The montane butterflies of the eastern Afrotropics - Biogeography and Ecology of the Rain Forests of Eastern Africa - page 146

restricted to single mountains renders this fauna
of disproporional interest.
It is not clear why there are many fewer mon-
tane forest species than lowland forest species.
One reason could be that the area of the montane
forest is much smaller. This may be so, but on the
other hand the area is strongly split up, offering
more opportunities for speciaion events. Another
reason for the relatively low number could be the
young age of the montane forest. This is,
however, very uncertain. Part of the Eastern Arc
mountains is supposed to have been uplifted dur-
ing Jurassic times (Moreau, 1966). If true, these
early mountains could have carried forests at
higher altitudes at a ime when the butterflies as a
group did not even eist. The extent, however,
could have been very limited, and most of the
present area of montane forest is certainly not
older than a few million years. Sill another reason
could be that the montane forest fauna suffered
much from climaic vicissitudes and could not be
supplied from the rich lowland forest to the west
by sheer distance (there were, and sill are,
patches of lowland forest along the east coast, but
they are rather poor in species). This explanation
is unlikely since an important refugial area oflow-
land forest during extreme contracion of the for-
est is supposed to have been at the eastern rim of
the Congo basin against (or even in) the moun-
tains fringing the great lakes from Lake
Tanganyika to Lake Mobuto (Hamilton, 1981,
1982; Crowe & Crowe, 1982). This mountainous
area (to be called the Western Border Range,
below) is not even the area richest in montane
forest butterflies. Maybe an explanaion of the
relatively low number of montane forest butter-
flies is quite simple and should be sought in an
ecologically less diversified environment with
stronger constraints (e.g. lower temperature).

Conlusion

The montane grasslands of EAT are populated by
butterfly species of widely different origins. A
proporion of the species occur at lower elevaions
and/or in other habitats as well. The species that
are more or less restricted to this kind of habitat
have mainly originated on the spot from species
with other habitat preferences. A much smaller
proporion of the fauna (20-28%) originates from
an influx from outside, particularly from the north
(Palaearctic and Oriental regions).

Forests

General

The butterfly fauna of Africa numbers well over
3200 species (Carcasson, 1981). Of these about
56% are restricted to forests. The forest species
are not evenly distributed over the forest area: by
far the greatest diversiy is found in the large
central forest block. In view of its size this is not
remarkable, but it is not only area that determines
the number of species: perhaps more important
are the vicissitudes in the extent of the forest over
geological ime and the diversity in the tpes of
forest. By far the majority of forest species are
restricted to low and/or medium levels. Although
a number of these species may ascend to higher
levels, the butterfly fauna usually changes with
increasing altitude and species restricted to higher
levels appear. In EAT there are forests at all
alitudinal levels, although most forests at low and
medium levels have been destroyed in historical
times by human intervention, strengthening the
isolation of the montane forests. Forests at low
and medium elevaion are ound in east Zaire,
Uganda, west Tanzania, east Tanzania (Usam-
bara, Nguu, Nguru, Uluguru, Uzungwa; patches
along the Indian Ocean coast), Kenya (patches
along the coast and at medium levels in west
Kenya) and Malawi. We are concerned here with
the montane forest butterfly fauna only. In EAT,
where by far most of the montane forest species of
Africa occur, they number 177. Although this
number is low relaive to the number of lowland
species, the disjuncions and the many endemics

Scenarios and predicted pattens

Unless the butterflies as a group originated in the
highland forests of EAT (which is most unlikely,
if only because of the fact that the butterflies as a
group already eisted long before the greater part
of EAT was uplifted), the montane forest butter-
flies of eastern Africa must have come from