Chapter 7
Ecology Notes
Voc. List: leaching, pavement, succulents, granivores, nocturnal, desertification, permafrost, active
layer, lichen, frost boils, subnivian, fellfields, modified hibernation, and migration
7.1: Deserts
Social Studies Link (on p. 111): Irrigation of desert soils has enabled some nations to turn
deserts into croplands. In the Middle East, for example, irrigation projects have turned the
Golan Heights into citrus orchards. Such projects require careful planning and management to
avoid draining water resources and accumulating salts in the soil.
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Common properties of a desert
The evaporation rate is high and exceeds rainfall-so very little rainfall
o Rarely 25 cm of precipitation in one year
 Usually less than 10 cm of rain per year
o Lack of rainfall is a limiting factor for desert biomes
Hot by the day and cool by night
Erosion in the desert: Water and Wind
Desert soils tend to be rich in minerals but poor in organic material
 Rainwater moving through soil carries minerals deeper into the soil by a process known
as leaching (water causes minerals to go out of the rocks, soil, and possibly organism
and go elsewhere)
o Very little rain forms in deserts so very little leaching occurs in the soil. As a
result, the upper layers of the desert soil become rich in minerals
Wind erosion occurs where loose dry desert soil and expose a lower layer of soil called
pavement-the desert floor (made of hard-baked sand, bare rock particles, or both)
Two Types of Deserts
1. Cool deserts-most located near the Arctic part of the world
 Cool temperatures during the day and can get to -100 o F at night
2. Hot and Dry deserts-most near the Tropic of Cancer or Tropics of Capricorn-near the
equator
 Can get to 120 o F during the day and can go down to 50’s or 60’s at night
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Types of plants and animals
Plants: Woody-stemmed and soft brittle-stemmed shrub plants and a wide variety of
other plants including cactus
 Cactus have spines that are actually considered leaves
 The spines reduce the loss of water by reducing the surface area from
which water can evaporate
The spines also protect cacti from being eaten
 Cactus also store liquid in their tissues
Plants such as cacti, are called succulents because they have thick,
water-filled tissues
a. The stored water allows plants in dry areas to survive
 Primary producers depend upon the availability of water
Animals and other organisms:
 Granivores are important herbivores of the desert ecosystem
Ex. Ants gather seeds underground
 All insects and reptiles have an outer coating that reduces water loss
 Most desert animals adapt to the heat
Rodents like kangaroo rats store their water in the form of urine
Most rodents and reptiles burrow in the ground during the
daylight and seek food at night-nocturnal
7.2: Formation of the Desert
 Deserts cover roughly 30% of the Earth’s surface and are found on every continent
except Antarctica
 Most deserts are found between 23.5oN (Tropic of Cancer) or S (Tropic of Capricorn)
 The location of the desert varies slightly from day to day because wind carries the sand
and the land formations trap the sand
People also cause deserts to form by desertification
 In this case, people over-farm and allow animals to graze too much losing the
nutrients, grass/crops.
7.3: Tundra
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Characteristics of Tundra Biomes
Tundra comes from the Finnish word “tunturi”-treeless heights
 Form in areas where temperatures are continuously too low to produce
photosynthesis (below 19.4oF (-7oC)) and long periods of low light or darkness
o Others factors that cause tundra areas: strong winds, abrasion (type of
wind erosion), and low precipitation
 Permafrost: permanent frozen layer of soil
o Most common in areas with a mean temperature of less than 27 oF (-3oC)
o All vegetation have to grow close to the ground surface
o Permafrost occurs in about 85% of Alaska’s surface area
 The soil above permafrost or bedrock is called the active layer
 Active layer becomes saturated like a wet sponge. The
results are: wetlands and freeze-thaw landforms
 Active layer thaws and refreezes every year-permafrost is
below
 Nutrients are low due to short growing season: Nitrogen is unavailable for N
cycle
 Most of the Earth’s tundra occurs in the Northern Hemisphere because of its
greater land mass.
 Lichen (pioneer species) is important to the Tundra
o A symbiotic relationship occurs between algae and fungi to produce
lichen.
 Lichen come in many forms and have no leaves, roots, stems, or
flowers. They do have colonies of delicate, hairlike filaments
(Some straight and some are branched).
o Lichen colonizes bare spots where soil does not exist. They produce acids
that dissolve rock, or other hard material to create soil. Lichen holds
water too. It traps windblown sand and plant debris to form a soil layer
that later forms moss, grasses, and larger plants
Two Types of Tundra
Arctic Tundra (also called High-latitude tundra, Lowland tundra, and Cold desert)
 Most are found at latitudes greater than 55 to 60 North degrees on
the coastal plains in the arctic regions of Siberia, northern Europe,
Canada, and Alaska
 The topsoil layer is made of fine sand or clay
o Frost boils occur by thawing and freezing water-filled soil
causing the movement of stones in lateral positions
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Peat formation occurs because slow decomposition rates and dead
organic material accumulates faster than it can be recycled (rate is
one meter per 1000 years)
o Peat bogs are a potential source of nutrients
 Water can’t drain away because permafrost is underneath, so
flatlands of the Arctic are wet and covered with shallow lakes
(kettle lakes) and bogs
o Permafrost in these areas can be a few inches to 2240 feet
below the surface
 Precipitation is often less than 5 inches (12.7 cm) per year
o Snow has very little moisture: 6-12 inches of snow with
wind drifts of 2-5 feet
o Rains occur mainly in August and September
 Temperatures
o Winter (October to end of April) can get down to -80oF
(Wind-chill: -120 oF)
 Little to no sunlight
o Spring (Occurs in May when the ice starts to crack-2 weeks)
up to 45oF
o Summer (Mid May to mid to late August) high temps in the
70’s
 Little to no darkness
o Fall (Sept) temps can reach down to 30oF –Snow starts
 Grassland and mixed shrub-land occur in the Arctic Summer
o Growing season is short (roughly 60 days) so plants such as
moss, shrubs, grasses, and small colorful wildflowers are
possible
 In the Summer-vegetable plants grow quickly and
came be larger than in other areas
o Trees get rough 1 meter tall and appear more like a scrub
than a tree
 The short growing season, limited space for roots to
grow (because permafrost is beneath the soil), and
strong winds cause dwarfed trees
Alpine Tundra (also called High-elevation tundra)
 Occur at high elevations at all latitudes (Mountainous areas)
including at the equator
 Known as the “Land of rocks”
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Have Fellfields-A Rock desert
Have more precipitation than Arctic tundra
o Hanging and Tidewater Glaciers occur in these areas
Able to withstand wind due to low and ground-hugging vegetation
Permafrost is absent or patchy because the shallow bedrock or
layers of rocks near the surface block water drainage-although
these areas can have similar landscape features as the Arctic
Tundra Animals
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Some animals change colors depending on the season
o Arctic fox and Arctic Owl
Small to medium animals are subnivian-burrow and lead active lives under the snow (an
insulator) during the winter
o Voles, shrews, lemming, and mice
Some animals hibernate: Arctic ground squirrels and marmots
o All hibernating animals must eat enough food (energy reserves-fat) during the
summer to maintain their body functions the rest of the year
o Modified hibernation-still sleep about 8 months, heart rate still slows but their
body temperature is not reduced: bears
Birds like ptarmigan (Alaska’s state bird) and grouse fold their winds and dive into loose
snow for protection
Many large animals in the Tundra migrate.
 Migration-Several of the same species traveling together in the search of food or
water
o Ex. Caribou (close relative of the reindeer) is a large migratory mammal
o Many birds and fish
Dateline 1974 (p. 116)
After several years of planning, construction began on the Alaska oil pipeline, which transports
oil 1285 km south from the North Slope of Alaska. The pipeline was completed three years
later. Because oil must be kept warm in order to flow, parts of the pipeline were constructed
above the ground to protect the permafrost from melting. To avoid interfering with migration
of caribou and other animals, the pipeline includes 400 raised sections for animal crossings.
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