Explain the differance between savanna and desert?
Savanna : Savanna is characterized by relatively low rainfall and pronounced dry seasons. This type of climate produces a biome that typically has wide sweeping grassland punctuated by randomly dispersed shrubs and solitary trees. Some describe savanna biomes as being inbetween tropical rain forests and deserts.
Rainfall in savannas average about 100 to 150 cm (40" - 60 "per year, and the dry spells last for long periods of time, producing drought conditions. Drought conditions produce mass migrations of animals every season.The dry landscape also accounts for the sparse distribution of trees and shrubs. As you might expect, grass fires are often a part of this biome. Savannas are typically found in Africa, South America, and Australia, and support large-hooved grazers such as giraffes, wildebeests and zebras. Big cats like the lion and cheetah represent the carnivore feeding level in Africa.
Desert : Deserts are characteristically very dry regions with rainfall under 25 cm (10 inches) that experience wide swings in daily temperature. In some deserts in Libya and Mexico, the temperature drops 30 degrees C (54 degrees F) at night, making for very extreme living conditions. The reason for large temperature fluctuations lies in the lack of water, ground cover and sparse vegetation, which usually absorb and hold heat. Without these heat reservoirs to trap heat, the ground loses its heat rapidly through radiational cooling.
Rainfall is not necessarily a sure thing either, as some deserts have gone without rain for over 2 years! And then when it does rain, it comes in a short period of time, and the water doesn't get a chance to soak into the ground, resulting in flash flooding. Flooding more often than not reshapes the desert landscape, making for an unstable substrate to grow on.
Plants take advantage of the rainy season, and sprout flowers as soon as the rains come. So, desert perrenials produce a striking bloom of flowers resulting in seeds, which must then survive the coming dry spells. Annual plant seeds also germinate while water is available, producing a flush of growth in the desert.
As you might expect, any organism that is able to survive these extreme conditions and call the desert its home must have an array of special adaptations and strategies. Indeed, plants are able to retain water by having thick, succulent stems and small leaves that reduce the evaporative surface. In fact, cactus leaves have become modified into spines, which also discourage grazing animals. The number of stomates are minimal to prevent water loss, but this required a special mechanism to take up CO2 at night, when the stomates could open. Since leaf area is reduced, photosynthesis occurs on the stem surfaces.
Animals also have adaptations that enable them to survive in the harsh environment of the desert. The predominant species found in desert conditions are represented by reptiles, arthropods, birds, and small mammals--especially the rodents. Strategies employed by desert animals include behavioral as well as anatomical and physiological adaptations. Bird migrations are keyed to the seasons, and many desert dwellers are nocturnal, restricting their activities to nightime to avoid the heat of day. Some birds, rodents and amphibians are able to go through a period of dormancy, or hibernation called estivation during the dry spells. Desert rodents burrow deep into the desert floor to escape the heat during the day, and come out at night to feed. However, owls and snakes are also nocturnal hunters!