ABSTRACT
The high mountains of Africa rise above the continental surface as terrestrial islands, on which their degree of isolation from similar neighbouring habitats increases with altitude. At these higher levels we observe a high degree of endemicity in both the flora and fauna. These Afromontane environments owe their origins to ancient tectonic, and more recent volcanic activity, so that many of these speciation processes seem to be reflected in the mountain’s age.
Climatic changes in the past have been responsible for the alternate contraction and expansion of the lowland and highland forest habitats, which must have resulted in one of the major isolating mechanisms driving speciation.
The Afroalpine flora of the East African mountains exhibits a remarkably high level of species endemism, although the montane forests contain far fewer endemics, with the majority of tree species being closely related to lowland forest forms. The effective long term isolation of the alpine regions suggests that long distance dispersal by wind and to a lesser degree by birds must account for the widespread distribution of many genera and species.
The distribution of montane butterflies and birds indicates a former highland forest connection between East and West African montane habitats. While the montane mammal species suggest that they have achieved their present distribution via a northern and southern route from the Ruwenzori region to the Kenyan and Tanzanian highlands respectively. The differing ages of the main montane isolates is strongly reflected in their patterns of animal speciation.
Recent palaeoclimatic research implies that during an intensely dry period little more than 20,000 years ago a profound extinction spasm may account for the species impoverishment of the Ethiopian highlands and perhaps even the lowland humid forests.
