Africa is well endowed with both variety and abundance of living things, together referred to as biological diversity, or biodiversity. That biodiversity, with some exceptions, is currently in a better condition than in many parts of the world. Biodiversity can be considered at three major levels:
- The genetic variation within populations;
- The number, relative abundance and uniqueness of species; and
- The variety, extent and condition of ecosystems.
Broad geographical patterns
Ecosystems are broadly arranged in a latitudinal pattern, with increasing species richness towards the equator. However, plant species richness is also high in the winter-rainfall Mediterranean climate regions of Northern Africa and the southern Cape. In between are the subtropical deserts, which are generally a zone of lower diversity: for example, a vast part of the Sahara, the Ténéré, is home to only 20 plant species in an area of about 200,000 km2. Overlaid on these latitudinal patterns are pockets of rich biodiversity with small distribution ranges, particularly in tropical montane areas. From Ethiopia to the Cape, mountains contain several centres of endemism for birds, mammals, and plants. One of the most globally important centres of endemism is the coastal mountain range in the eastern part of Madagascar.
The increasing richness of plants and vertebrates toward the equator is related primarily to climatic factors, such as water availability, however the diversity of land variations, such as topographic, is also important. There are exceptions to this: some areas with harsh climates including, the Namib Desert and the Karoo in the west of South Africa have an estimated 4,500 plant species, a third to one-half of which are endemic.
Spatial patterns of diversity vary for different species, and the diversity and abundance of different species influence each other. For example, the Cape is a centre of plant diversity of global importance, but not a centre of diversity for mammals, birds, snakes and amphibians (Figure 1). The Central Zambezian Miombo woodlands located in Zambia, the Democratic Republic of the Congo (DRC) and Tanzania is a centre of bird diversity, but not of plant diversity.