Large expanses of land in the tropics do not receive enough rainfall to support extensive tree cover. The Tropical and Subtropical Grasslands, Savannas, and Shrublands are characterized by rainfall levels between 90-150 centimetres per year.
However, there may be great variability in soil moisture throughout the year. Grasses dominate the species composition of these ecoregions, although scattered trees may be common. Large mammals that have evolved to take advantage of the ample forage typify the biodiversity associated with these habitats.
These large mammal faunas are richest in African savannas and grasslands. The most intact assemblages currently occur in East African Acacia savannas and Zambezian savannas comprised of mosaics of miombo, mopane, and other habitats. Large-scale migration of tropical savanna herbivores, such as wildebeest (Connochaetes taurinus) and zebra (Equus zebra), are continuing to decline through habitat alteration and hunting.
They now only occur to any significant degree only in East Africa and the central Zambezian region. Much of the extraordinary abundance of Guinean and Sahelian savannas has been eliminated, although the savannas in the Sudd region are one of the last places where large-scale migrations of Ugandan Kob still occur.
Both the Cerrado and the Llanos are noted for complexity of habitats and the unusually high levels of endemism and beta diversity in plants for tropical savannas. The tropical savannas of northern Australia and southern New Guinea exhibit distinct species assemblages and higher taxa.
Diverse large mammal assemblages in abundant aggregations can be a characteristic feature; most vertebrates display relatively widespread distributions; plant alpha diversity is typically low, but in some regions beta diversity and gamma diversity can be very high.
Large natural landscapes are necessary to allow large grazers and their associated predators to track seasonal rainfall or to migrate to new areas during periodic droughts; large-scale fire events also necessitate the conservation of larger natural landscapes; some large predators, such as wild dogs of Africa, require large natural areas to persist due to home range size and sensitivity to humans; sources of water are critical for many species.
Sensitivity to Disturbance
Restoration potential in these systems is high; but plowing, overgrazing by domestic livestock, and excessive burning can quickly degrade and alter natural communities; alteration of surface water patterns can have significant impacts on the persistence of many vertebrate species; many species are highly sensitive to low intensity hunting or other human activities.