DESERTS

A dry, barren area of land, especially one covered with sand.

A dry, often sandy region of little rainfall, extreme temperatures, and sparse vegetation.

A region so arid because of little rainfall that it supports only sparse and widely spaced vegetation or no vegetation at all

Can you name the top ten deserts in the world?

Here they are

1. DESERTS: ARE THEY ECOSYSTEMS OR BIOMES?

A biome is a collection of ecosystems that share the same climatic conditions. The rainfall, sunlight and temperature control how the biome is structured.

So, all the ecosystems of one type are called a biome.

There are many deserts across the world so deserts are a biome.

An ecosystem is a biological community of interdependent organisms and the physical environment they inhabit.

A desert is an ecosystem and because that ecosystem occurs on a worldwide level it is also a biome.

2. DESERTS: WHAT IS THEIR LOCATION AND WHY?

Deserts are found in bands at approximately 30 0 north and 300 south of the Equator, often along the two tropic lines.

Dry air descends (comes down to the ground) at the tropics. Dry air has little water in it was it lost it when it was over the tropics. Skies have few clouds so the heat from the day is lost at night.

3. DESERTS: WHAT IS THE CLIMATE LIKE?

Deserts have high day-time temperatures (450C plus) and low precipitation (less than 250mm/year)

Rainfall may be unevenly distributed between the months.

The lack of rain is usually the limiting factor in the desert that makes it unproductive.

4. DESERTS: WHY ARE THERE SO FEW PLANTS?

The lack of water means there is little photosynthesis so there is little plant growth.

Soils can be rich in nutrients as there is little rain to wash them away from the dead plants and animals, but low in organic matter.

Decomposition is slow as there is so little water.

5. DESERTS: HOW DO PLANTS SURVIVE?

Organisms have adapted to survive heat in the day and cold at night.

Xerophytes adapt to having little water by having few leaves to reduce transpiration (cacti). They store water in stems which can often expand.

Spines stop animals eating them and catch dew. Roots can be deep and they may have many

near the surface to absorb rain when it does fall.

6. DESERTS: HOW DO ANIMALS SURVIVE?

Mammals may live underground during the day. Many are nocturnal.

Snakes and reptiles are the commonest vertebrates. They conserve water and are cold-blooded which is suited to desert conditions.

7. DESERTS: ARE THEY OPEN, CLOSED OR ISOLATED SYSTEMS?

Open systems are where matter and energy are exchanged across the boundaries of the ecosystem.

In a desert sunlight comes in (energy) as does air (matter).

In closed systems energy is exchanged but not matter (the Earth).

Isolated systems have no exchange of energy or matter (the entire universe).

Deserts are therefore open systems

8. DESERTS: WHAT ARE THE BIOTIC AND ABIOTIC FACTORS OF A DESERT?

Deserts are characterised by little vegetation, high temperatures in the day, little rain and lots of sand.

Biotic features are plants and animals. Abiotic features include temperature,

light, soil particle size, soil drainage, soil mineral content, rainfall, wind speed.

9 A DESERTS: WHAT TROPHIC LEVELS EXIST IN A DESERT ECOSYSTEM?

A trophic level is the position an organism occupies in a food chain.

Mesquite bushes have seed pods that harvester ants like to eat. Horned lizards like to eat harvester ants. Hawks eat horned lizards.

Mesquite bushes are the producer. Harvester ants are herbivores and the primary consumer. Horned lizards and hawks are carnivores. Lizards are the secondary consumer and hawks are the tertiary

consumer.

Food chains rarely go above four trophic levels.

9B WHAT IS THE STRUCTURE OF A DESERT ECOSYSTEM?

Deserts have few trees. They have more low-lying bushes. Deserts have a variety of animal life

although numbers are often low as there is little vegetation to support the animal life.

10. DESERTS: HOW CAN A SPECIFIC LIZARD SPECIES BE IDENTIFIED FROM OTHER REPTILES AND AMPHIBIANS?

A key is used to identify species. A key usually has yes / no choices and so is called a

dichotomous key.

They have legs whereas other species may not. They have tails and other species may not.

Lizards may or may not have horns. They may have stripes or not. They may have a smooth skin or may have warts. They may be green or another colour. They may have a horn or no horn.

11. DESERTS: HOW DO THE FIRST AND SECOND LAWS OF THERMODYNAMICS EXIST IN THE DESERT?

The first law says that energy can neither be created nor destroyed.

In a desert ecosystem energy comes in from the sun, is changed by photosynthesis in plants to chemical energy and is passed on to herbivores as biomass.

It leaves the system as heat. No new energy has been created; it has just been transformed. This is about conservation of energy.

The second law says that energy goes from a concentrated form (the sun) to a dispersed form (in different animals and plants and waste and heat), and so for the living system to be maintained more energy is needed (from the sun).

This says energy is lost is a useable form and is about disorder or entropy.

Phew….

DESERTS: PLANET EARTHWATCH AND TAKE NOTES: remember notes must be connected to ESS

See how good your notes are by seeing how many of the questions that follow the film you can answer

AFTER WATCHING PLANET EARTH: What proportion of earth is desert? Hot and cold deserts: or both combined - Example: Temperature range: from to Difficulties for camels: Why is there so little water when there is so much

snow? How many are left? What makes the Gobi area a desert? Largest desert: Why do many animals live under the surface of the

desert?

How do kangaroos keep cool? 3 methods

So - how would deforestation affect the temperature of forest areas?

What do you know about the niche of the Fennec fox?

Driest desert in the world:

Where does the fog come from? ………………….. air meets ……………. air How do cacti survive with no rain? Draw a diagram to show the water

cycle in the Atacama coastal area Saguaro cactus – how does it survive? What are ‘leaves’ converted to and how

does this save water? How else do spines help cacti?

What are the ibex competing for? How does being the dominant male

help the ibex? Draw a pyramid of numbers for the

lizard and the black fly Elephants: carnivores / herbivores? Why are pride sizes so small?

Predator? Prey? Lion? Oryx? If the oryx population increased, what

would happen to the lion population? Then what would happen to the oryx population?

Positive feedback? Negative feedback? How do flash floods help the lions?

Hottest desert: Desert locust: herbivore/carnivore How does clumping help them?

And, finally, How are deserts both biomes and

ecosystems?

Are NPP rates high or low? Why? What is the level of biodiversity in a

desert compared to a rainforest? Why? Soils may be rich in nutrients – why

may this be connected with the lack of water?

Research the tri-cellular model to explain why there is so little rain in areas that become deserts and so much in areas that become rainforests.

Draw an annotated diagram to show your findings

Draw a food chain. Name and label the species.

Name the different trophic levels.