Hot Desert Ecosystem (AQA GCSE Geography): Revision Note
Exam code: 8035
Characteristics of hot deserts
Hot desert biomes are mostly found in a band around the Tropic of Cancer and Tropic of Capricorn
Approximately 20% of the Earth's surface is covered by hot desert ecosystems including in the following areas:
North America: The Mojave and Sonoran Deserts of the USA and Mexico
South America: The Sechura Desert in Peru and the Atacama Desert in Chile
Africa: The Sahara, Kalahari, Namib and Somali Deserts
Middle East: The Arabian Desert
Asia: The Dasht-e Lut in Iran, the Gobi, Turkestan, Thar and Taklamakan Deserts
Oceania: The Australian Deserts such as the Simpson and Great Victorian deserts
Hot desert characteristics
Location
15° - 30° north and south of the equator (tropical and sub-tropical)
North Africa - Sahara, Southern Africa - Kalahari and Namib, Australia. Middle East
Annual precipitation
Below 250mm
When rainfall does occur, it is often short torrential downpours
Temperature range
Daytime temperatures can reach 50°C but average around 25°C
Night-time temperatures below 0°C
Diurnal range is large up to 45°C
Annual range is around 15°C
Seasons
Summer and winter
Humidity
Low often between 10-30%
Soils
Tend to be saline - evaporation draws salts to the surface (salinisation)
Thin, sandy, grey and rocky
Contain little organic matter
Not very fertile
Biodiversity
Low biodiversity - 5000-6000 plant species, many invertebrates and up to 20 species of bird
Plants include cacti, yucca
Animals include spiders, scorpions, camels, lizards
Factors influencing the hot desert climate
High pressure all year which means the air is descending and warming so precipitation does not occur because the air is not rising
Prevailing winds are often from over land masses which means they contain little moisture
Some deserts are in a rain shadow so there is little rainfall
Cold ocean currents on the west side of continents may reduce summer temperatures due to the cooling effect of the ocean
Influence of pressure systems
Hot deserts form between 15°- 30° north and south of the equator as a result of the atmospheric pressure systems
Air rises at the equator and when it reaches the upper atmosphere it moves north and south
The air cools and starts to sink
This creates a zone of high pressure at about 30° north and south of the equator
Due to the sinking air, warm air cannot rise, condense and form clouds, resulting in high aridity
Humans
The edges of the desert are used for livestock herding
Communities such as the Bedouin are nomadic
Live in large open tents made from fabric woven from camel hair and vegetable fibres
Food sources are mainly from the animals that the Bedouin herd - goats and cattle
Headwear is worn to protect against the heat of the sun and sand
Restrictions on movements due to international borders have affected the Bedouin lifestyle
Many Bedouin are no longer nomadic and live in permanent settlements
Interdependence in a hot desert
All parts of the hot desert ecosystem are interdependent
A change in one part affects the others
Nutrient cycle
The growth of plants is limited due to the extremes of temperature and lack of water
The nutrient cycle is very slow
Most nutrients are stored in the soil
Due to a lack of organic matter the soils are coarse, sandy and low in nutrients
Plant and animal adaptations
Adaptations
To be able to survive the extreme temperatures and lack of rainfall the plants and animals are extremely well adapted
Plant adaptations
Low growing - this helps to avoid water loss due to strong winds
Shallow roots - these spread out near the surface to catch whatever rain falls
Thick stems - used to store water
Long roots - some plants have long tap roots instead of shallow roots to reach water deep underground
Small leaves or needles - the smaller surface area reduces water loss
Animal adaptations
Camels have a range of adaptations including:
Two sets of eyelashes and nostrils which close to keep sand out of their ears and noses
They also store fat in their humps so they can survive for long periods without food or water
Fennec Fox - have large ears which help them to lose heat
Burrowing - many animals burrow to avoid the intense day time heat
Insects and reptiles have waterproof skin to reduce water loss
Nocturnal - some animals hunt at night to avoid the daytime heat
Worked Example
Study Figure 1,
Plants and animals adapt in order to survive in a hostile environment.’
Explain this statement. Use either Figure 1 and your own understanding.
[6 marks]
Deserts are extreme environments with little precipitation (below 250 mm a year), high temperatures in the daytime up to 50 oC, and much cooler temperatures at night. This has led to low levels of biodiversity. The plants that survive there have a range of adaptations. The cacti in Figure 9 have spines instead of leaves and a thick waxy skin (E), which helps to reduce water loss [U]. They can also store water. Other plants have short life cycles and germinate, flower, and set seed in a short period of time after rainfall [U].
Animals also adapt well to harsh climates. Camels, as shown in Figure 9 have a range of adaptations, such as large, flat feet which make it easier for them to walk on sand (E). They can go without food and water for long periods as they lose little water through their urine and they have fatty humps which provide energy when food is unavailable (E). Other animals are adapted by being nocturnal or burrowing under the sand to avoid the heat [U].
Marking guidance
This is a 'Level of response' answer.
Each point made in the answer does not equal a mark.
The command word is 'explain' which means the answer needs to give an account of how plants and animals adapt together with evidence from the photographs.
Mark allocation
3 marks for evidence [E]
3 marks for understanding [U]
Common errors
The following errors mean that answers cannot achieve a Level 3 (top marks):
Not including information about both plant and animal adaptations.
Alternative content
The answer above is just one example of a response to this question. Other information which could be used in the answer includes:
Other plant adaptations
Long root systems
Small leaves
Slow growing
Other animal adaptations
Large surface area
Large ears to give off heatFennec Fox
Examiner Tips and Tricks
It is important to be clear about how adaptations help plants and animals survive in hot desert conditions. A common misconception is that camels store water in their humps when it is fat.
Biodiversity issues
Low levels of precipitation and high temperatures in many areas of hot deserts lead to low biodiversity
Where water is available there are higher levels of biodiversity
When rainfall does occur in desert areas a desert bloom may follow
Seeds and bulbs which have laid dormant germinate all at the same time
In the Atacama Desert desert blooms may occur between September and November when rainfall is unusually high
This can lead to over 200 species of flowers blooming, attracting insects and lizards
Threats to hot desert biodiversity are mainly human activities including:
Mining
Climate Change
Fuelwood gathering
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