The following HTML text is provided to enhance online
readability. Many aspects of typography translate only awkwardly to HTML.
Please use the page image
as the authoritative form to ensure accuracy.
and monitor progress toward achieving objectives? This question is examined by drawing on experience in several southern African countries against a background of the diversity and dynamics of African ecosystems.
Africa broke away from South America and the rest of the ancient supercontinent of Gondwanaland some 140 million years ago. Dinosaurs and gymnosperms occupied the landscape but were soon replaced by mammals and the flowering plants that we know today. Equatorial rain forests dominated the vegetation for a long period and were only replaced by the savanna systems characteristic of most of Africa today at the onset of the Pleistocene ice age, some 2 million years ago. Throughout the Pleistocene epoch the expansion and shrinking of the polar ice caps were reflected by major changes in the global climate. Cooler, drier periods of approximately 100,000 years alternated with shorter, warmer, and moister spells, and variants of these. This exerted major environmental pressures on the continent’s flora and fauna. What we see of African ecosystems today is merely a narrow slice of the diversity that has existed on the continent throughout time. Through much of these massive oscillations of Pleistocene climate and vegetation, humans have exerted a profound influence on the shaping of African environments both as hunter and fire maker. A consequence of these varied influences is the tremendously dynamic character of African ecosystems, in which both speciation and extinction are ongoing processes.
PATTERNS OF SPECIES RICHNESS AND ENDEMISM
Students of plant and animal distributions have divided the world into eight major regions, or biogeographic realms, one of which is Africa south of the Sahara. Known as the Afrotropical realm (Udvardy, 1984), it includes not only sub-Saharan Africa but also the island continent of Madagascar, the islands of the western Indian Ocean, and the southern tip of Arabia. It possesses the richest mammal fauna of any realm and a rich and distinctive fish fauna but relatively impoverished bird, reptile, and amphibian faunas. The flora of tropical Africa is not nearly as rich as that of South America or Southeast Asia, but that of southern Africa is extraordinarily rich.
Of the 20 biogeographic units defined for the African continent, 17 fall within the Afrotropical realm and 7 of these are recognized as centers of endemism, the cradles of floristic evolution and speciation (White, 1983). The species richness and percentage of species restricted to each center of endemism are summarized in Table 29–1. Plants, birds, and fishes provide excellent examples of the differing patterns of biological diversity in Africa and can be used to illustrate the vulnerability of localized centers of species richness to human-induced impacts. The examples chosen also demonstrate that much of Africa’s biotic wealth lies outside the tropical savannas, which have enjoyed so much attention from wildlife conservation organizations.