Deserts are dry ecosystems that receive very little rainfall. They occur in areas where evaporation exceeds precipitation due to various climatic factors like low humidity, high temperatures, and lack of cloud cover. Deserts are difficult places for humans and animals to live due to their unpredictable ecology and scarcity of resources. Desert plants and animals have developed various adaptations to survive the harsh and arid conditions like storing water, having waxy coatings or spines, and nocturnal behavior. True deserts receive less than 250mm of annual rainfall and support a diverse array of species that have adapted to the extreme environment.

1. Imagine a world where water is
in such short supply, and so
unpredictable, that it determines
the pattern of life. Not just
across the landscape, or
through the cycle of a year, but
across a decade, a century or a
millennium.

2. Desert
Caina, Maslog, Rustia

3. Deserts are difficult places for people because
of their dryness, their unpredictable
ecology, and also because they are patchy
environments — where food, water, and plants
are often concentrated in small pockets.
True deserts are ecosystems with sparse or no
vegetation due to low, infrequent and largely
unpredictable rainfall and often high
evaporation. Many deserts have high average
temperatures during the day and cool nights
due to no, or little, cloud.

4. What is a desert?
Land where evaporation exceeds rainfall
Dryness - a combination of low rainfall and
high water loss from evaporation, surface
run-off and seepage deep into the soil.
Low rainfall, high evaporation and a wide
daily range in temperature (hot by day-cool
by night due to low humidity)

5. Deserts occupy about 26 percent
of the continental area
Occur in two distinct belts
between 15 degrees and 35
degrees latitude in both the
Northern and Southern
Hemispheres – Tropic of Cancer
and Tropic of Capricorn

7. Why are deserts dry?
To understand why deserts are dry you
need to consider the water cycle.
On earth, water follows a path called the
water cycle. The sun’s energy heats water
making it evaporate from the land and sea.
As the water vapor rises it cools and forms
clouds. Wind may blow the clouds over
land and as the clouds are blown upward
over hills and mountains the water droplets
cool and fall as rain.

8. Low humidity allows up to 90% of
solar radiation to penetrate the
atmosphere and heat the ground. At
night, the desert yields the
accumulated heat back to the
atmosphere
Rain, when it falls, is often heavy and
unable to soak into the dry
earth, rushes off in torrents to basins
below

9. Average Rain Fall
500mm  arid-like conditions if
the temperature and evaporation
rates are high
250-350mm  semi-arid/semi-
desert
<250mm  arid
<100mm  true deserts
<70mm  extreme deserts

10. How are deserts formed?
Movement of air masses
High pressure area alters the
course of rain, deflects
rainstorms preventing moisture
from reaching certain areas
Winds blowing over cold waters
become cold  carry little
moisture & produce little rain

11. How are deserts formed?
Mountain ranges
 Forms rain shadow
 A rain shadow is an area of dry land that lies on the
leeward (or downwind) side of a mountain. Winds carry air
masses up and over the mountain range and as the air is
driven upward over the mountain, falling temperatures
cause the air to lose much of its moisture as precipitation.
Upon reaching the leeward side of the mountain, the dry
air descends and picks up any available moisture from the
landscape below. The resulting profile of precipitation
across the mountain is such that rainfall and moist air
prevails on the windward side of a mountain range while
arid, moisture-poor air prevails on the leeward side of the
mountain range.

14. Examples:
 The Gobi Desert lies in the rain shadow of the
Himalayas.
 The Atacama Desert lies in the rain shadow of the
Andes.
 The Patagonia region lies in the rain shadow of the
Andes.
 Death Valley lies in the rain shadow of the Pacific Coast
Ranges of California and the Sierra Nevada Mountains.
 The city of Spokane in the state of Washington lies in
the rain shadow of the Cascade Mountain Range
(Spokane receives little rainfall). Seattle, Washington
lies on the windward side of the Cascades (it receives
generous amounts of rainfall).

15. Types of Deserts
Deserts come in all shapes and sizes
and there are lots of different ways of
looking at them – location, climate,
ground cover and main types of plants
We usually think of deserts as being
hot but this is not always the case.
There are also cold, coastal and
semiarid deserts.

16. Hot Deserts
located near the equator. Day
temperatures can reach more than
38ºC but the nights are usually very
cold.
generally have no cloud cover 
allows them to heat up and cool down
very quickly.
Great Sandy Desert / Simpson Desert

18. Cold Deserts
are found further from the equator and are
usually in the centre of continents. They are
often high in mountainous areas. In
winter, these deserts can be covered with
snow and ice. The Patagonian Desert in
Argentina, South Antarctica is also an
extreme example of a cold desert.

20. Coastal deserts
are found on the west coast of
continents. They have warm summers
and cool winters and are often called
cool deserts.

21. Coastal deserts by the sea
Water does not evaporate from a cold
ocean as quickly as it does when the
water is warm. Air blown onto the coast
from a cold ocean contains no moisture
to fall as rain. During the day, water
evaporates from the land further helping
to make a desert. At night the land cools
and some of the moisture in the air
above the land condenses to form fog.

23. Semiarid deserts
receive between 250mm and 350mm of
rain. The summers are long and dry
with moderate temperatures between
20°C and 30°C. Any rain usually falls in
the winter months. Over one-third of
Australia is semiarid desert.

25. Biotic

26. Plants
•Desert Plants are exposed to extreme temperatures and
drought conditions.
• Plants must cope with extensive water loss.
How do you think plants grow in a place
that is very, very dry?

27. Hot and dry desert
oSome plants have no leaves or small seasonal leaves
that only grow after it rains.
-The lack of leaves helps reduce water loss during
photosynthesis. Leafless plants conduct photosynthesis in
their green stems.
Cactus Garden Asparagus

28. Some plants, called succulents, store water in their
stems or leaves;
The storage of water often
gives succulent plants a
more swollen or fleshy
appearance than other
plants
Salicornia

29. Long root systems spread out wide or go deep into the
ground to absorb water;
The roots collect water after
rain. Stored in the pleated
expandable stem, the water
keeps the saguaro alive until
the next rain.
Saguaro

30.  Plant drought-evaders flower only in the presence of
moisture
They persist as seeds during
drought periods, ready to
sprout, flower, and produce
seeds when moisture and
temperature are favorable.
Morman tea

31. Semi arid desert
Spines to discourage animals from eating plants for
water;
Since many desert
plants store water in
their spongy tissue,
animals will eat them
for the moisture. The
thorns keep them safe
from many animal
predators.
Prickly pear cactus

32. Leaves with hair help shade the plant, reducing water
loss
The most striking feature is the
long, white hairs it
possesses, which serve to
protect it from the sun.
Old Man Cactus

33. Waxy coating on stems and leaves help reduce water loss.
-The waxy surface of
the aloe plant acts like
a plastic
wrapper, keeping
precious water inside.
-Glossy leaves reflect
the sun's
rays, reducing leaf
temperatures and
evaporation rates.
Aloe

34. Coastal desert
oplants with thick and fleshy leaves or stems can take
in large quantities of water when it is available and
store it for future use.
oSome plants have extensive root systems close to
the surface where they can take advantage of any rain
showers.

35. Buckwheat bush Saltbush

36. Cold desert
o The plants are widely scattered.
o Plant heights vary between 15 cm and 122 cm.
o The main plants are deciduous, most having
spiny leaves.

37. Animals
In spite of their aridity, desert ecosystems support
a surprising diversity of animal life, including a wide
assortment of
beetles, ants, locusts, lizards, snakes, birds, and
mammals.

38.  The mammals are notably herbivores
- They consume a wide range of species, plant
types
They feed on succulents when
available and then switch to
woody browse during the dry
periods
Desert Bighorn sheep

39. Desert carnivores, are opportunistic feeders;
most of them have mixed diets that include
leaves and fruits
Small herbivores—the desert
rodents, particularly the ants tend to be
granivores, feeding largely on seeds
Omnivory seems to be the rule in desert
ecosystems

40. Hot and dry desert
oThe animals include small nocturnal (active at night)
carnivores.
oThe animals stay inactive in protected hideaways
during the hot day and come out to forage at
dusk, dawn or at night, when the desert is cooler.

41. Animals make burrows to escape the heat
-Kangaroo rats dig
burrows to protect
themselves from predators
and heat.
-Kangaroo Rats are
nocturnal (avoiding the
heat during the day).
Kangaroo rat

42. Semi arid desert
oDuring the day, insects move around twigs to
stay on the shady side;
ojack rabbits follow
the moving shadow of
a cactus or shrub.

43. large ears, long legs, Pale-colored fur and
feathers
Large ears:
-are densely lined with
shallow blood
vessels, allowing air to cool
their blood as it circulates.
Jackrabbit

44. Coastal desert
Aestivation -during hot dry spells, the spade-
foot toad (Scaphiopus sp.) covers
itself with a substance to stay
moist and then enters an
underground burrow, where it
can survive for many months
until heavy rains signal it to
wake.
-After mating and laying eggs in
temporary pools, the toads
return to their burrows and
resume estivation until the next
Spadefoot toad heavy rains.

45. Other adaptations:
Long legs :
Some small creatures, such as
beetles and lizards, reduce the
amount of heat they absorb from
the desert surface by having
long legs to keep them high up
and to disperse heat.
Pale-colored Fur and Feathers:
- help others to keep cool by reflecting
sunlight.

46. some desert animals have concentrated the
body's fat in one place, such as a hump or tail
-This animal has the ability to
store large amounts of water
for a long time, and because of
that, it is able to survive in the
dry and harsh desert.
-These animals have
transparent eyelids which
enable them to keep sand out of
their eyes.
Camel

47. Tolerate Hyperthermia
Some animals can survive body
temperatures that would be
dangerous to humans
(e.g., this antelope
squirrel tolerates body
temperatures over 104 degrees
Farenheit).
Antelope squirrel

48. Where do animals in the desert get
their water from?
Since water is so scarce, most desert
animals get their water from the food they
eat:
•succulent plants,
•seeds, or
•the blood and body tissues of their prey.

49. How do desert animals prevent
water from leaving their bodies?
-Desert animals prevent water leaving their bodies in a
number of different ways. Some, like kangaroo rats and
lizards, live in burrows which do not get too hot or too cold
and have more humid (damp) air inside.
-Other animals have bodies designed to save water.
Scorpions and wolf spiders have a thick outer
covering which reduces moisture loss. The kidneys of desert
animals concentrate urine, so that they excrete less water.

50. Abiotic
• Rainfall
• One of the most distinct abiotic factors in a desert is the
amount of rain that falls per year. Typically, deserts receive
less than 20 inches of rain per year. This means that animals
and plants looking to survive in the desert must be able to live
with little water for extended periods of time. For example,
cacti have evolved to store water in their stems to help them
through dry spells.

51. •Temperature
Deserts typically go through huge fluctuations in
temperature during a 24-hour period. Because there is
little moisture, deserts lack the insulating protection of
both humidity and cloud cover. A desert that is hot during
the day may drop to well below zero degrees at night, once
the heat of the sun has left. Organisms that cannot adapt
well to rapid temperature fluctuations have trouble
surviving in the desert.

52. • Soil
• The type of soil in an ecosystem determines what plants
can grow, which in turn defines which animals can
survive. Desert soil types can vary greatly, but most have
excellent drainage. This means that the soil is loose
instead of compacted. When rain does fall in the
desert, it seeps quickly into the soil. Rapid drainage can
have the side effect of washing nutrients out of the soil.

53. • Light
• Because deserts typically don't have many shade-giving
plants, almost all of their surface area is given full
exposure to direct sunlight during the day. Extreme light
exposure limits the types of plants that can grow in the
desert, and makes it difficult for many animals to see.
Imagine being surrounded by light-colored soil on a very
bright day. It might be blinding. This may be one reason
that so many animals in the desert are nocturnal.

54. Human Impact on deserts
• Deserts are being destroyed by development. Some build industries and
factories in the deserts. Many people also think the deserts sunny weather
is a perfect reason to build a home there.
• As populations in desert cities rise, so does the demand for water.
• Many desert streams, rivers, and lakes once used by animals have been
drained for industries, people, and farms.

55. • Another simple activity is Off roading.
• Their vehicles leave tracks on the soil, which will scar the land for decades.
• These tracks also kill off vegetation, when vegetation is harmed, so are the
animals.

56. • Animals that hide in the sand can also be harmed. The sand viper, which
hides so well in the soil, can become an accidental victim of off roading
mayhem.

57. • Animal and plant collectors have also devastated the desert. People who
collect rare species of cacti have completely wiped out entire populations.
• Chuckwalla lizards have also been targeted to be sold in the pet trade.
Their numbers have also been reduced dramatically.

58. • Mining - not only do the mining operations themselves disturb the desert
habitat and plants and animals that live there, the roads built to get
needed equipment into the mines also destroy the desert. Uranium
mining creates a host of radioactive hazard.

59. • Ranching - overgrazing is one of the major threats to the desert habitat.
Mismanagement and overuse of land is putting severe pressure on desert
habitat areas.
• Farming - as the population on our planet continues to increase at an
alarming rate,the demand for more agricultural products, needed to feed
these billions of people, will also increase. With modern technology, it is
becoming increasingly easier to turn dry, arid desert habitat into
productive farmland.

60. • Deserts are being used as dump sites for nuclear waste and as nuclear
testing grounds. Recently, a site was opened in the desert of New mexico
to be used for the storage of nuclear waste.