiopia to South Africa,
especially in montane grasslands; in South
Africa it is one of the commonest and
most widespread species (Dickson, 1978)
(see also below);
Va nessa cardui (Linnaeus, 1758) - a strongly
migratory nymphalid, probably the most
widespread butterfly of the world
occurring throughout Africa, the warmer
parts of Europe and temperate Asia (in
spring migraing northward as far as
Iceland and northen Scandinavia), most
Montane rasslands
General
Montane non-forest habitats have attracted much
less attenion than the Aroalpine and montane
forest habitats. One reason may be that the habitat
is poor in characterisic species. It is not a uniorm
habitat, varying from woodland to open grassland.
We shall confine ourselves to the grassland since
this habitat seems to have more characterisic spe-
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