Overview of Tropical Grasslands Ecosystems
Tropical grasslands ecosystems, also known as savannas, are located to the north and south of the equator, primarily between 5 and 30 degrees latitude, lying in between the tropical rainforests at the equator, and the deserts. Tropical savannas occur in Africa, South America, parts of Mexico, and northern Australia, and each is characterized by its own distinctive flora and fauna.
The climate of tropical grasslands ecosystems is warm year-round, and has two distinct seasons, wet and dry. The length of the rainy and dry seasons varies with distance from the equator; the dry season lasts for 3-4 months in regions nearer the equator, and 8-9 months in areas closer to the desert. Average annual rainfall ranges from 20 to 60 inches (500 to 1500 mm).
Fire plays an important role in tropical grasslands ecosystems. Fires started by lightning commonly occur during the dry season. Such fires are a natural part of the ecosystem, and do not pose a significant risk to the survival of the species that live there. Larger animals are generally able to outrun the fire, and underground burrows provide safe havens for small burrowing animals when a grass fire sweeps across the plain.
Vegetation of Tropical Grasslands Ecosystems
While the vegetation of tropical grasslands is dominated by many different species of perennial grasses and sedges, some trees, woody plants and shrubs also grow there. The trees display many drought-resistant and fire-resistant adaptations, such as being shorter than the trees in a forest environment, and having small waxy leaves and thick, fire-resistant bark. Most trees also have deep roots and are capable of re-growing from the roots if the upper part of the tree is destroyed. Trees in the African savanna often have spines to protect them from browsing herbivores. Notable tree species found in tropical grasslands ecosystems are the baobab and acacia.
Animals of Tropical Grasslands Ecosystems
All of the animal species that live in tropical grasslands are adapted to conditions of intense sunlight, high temperatures and limited water. Some physical adaptations include light colored or partially white coats that reflect light, panting instead of sweating, and reduced urine output and increased absorption of water by the intestines to minimize water loss. Smaller mammals tend to be nocturnal, staying underground during the heat of the day and emerging after dark to look for food.
The animals that live in tropical grasslands ecosystems vary according to location, although some species of invertebrates, such as termites, are found in tropical grasslands throughout the world. Described below are some of the significant animal species found in the three main tropical grasslands ecosystems.
Africa- African tropical grasslands are noted for the large number of species of browsing and grazing mammals. Hoofed mammals include water buffalo, antelope, impala, eland, oryx and wildebeest. Other species of herbivores include elephant, rhino, zebra, giraffe and hippopotamus. These herbivores provide food for large carnivores such as lions, leopards, cheetahs and panthers. In addition to these large mammals, the African savanna is populated by numerous other creatures including bats, insectivores such as pangolins and aardvarks, small carnivores such as jackals and weasels, and a wide variety of small mammals and birds.
South America- The tropical grasslands in South America include the llanos, areas in river basins that become flooded periodically, and cerrado, the high table lands of Brazil. The llanos have a particularly high level of biodiversity. Some animals living in the llanos include capybaras, caimans and armadillos. The Brazilian cerrado occupies over 2 million square km (770,000 sq mi). There are hundreds of species of trees and shrubs, as well as armadillos, monkeys, opossums, and many rodents and birds, including the flightless rhea. The largest carnivore in the cerrado is the lobo guara, or maned wolf.
Australia- Only one carnivore, the dingo, is native to Australia. Large mammals in the Australian tropical grasslands ecosystem consist of marsupials including wallabies, wallaroos and bandicoots. The Australian tropical savanna is also home to the emu, a large flightless bird, as well as many small mammals, reptiles and birds including parrots, cockatoos and lorakeets.
Woodward, Susan L. Biomes of Earth. Westport: Greenwood Press, 2003.
"The Grassland Biome." University of California Museum of Paleontology, www.ucmp.berkeley.edu