Geology Reference
In-Depth Information
and indeed perhaps easten Africa, and that they
are virtually unknown biologically, there is every
reason to believe that further work will reveal
more species in common with the more northerly
mountains of the Easten Arc as well as others
endemic to the Uzungwas, as would be predicted
by current island biogeographic theory (MacAr-
thur & Wilson, 1967).
It has not been possible to obtain enirely com-
parable figures for comparison from other parts of
Africa: apparently no complete species lists with
sufficiently detailed habitat data have been
published. Schi0tz (1967) gave a parial list offrog
species (excluding Arthrolepidae) from the for-
ests of West Africa. If the West African forest
block is considered in its enirety, there are five
genera of West African forest Hyperoliidae not
found in the Eastern Arc forests: Acanthixalus,
Callixalus, Ch ysobatrach us, Cyptothylax and Op is-
thothylax (Drewes, 1984). Seven ranid genera
present in the west are not found in the forests of
the Easten Arc according to Schi0tz (196 7), who
noted that for amphibians, richness of the Usam-
bara and Uluguru forests was comparable to that
of the forests of Ivory Coast and Ghana (Schi0tz,
The coastal forests have only very few forest-
dependent species (Table 9.1). Some of these are
limited generally to this type of vegetaion.
Others, in contrast, are limited to vey speciic
sites. Two anurans are known only from Kenya's
coastal forests. A skink is endemic to the Rondo
Plateau, and a gecko to Jozani Forest on Zanzibar.
While no precise data are available with which
to compare endemism in forest repiles with other
African localiies, D. Stubbs (in it. ) has compiled
a preliminary list of endemic amphibians for
various African countries. As he notes, the vast
majority oflocally endemic amphibian species are
concentrated in the moist tropical forest belt of
Central Africa and the mountain forest areas. He
also emphasises that among the small West Afri-
can states, endemics are extremely localised, and
many are known only from type localiies.
Although Stubbs's list is not restricted to forest
species, it does provide at least some relaive idea
of the diferences between various localiies in
Africa. The coninental African countries with the
highest levels of endemism are: Cameroun,
62/90; Zaire, 51/74; Tanzania, 40/51; Ethiopia,
30/31; Angola, 23/24. On Madagascar, all 144
forms are endemic (D. Stubbs, in it.).
The radiaion ofgenera and species inthe West
African forests is reflected in a number ofspecies
with unusual adaptations related to their ecology
and reproducion. For example, the reefrog
Acanthixa/us sp inosus is apparently mute and
breeds in small amounts ofwater trapped in trees.
Several ranid genera not found in the easten for-
ests, such as Conraua, Petrpeetes, Asy/ostenus,
Scotoblep s and Tichobatrachus have been regarded
as specialised stream dwellers (but see Wasser-
burg & Heyer (1983), who argue that tadpoles
thought to be adapted to living in swift-flowing
streams may actually be specialised for living in or
near flowing water but not in a mainstream
Laurent (1973), in a comparaive survey of the
amphibians and repiles of Africa and South
America, describes various adaptaions and con-
vergence. I am, however, unable to account for his
statement 'In Africa, microhylids are absent from
the orest' (p. 261), as Cal/u/ina and Probrviceps
are enirely resricted to the easten forest. He
The rends seen or diversity also apply when
endemism is considered (Table 9.4). Levels of
endemism are comparable for the Usambaras and
the Ulugurus. In the Usambaras there is a slightly
higher level of endemism among repiles (37.5%)
when compared with the Ulugurus (33.3%).
The situaion is reversed for the amphibians:
the Uluguru forests have 26% of the species
endemic, while those of the Usambaras have
21.7%. The herpetofauna of the Uzungwas has
only recently been recognised to contain many
species formerly believed to be Usambara/Ulu-
guru endemics (see the secion above on diversity)
and appears to have levels of endemism lower
than those of either the Usambaras or Ulugurus.
Further south, Mount Rungwe has no endemics,
and the forests of Malawi have only a single
endemic species ofArthrolptis. To the north, the
Taita Hills forests have a single endemic
amphibian burrowing form.
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