Most of the year the desert looks lifeless. But when rainy
season comes, the land explodes with life. Plants and animals hurry
to feed, grow and reproduce. When the rain is done life seems to
disappear again, until the next rainy season. This occurs in the
desert and in the tundra, but in the tundra, it occurs in the short
summer.
Slide 3
I CAN Describe the characteristics of a desert. Explain how
desert organisms are adapted to live in their environment.
Slide 4
Deserts The one thing in common that all deserts have is the
lack of water.
Slide 5
DESERT SOIL Desert soils are usually poor in organic materials.
Rainwater moving through the soil carries minerals deeper into the
soil in a process called leaching. However, because there is not
much rain, there is not much leaching.
Slide 6
DESERT SOIL The lack of rainfall tends to prevent plants from
growing. The decay of organic material is also slowed by the small
amounts of precipitation. With the very little decaying material
and little rain, there is not much topsoil.
Slide 7
DESERT SOIL Loose, dry desert soil is easily blown away by the
wind. If the loose soil is removed, a lower layer of soil called
pavement is exposed. Pavement is the desert floor, made mostly of
hard-baked sand and/or bare rock.
Slide 8
DESERTS IN THE US There are 2 types of deserts in the US. Cool
deserts and hot deserts There is a variation because of the
elevation and latitude.
Slide 9
DESERTS IN THE US Cool deserts are located on the Eastern side
of the Sierra Nevada and Rocky Mountains. Hot deserts are located
in the southwest, specifically, Arizona, New Mexico, and western
Texas. Cool deserts have sagebrush, while hot deserts have
cacti.
Slide 10
DESERT CLIMATE Deserts rarely get more than 25 cm (10 inches)
of precipitation. The amount of precipitation determines the types
of plants that live there, and the plants determine what types of
animals live in the area. The lack of rainfall is therefore the
limiting factor in the desert biome. Most of the rain in the desert
falls in short thunderstorms.
Slide 11
DESERT CLIMATE Desert pavement is very dry and compacted, so
when it does rain, the rain usually runs off rather than being
absorbed into the ground. The lack of moisture also affects
temperatures. Moisture tends to help act like a blanket to hold in
heat. Since there is little moisture, temperatures can rise and
fall dramatically, swinging from hot days to very cold nights.
Slide 12
DESERT ORGANISMS Organisms that live in the desert are adapted
to live with little water and extreme temperatures. Some
adaptations involve physical structures, while others involve
behaviors.
Slide 13
DESERT PLANTS Plants that live in the desert must be able to
absorb water from the ground and prevent the loss of water from
their tissues. Spines of cacti are one adaptation to reduce the
loss of water from the plant. The spines are the leaves of the
plant, and with little surface area they reduce the amount of water
that can evaporate from them.
Slide 14
DESERT PLANTS Cacti can also store water in their tissues.
Plants that have thick, water filled tissues are called succulents.
This stored water allows plants to live for a long time during dry
periods. The stored water also makes these plants attractive to
desert animals.
Slide 15
DESERT PLANTS Cacti are only native to the American continents,
but other succulents are found in other deserts. Aloe vera is one
example of a succulent found in Africa Adaptations are also
apparent when looking at the roots of desert plants. Plant roots
tend to be very shallow, yet wide, or extremely deep (20m)
Slide 16
DESERT ANIMALS Most desert animals get the water they need from
their food. All insects and reptiles in the desert have outer
coatings that reduce water loss. The shells of insects and the
scales of retiles evolved to survive the life in the desert.
Another desert adaptation that several mammals have is to be
nocturnal, or be active at night.
Slide 17
I CAN Illustrate the processes that cause deserts to form.
Slide 18
FORMATION OF DESERTS Deserts are found on every continent
except Antarctica. Most deserts lie within two belts on the Earth
known as the desert belts. They are at approximately 30 degrees
north and south of the equator.
Slide 19
NATURAL DESERT FORMATION Near the equator the air is warmest,
and rises. As it rises it cools, and sinks back down to the Earth
at about 30 degrees N and S of the Equator. It warms as it sinks,
and thus creates the deserts.
Slide 20
NATURAL DESERT FORMATION In the US, deserts are rain shadow
deserts. The air is forced up mountains, forced to cool, water
vapor condenses, it rains, and then the air is dry moving back down
the other side of the mountain.
Slide 21
NATURAL DESERT FORMATION Some deserts are semiarid deserts,
meaning that they are dry, but not as dry as a textbook
desert.
Slide 22
DESERTIFICATION Deserts are often bordered by semiarid regions.
Human activities have cause many semiarid regions to become
deserts. The transformation of semiarid land to desert is called
desertification. It can be caused by too much grazing, which leads
to topsoil erosion. This has occurred on every continent but
Antarctica. An area the size of Maine turns into desert each
year.
Slide 23
I CAN Describe why the characteristics of the tundra make it a
fragile ecosystem. Compare the characteristics of tundra organisms
with those of their relatives in warmer climates.
Slide 24
TUNDRA The tundra is a cold, windy, dry region. It is just
south of the polar ice caps in Alaska, Canada, Greenland, Iceland,
Scandinavia, and Russia. In the S. hemisphere this area is covered
by oceans. The tundra is one of the largest biomes, covering 10% of
Earths surface. However it has the fewest organisms, making it
extremely fragile.
Slide 25
TUNDRA CLIMATE Like the desert, the tundra receives little
precipitation. The main difference between deserts and tundra is
the temperature. Most precipitation falls as ice or snow, and temps
are below freezing almost all year. Temperature is the limiting
factor here.
Slide 26
TUNDRA CLIMATE Summer days are long and cool, and only the top
layer of soil will thaw in the summer months. The soil beneath the
active (thawed) zone is called permafrost because it is permanently
frozen. Mats of grasses, mosses, and other plant life covers the
ground in the summer. The growing season is extremely short.
Slide 27
TUNDRA CLIMATE Vegetation does not recover quickly from
distruption. When it does rain, the water forms bogs and marshes at
the surface, which attracts mosquitos and black flies. These
insects are an important link in the food chain in the tundra. If
the permafrost melts, the water will drain, and affect the first
stages of the food webs.
Slide 28
TUNDRA PLANTS The growing season is about 60 days in the
tundra. The tundra plants tend to be small and grow close to the
ground. Root systems are shallow because they cannot penetrate the
permafrost. Trees are smaller and look more like shrubs. Plants are
dwarfed by the short growing season and strong polar winds.
Slide 29
TUNDRA ANIMALS Many of the animals in the tundra are seasonal,
that is, they migrate there only for breeding or raising of young.
There are few predators in the tundra. Migratory birds come to feed
on the insects, and serve as prey for foxes and other migratory
predators. There are no reptiles or amphibians.
Slide 30
TUNDRA ANIMALS Caribou are a large migratory mammal that also
lives in the tundra part of the year. Like many tundra animals,
caribou have thick coats with hairs that are filled with air to act
like insulation. Caribou fill the tundra each year to eat the
lichens. Many are disappearing due to loss of lichens and
interference with their migratory routes.
Slide 31
TUNDRA ANIMALS Some of the mammals in the tundra are year
around residents. The arctic fox, musk oxen, polar bears (on the
coasts), and wolverines are all year around dwellers. The fox hunts
birds and buries them in the permafrost to eat during the
winter.