Ecosystems and Ecology
Ecosystems and Ecology
Author: Prof Koos Bothma
Licensed under a Creative Commons Attribution license.
BIOMES, ECOSYSTEMS AND BIOREGIONS
The concepts of biomes, ecosystems and bioregions are vital in the management and conservation of
renewable natural resources. The major difference between these concepts lies in the principle of scale.
Biomes are major biotic units with similar and characteristic biota and structure. While there are several
distinctive global biomes their boundaries may merge and become indistinct. Biomes are high-level
hierarchical and consequently simplified biotic units, within specific restraints imposed by their physical
environment. The terrestrial biomes are characterized by their dominant plants which support specific
types of animal. The principal global terrestrial biomes are: temperate deciduous forests, temperate
coniferous forests, tropical forests, grasslands, tundras and deserts. Other biomes occur regionally. For
example, in South Africa, Lesotho and Swaziland the biomes are fynbos, the succulent Karoo, the NamaKaroo, grasslands, savannas, the Albany Thicket, deserts, forests and the Indian Ocean Coastal Belt.
Within these biomes there are numerous bioregions and ecosystems. Full details of the biomes and
bioregions appear in Mucina and Rutherford (2006) in the reference below.
Namib Desert, Gobabeb, Namib Naukluft National Park, Namibia - June 1978
Ecosystems occupy the next hierarchical level of scale and reflect a specific set of interrelationships
between various organisms and their physical environment (see Section 3). Their biotic component
consists of plants, animals and micro-organisms that are the producers, consumers and decomposers,
which harness the solar energy that reaches the Earth. It is estimated that most of the 15.3 x 108 gram
calories per square metre of solar energy that reaches the Earth’s surface is dissipated by dust or is
consumed by water evaporation with only a small fraction becoming available for plant photosynthesis. At
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Ecosystems and Ecology
each level of transfer in an ecosystem food chain 80 to 90 per cent of the energy being transferred is lost
as heat. This limits most food chains to four or five hierarchical levels. Humans have only recently
become the apex of the global food chain but are already placing a severe strain on ecosystems by
destroying the energy base levels on which their survival depends. The oceans are mostly unproductive
and humans largely utilize the apex predatory fishes of the oceanic food chains as a source of nutrition.
Bioregions are composite spatial terrestrial units within an ecosystem that possess similar biotic and
physical features and processes on a regional scale. In the Savanna Biome of South Africa, for example,
there are six bioregions: the mopaneveld, the sub-escarpment savanna, the Kalahari duneveld, the
Lowveld, the central bushveld, and the eastern Kalahari bushveld. Elsewhere in southern Africa the
miombo and Brachystegia woodlands are additional major bioregions. A bioregion is therefore an
intermediate biotic level between a biome and a vegetation unit. In a bioregion specific biota are central in
importance but the concept of a bioregion focuses on plant diversity rather than on animal diversity.
Lowveld savanna, Satara, Kruger National Park, South Africa - May 1971
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