(BONDO UNIVERSITY COLLEGE)
FACULTY OF EDUCATION
SCHOOL OF ENVIRONMENT AND EARTH SCIENCES
DEPARTMENT OF GEOGRAPHY
NAME: OCHIENG’ GABRIEL
REGISTRATION NO: ED/5104/2008
TERM PAPER TOWARDS THE PARTIAL AWARD OF THE DEGREE OF BACHELOR OF EDUCATION (ARTS) WITH IT
5. Citing specific examples, discuss the physiological, morphological, behavioral and anatomical adaptative traits of biomes in: a) ASAL ecosystems and
b) Tundra ecosystems.
1. Critically examine the relevance of the theory of natural selection in biogeographical studies.
DATE: AUGUST, 2011.
ARID AND SEMI-ARID LANDS ECOSYSTEMS
The deserts of the world are areas in which there is a great deficit of water. They are areas with great moisture shortage. This is usually determined by the high temperatures that determine many of the characteristics of the soils, the vegetation, the animals and the landforms and human activities of such areas. Modern systems of defining aridity tend to be based on the concept of water balance, the relationship that exists between the input of water in form of precipitation, the losses arising from evaporation and transpiration (evapo-transpiration) and any changes in storage (soil moisture, groundwater, etc). By definition, in arid areas, there is an overall deficit in water balance over a year and the size of that deficit determines the degree of aridity. Extremely arid areas cover about four percent of the earth’s land surface, arid about fifteen percent and semi-arid about fourteen point six percent. Combined, these amount to almost one-third of the earth’s total land area. The deserts occur in five great provinces separated by either oceans or equatorial forests. The largest of these by far includes the Sahara and a series of other deserts extending eastwards through Arabia to Central Asia. The Southern African province consists of the coastal Namib Desert and the Karoo and Kalahari dry zones. The South American dry zone is confined to two strips, the Atacama along the west coast and the Patagonian Desert along the east coast. The North American desert province occupies much of Mexico and the south-western United States, including the Mojave and Sonoran Deserts. The fifth and final province is in Australia. Vegetation:
Shrublands, grasslands and woodlands are observed in the arid regions. The plants found in such areas include the cactus, date, oleander, etc. The Sahara desert plants grow mostly in regions along the Nile River and the highlands. The northern region of the Sahara that is along the Mediterranean Sea, has olive plants in large numbers. The highlands of the Sahara have plant growth in the form of doum palms, oleanders, date palms, etc. The nature of plant life in arid regions is highly dependent on the fact that they have to adapt to the prevailing aridity. There are two classes of vegetation: perennials, which may be succulent and are often dwarfed and woody; and annuals or ephemerals, which have a short life-cycle and may form a fairly dense stand immediately after rain. The ephemeral plants evade drought. Given a year of favourable precipitation, such plants will develop vigorously and produce large numbers of flowers and fruit. This replenishes the seed content of the desert soil. The seeds then lie dormant until the next wet year, when the desert next blooms again. The perennial vegetation adjusts to the aridity by means of various avoidance mechanisms. Most desert plants are classified as xerophytes, that is, plants that can withstand water shortages for long periods. They possess drought resistant adaptations: transpiration is reduced by means of dense hairs covering waxy leaf surfaces, by the closure of the stomata to reduce transpiration loss and by the rolling up or shedding of leaves at the beginning...