Herpetofauna of the eastern African forests - Biogeography and Ecology of the Rain Forests of Eastern Africa - page 194

Bondwa in the Ulugurus at alitudes up to 1500
m. In natural clearings in coastal forest, other
non-forest amphibians also occur. The role of
these species in colonisaion and possible com-
peiion with forest forms remains unassessed.
Schiotz (1967, 1975) has called attenion to
what he termed a 'farm-bush' anuran fauna. He
notes that in many parts of Africa, the forest cover
has been removed or partially removed, and
natural vegetaion has been replaced with a
mosaic of culivation and isolated trees and/or
patches of forest. Sanderson (1936), in a discus-
sion of habitat preference of amphibians in
Nigeria and Cameroun, also noted that non-for-
est species may be found in clearings around villa-
ges surrounded by forest. Schiotz (1967)
suggested that at least for the treefrogs, a possible
explanaion may be that post-breeding dispersal
in the dry season would account for the occupa-
ion of new areas. He notes that this process
might take some years, and that Sanderson's
observaions were made 20 years after the iniial
clearing of a forest for a village. Schiotz's own
observaions were made much more recently after
clearing had taken place. He did not give precise
figures and noted that the non-forest species
found were sill relaively ew.
Likewise, when forest cover is reduced by large
mammals (see Kortlandt, 1984 for a review), by
natural die-of or by old rees which fall, open up
areas within the forest and change the character
of the vegetation, how do various forest-
dependent species persist? At least some species
are able to survive in the forest edge in recently
cleared areas, and some even appear to remain as
long as adequate cover of some dense vegetaion
persists, such as Bufo brauni (personal observa-
ions), Naja melanoleuca and Bitis gabonica (Ionides
& Piman, 1965). But Stewart & Pough (1983)
have shown that for a tropical forest frog the num-
ber of nest and rereat sites may be important
actors in the regulaion of populaions, and it is
unlikely that such species would be able to retain
their populaion levels once forest had been
cleared or the character of the vegetaion drasi-
cally altered.

The efect of man on the easten orests
and associated herpetofauna

When considering the past and present distribu-
ion of animal species in easten Africa, it is
necessary to understand geological, climaic and
evoluionary changes which have occurred on a
vast scale. The effect of man on the present dis-
ribuion of plants and animals is often overlooked
except in the most obvious sense hat he has been
responsible for much recent forest reducion that
has often completely destroyed forest communi-
ies. In easten Africa there are no exact data
available on forest amphibian and repile species
which have become exinct in historical imes;
menion has already been made of the frog Ath-
rolepties dutoiti on Mount Elgon, populaions of
which appear to have been greatly reduced, prob-
ably owing to logging operaions. The species has
not been collected since its descripion in 1935,
despite several attempts to obtain more specimens
of it. In southern Africa, Poynton (1986) has dis-
cussed man-made ecological changes · which
appear to have virtually eliminated a non-forest
frog.
Evidence eists, however, that man may have
been present in at least some of the forests of
eastern Africa thousands of years ago (Hamilton,
Taylor & Vogel, 1986; Hamilton & Bensted-
Smith, 1989) and that his aciviies such as clear-
ing and burning the forest may have had long-
term effects on the distribuion of vegetaion. I
have suggested above that clearings in forest may
be colonised by non-forest species, possibly by
means of post-breeding dispersal of juveniles
from outside the forest.
Another direct effect that man may have had in
the past and has at present is the creaion of con-
diions which avour hybridisaion of populaions
that under natural condiions would remain
ecologically isolated. Chapin (1948), for example,
documented hybridisation in populaions of the
Paradise flycatchers Te rpsiphone rufiventer and .
viridis (Aves: Passeriformes: Muscicapidae)
resuling rom forest clearing in easten Africa.
Hybridisation in anurans after environmental dis-
turbance is well documented in North America
(Blair, 1941;Jones, 1973; Feder, 1979; Gerhardt,