members of the Proteaceae. All are adapted to a period of slow growth and the pre-
vention of water loss by closing stomata during the summer drought. The leaves are
hard and leathery, characteristic of sclerophyllous vegetation. In isolated areas, such
as southwest Australia or South Africa, plants show a high degree of speciation and
many of the species are endemic. There are several small mammals and passerine
birds adapted to the regime of summer drought, but their diversity is usually low.
For example, in California chaparral there is the wrentit (Chamaea fasciata) and
kangaroo rat (Dipodomys venustus). In the Mediterranean there is the Sardinian
warbler (Sylvia melanocephala), in South Africa the Cape sugarbird (Promerops cafer)
on proteas, and in Australia the western spinebill (Acanthorhynchus superciliosus)
feeding on banksias. The southwestern USA and Mexico are the centers of radia-
tion for oak (Quercus) and juniper (Juniperus) woodlands. There is an associated
fauna of birds and mammals that form a hotspot of biodiversity in North America
(Dobson et al. 1997).It is no accident that all the large herds of ungulates occur in the grassland biomes- caribou in the Canadian tundra, saiga on the Asian steppes, bison on the American
prairies, and various antelopes on the African savannas. They have in common the
ability to migrate in response to the seasonal climate and changing vegetation and
so place themselves in the areas of highest food production at the time. They avoid
thereby many of their predators who cannot migrate to the same extent. These two
abilities – to find temporary food patches and to avoid predators – allow a higher
density of animals than if the population did not migrate in a similar area; the large
herds are not just a consequence of the extensive area of these biomes.
Tropical savanna comprises grassland with scattered trees. Often the trees are sparse,
as on the open plains of East Africa, or quite dense with up to 30% canopy cover,
as in some of the Acaciasavannas of Africa and Australia. Although temperature is
fairly constant, rainfall is highly seasonal and falls in the range of 500–1000 mm.
Grasses are mostly perennial, 20–200 mm in height, and are usually burned each dry
season. Most savannas in Africa are maintained by fire rather than by soil moisture;
examples of the latter (edaphic grassland) are seen in the flood plains of the larger
rivers such as the Zambesi and Nile, or shallow lake beds of Africa, and the llanos
of the Orinoco in Venezuela.
The African savannas support a wide range of large mammal species, some com-
munities having as many as 25 ungulate and seven large carnivore species as well as
many rodent and lagomorph herbivores, mongooses, civets, and other small carni-
vores. The Australian savannas support an array of macropod herbivores (kangaroos)
but no large carnivores, although the three that used to occur have become extinct
on the mainland in the last 30,000 years. Small carnivorous marsupials are repre-
sented by dasyurids. In the birds, finches, parrots, and emus (Dromaeus novaehol-
landiae) are common. South American wet savannas, in Venezuela and the Pantanal
of Brazil for example, have a range of large rodents such as capybaras (Hydrochoeris
hydrochoeris) and coypus (Myocastor coypus) that partly take the place of ungulates
in Africa, but the drier pampas has very few large herbivores. There may be his-
torical reasons for their absence: in the Tertiary there were many endemic herbivores
belonging to the Notoungulate group which have since died out. Of the birds,
pipits, buntings, and tinamous are characteristic.BIOMES 15
2.5 Grassland biomes
2.5.1Tropical
savanna