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Unit 3 – Ecosystems
Food Chains & Food Webs
Ecosystem Basics
Ecosystem: the network of relationships among plants, animals and the nonliving constituents in an environment.
View figure 6.3 on page 94 of your text and you can see that there are a lot
of living things (plants & animals) and non-living things (soil, water sun,
temperature etc.) that affect each other. It is the system of relationships
between the organisms and between the organisms and the non-living
environment that makes up the ecosystem.
Organisms in an Ecosystem
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Producer: a plant which can synthesize carbohydrates using carbon
dioxide and the sun’s energy.
o for example in figure 6.3 on page 94 all the plants, like Duck
weed, Willow, cat tails etc. are producers and convert the sun's
energy into carbohydrates (food energy) for all other organisms
in the ecosystem.
o Producers are so named because they actually produce the food
for the ecosystem.
Consumers: All those organisms in trophic levels other than
producers. Consumers eat their food.
o For example in figure 6.3 on page 94 all the animals, Raccoon,
bass, duck etc. are consumers.
o Consumers are so named because they have to eat or consume
their food.
o 1st-order or primary consumers eat producers.
o 2nd-order or secondary consumers eat primary consumers.
o 3rd-order or tertiary consumers eat secondary consumers.
Decomposers: Simple organisms that obtain their food from dead
organisms and wastes.
o For example in Figure 6.3 on page 94 of your text the colony of
bacteria, protozoa, and flatworms are all decomposers.
o Decomposers are so named because they are actually
responsible for decomposing dead organisms.
Similarities—all three are terms referring to the way organisms obtain
food & energy
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Differences—the way they obtain food. Producers make it, consumers
eat it, decomposers feed on wastes & dead material.
Food Chains & Food Webs
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Food chain: linear sequence representing the flow of energy &
nutrients from the simplest plant to the top carnivore.
o an example of a food chain from fig. 6.4. P. 95
o Tree  insect  insect-eating bird  hawk
o Producer: Tree
o 1st-order consumer: insect
o 2nd-order consumer: insect eating bird
o 3rd-order consumer: hawk
Food web: a series of interconnecting food chains in an ecosystem.
o Figure 6.4 on page 95 of your text book depicts a food web in a
temperate deciduous forest.
Similarity—both food chains and food webs show the flow of nutrients
and energy in an ecosystem.
Differences—Food webs are: more complex; composed of several food
chains; a more realistic picture of an ecosystem.
Energy Flow in an Ecosystem
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Using figure 6.5 on page 95 you can summarize the main energy flows
in an ecosystem:
o the Sun is the source of all ecosystem energy;
o producers make food via photosynthesis;
o consumers eat plants and other consumers to get energy;
o each time energy moves from one organism to another, energy
leaves the system in the form of heat;
o decomposers return nutrients to the soil but energy is not
recycled.
Assigned Readings
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"The Web of Life" on pages 92-93 of your text book.
"Food Relationships in Ecosystems" on pages 93-94 of your text book.
"Energy levels in food chains" on pages 94-95 of your text book.
Test yourself
1. A/n _?_ is the network of relationships among plants, animals and the
non-living constituents in an environment.
2. A/n _?_ is a plant which can synthesize carbohydrates using carbon
dioxide and the sun’s energy.
3. _?_ are all those organisms in trophic levels other than producers.
These organisms eat their food.
4. _?_ are simple organisms that obtain their food from dead organisms
and wastes.
5. _?_ are consumers that eat producers.
6. _?_ are consumers that eat Primary consumers.
7. _?_ are consumers that eat secondary consumers.
8. View figure 6.3 on page 94 of your text and name one Producer.
9. View figure 6.3 on page 94 of your text and name one Primary
Consumer.
10.View figure 6.3 on page 94 of your text and name one secondary
consumer
11.What is the original source of all energy for an ecosystem?
12.A/n _?_ is a linear sequence representing the flow of energy &
nutrients from the simplest plant to the top carnivore.
13.A/n _?_ is a series of interconnecting food chains in an ecosystem.
14.Do decomposers recycle energy and nutrients in an ecosystem?
15.When energy is passed from one feeding level to the next energy is
lost. In what form is the energy lost?
Answers
1. A/n _?_ is the network of relationships among plants, animals and the
non-living constituents in an environment. ECOSYSTEM
2. A/n _?_ is a plant which can synthesize carbohydrates using carbon
dioxide and the sun’s energy. PRODUCER
3. _?_ are all those organisms in trophic levels other than producers.
These organisms eat their food. CONSUMERS
4. _?_ are simple organisms that obtain their food from dead organisms
and wastes. DECOMPOSERS
5. _?_ are consumers that eat producers. PRIMARY CONSUMERS OR 1ST
ORDER CONSUMERS
6. _?_ are consumers that eat Primary consumers. SECONDARY
CONSUMERS OR 2ND ORDER CONSUMERS
7. _?_ are consumers that eat secondary consumers. TERTIARY
CONSUMERS OR 3RD ORDER CONSUMERS
8. View figure 6.3 on page 94 of your text and name one Producer. TREE
9. View figure 6.3 on page 94 of your text and name one Primary
Consumer. HONEY EATER OR INSECT OR FROG
10.View figure 6.3 on page 94 of your text and name one secondary
consumer SNAKE OR INSECT EATER OR HAWK
11.What is the original source of all energy for an ecosystem? SUN
12.A/n _?_ is a linear sequence representing the flow of energy &
nutrients from the simplest plant to the top carnivore. FOOD CHAIN
13.A/n _?_ is a series of interconnecting food chains in an ecosystem.
FOOD WEB
14.Do decomposers recycle energy and nutrients in an ecosystem? NO,
THEY DO RECYCLE NUTRIENTS BUT ENERGY IS NOT RECYCLED, A
CONSTANT INPUT OF SUN IS REQUIRED
15.When energy is passed from one feeding level to the next energy is
lost. In what form is the energy lost? HEAT
Ecosystem Balance & Food Pyramids
Food Pyramids
Food Pyramids
Food Pyramid:
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is a diagram showing each trophic level as a horizontal bar;
producers are located on bottom & higher trophic levels are placed on
top of each other;
each bar is drawn in proportion to the mass of organisms, giving the
triangle shape.
Pyramid of Numbers:
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There are fewer organisms at each increasing trophic level:
o less energy available at each increasing level;
o fewer organisms can obtain energy to live;
o therefore fewer organisms at increasing levels.
Pyramid of Energy:
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There is a high degree of energy loss at each trophic level.
o The producers only store 1% of the sun's energy as food
energy.
o Each consumer level looses energy for several reasons:
 much of the energy is lost as heat;
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o
If we
1000
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most of the energy is used to carry out life functions—ie.
we burn many calories of energy each day. so do all
organisms;
if an organism dies without being eaten the energy goes
to the decomposers and not up the trophic levels;
consequently only about 10-15% of the energy is stored
as usable food energy at each level..
look at this in terms of units of energy and we start with
units of energy at the producer level then:
the primary consumers would only have 100-150 units of
food energy stored for the next level;
the secondary consumers would only have 10-15 units of
food energy stored for the next trophic level;
the tertiary consumers would only have 1-1.5 units of
food energy stored as food energy—it is easy to see why
we do not often see a quaternary trophic level
Magnification of Toxin Levels
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Biological Amplification is the term used to describe the fact that
higher trophic level receive a higher dose of food chain toxins.
This problem has occurred in our environment. The most common case
was that of DDT which was used to control insect populations
o DDT was a particularly dangerous toxin because it is fat soluble
and stays in an animal's fat. (Some poisons are water soluble
and can be excreted from the system.)
o Lower order organisms ingest some poison which may or may
not affect them.
o Higher order organisms eat large numbers of lower order
organisms. A small amount in a frog becomes large in a hawk
that eats 100 frogs.
Assigned Readings
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"Food pyramids" on pages 95-97 of your text book.
Assigned Activities
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Complete question #11 on page 97 of your text book.
Test yourself
1. What term is given to a diagram showing each trophic level as a
horizontal bar where producers are located on bottom & higher trophic
levels are placed on top of each other.
2. Which level of a food Pyramid has the most food energy?
3. Which level of a food Pyramid has the least food energy?
4. Which level of a food Pyramid has the largest number of individuals?
5. Which level of a food Pyramid has the smallest number of individuals?
6. Which level of a food Pyramid is most in danger because of toxin
magnification.
7. What % of energy in a trophic level is passed onto the next level?
8. What causes the loss of energy between trophic levels?
9. What term is given to the fact that higher trophic level receive higher
doses of food chain toxins?
Answers
1. What term is given to a diagram showing each trophic level as a
horizontal bar where producers are located on bottom & higher trophic
levels are placed on top of each other. FOOD PYRAMID
2. Which level of a food Pyramid has the most food energy? BOTTOM
(PRODUCERS)
3. Which level of a food Pyramid has the least food energy? TOP (THIRD
ORDER CONSUMERS)
4. Which level of a food Pyramid has the largest number of individuals?
BOTTOM (PRODUCERS)
5. Which level of a food Pyramid has the smallest number of individuals?
TOP (THIRD ORDER CONSUMERS)
6. Which level of a food Pyramid is most in danger because of toxin
magnification. TOP (THIRD ORDER CONSUMERS)
7. What % of energy in a trophic level is passed onto the next level? 1015%
8. What causes the loss of energy between trophic levels? ENERGY USED
TO CARRY OUT LIFE PROCESSES & ORGANISMS NOT EATEN BY THE
NEXT TROPHIC LEVEL
9. What term is given to the fact that higher trophic level receive higher
doses of food chain toxins? BIOLOGICAL AMPLIFICATION
Upsetting the Balance Lab
Ecosystems are in a very delicate balance. Changing one thing in the
ecosystem will have a domino effect through the system because of the
relationships that exist.
There are several good questions in your text that address this issue. They
ask you to analyze the current relationships in the ecosystem and then
determine the effect of changing one relationship.
Question #13 on page 98 is about a pond ecosystem with blue gill sunfish.
This is a sample question. Any question could be asked where we have to
predict possible outcomes. Read the question (#13 on page 98) and see
what you think would happen. Use your background knowledge that there
are inter-relationships in all ecosystems. Then click here to get one person's
perspective on the possible changes. Remember experts differ on the
possible impacts in real situations. However they all make sound arguments
based on inter-relationships.
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Sun fish move to reeds
Plankton pop. Decrease
Sun fish decrease in size
Larvae pop. increase
Lesson title here
The introduction of Large mouth bass would cause:
1. Sun fish move to reeds to escape predation by the large mouth bass
2. The Plankton population might decrease because the bluegill sunfish
would be feeding on them more now that they can not stay in the
open and eat the larva
3. The Sun fish might decrease in size and abundance because the
plankton is not as full of energy.
4. The Larvae population might increase due to less feeding by the sun
fish.
Assigned Activities
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Click on "Balance in the Ecosystem" Lab open it, print it and complete
it.
World Ecosystems
High Latitude Ecosystems
Climax Vegetation
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Climax Vegetation is the natural vegetation in the last possible stage
of vegetation development.
Climax vegetation is stable and in balance with the climatic conditions.
It should change very little if left undisturbed.
Ecosystems are largely defined by the climax vegetation that grows in
it. The type of vegetation is largely determined by the climate.
We will look at three major type of ecosystems found in high latitude
regions. Look at figure 6.8 on page 102 of your text book and you will
see the variety of ecosystems in the world.
Coniferous (Boreal) Forests
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The climax vegetation in coniferous forest is Evergreen trees with:
o needle-like leaves;
o thick bark;
o conical shape;
o dense growing which blocks sun.
The location of the Boreal forest can be seen by Analyzing the world
ecosystem map (figure 6.8) on page 102. It is found only in the
northern hemisphere and is located in a broad band across Northern
North America and Northern Eurasia.
Coniferous trees are well adapted to lack of water in winter (it is all
frozen):
o needle leaves reduce surface area for transpiration;
o drooping branches and conical shape allow heavy snow to fall off
relieving the pressure;
o thick bark reduces water loss.
The climate in the boreal forest is temperate cold winter. Look at
figure 6.8 on page 102 and locate the boreal forest; then turn to page
75 and locate the temperate cold winter (subarctic) climate region. the
two match very closely.
Tundra
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The climax vegetation in the Tundra is grasses, shrubs and low plants
with:
o shallow roots;
o fast reproduction/flowering cycles.
The location of the Tundra can be seen by Analyzing the world
ecosystem map (figure 6.8) on page 102. It is found only in the
northern hemisphere and is located north of the Boreal forest across
Northern North America and Northern Eurasia.
The shrubs and bushes are well adapted to the extreme climate of the
north where winter is long and summer is very short:
o shallow roots are needed because 1-3 meters below the surface
the soil is completely frozen (Permafrost);
o the fast flowering and reproduction cycle is needed because the
growing season is very short, lasting only 1-2 months.
Animals have a variety of adaptations to the harsh Tundra climate.
o hibernation from the cold winter;
o migration in for the summer season and out for the winter
season is a common strategy for Birds and even larger animals
like caribou;
o the development of insulating features like thick fur & fat
insulation is common among polar bears and other mammals;
o white fur/feathers to help with camouflage is another common
adaptation.
The climate in the Tundra is so definitive of the tundra that it is called
Tundra climate. Look at figure 6.8 on page 102 and locate the Tundra;
then turn to page 75 and locate the Polar (Tundra) climate region. the
two match very closely.
Polar Ice Caps
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The climax vegetation in the Polar Ice Cap is Phytoplankton beneath
the ice.
The location of the Polar Ice Caps can be seen by Analyzing the world
ecosystem map (figure 6.8) on page 102. It is found only in both
hemispheres and is located only in the extremely high latitudes.
The adaptation of producers to this ecosystem is extreme. There is no
land for the producers to grow in so there are only small
phytoplankton to form the base of the food chain.
Animals have a variety of adaptations to the harsh Polar ice cap
climate.
o migration in for the summer season and out for the winter
season is a common strategy for Birds and even larger animals
like caribou;
o the development of insulating features like thick fur & fat
insulation is common among polar bears and other mammals;
white fur/feathers to help with camouflage is another common
adaptation.
The climate in the Polar ice cap is so definitive of the Polar ice cap that
it is called Polar (ice cap) climate. Look at figure 6.8 on page 102 and
locate the Polar ice cap; then turn to page 75 and locate the Polar (Ice
cap) climate region. the two match very closely.
o
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Assigned Readings
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"Ecosystems Throughout the World" on pages 101-102 of your text.
Assigned Activities
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Complete Question #19 on page 102 of your text book.
Test yourself
1. What name is given to the natural vegetation in the last possible stage
of vegetation development. this vegetation is stable and in balance
with the climatic conditions.
2. Name three major high latitude ecosystems types.
3. What is the climax vegetation of the Boreal Forest?
4. What is another name for the Boreal Forest?
5. Name one adaptation organisms have in the Boreal forest.
6. What type of climate does the boreal forest experience?
7. What is the climax vegetation in the Tundra?
8. What type of climate does the Tundra experience?
9. Name one adaptation organisms have in the tundra.
10.What producer forms the base of the ecosystem in the polar ice caps?
11.What climate does the polar ice cap ecosystem receive?
12. Name one high latitude ecosystem the is located in both hemispheres.
Answers
1. What name is given to the natural vegetation in the last possible stage
of vegetation development. This vegetation is stable and in balance
with the climatic conditions. CLIMAX VEGETATION
2. Name three major high latitude ecosystems types. BOREAL FOREST,
TUNDRA, POLAR ICE CAP
3. What is the climax vegetation of the Boreal Forest?
CONIFEROUS/EVERGREEN TREES
4. What is another name for the Boreal Forest? CONIFEROUS FOREST
5. Name one adaptation organisms have in the Boreal forest.
6. Needle leaves reduce surface area for transpiration
7. Drooping branches and conical shape allow heavy snow to fall off
relieving the pressure
8. Thick bark reduces water loss.
9. What type of climate does the boreal forest experience? TEMPERATE
COLD WINTER (SUB ARCTIC)
10.What is the climax vegetation in the Tundra? SHRUBS & LOW BUSHES
& MOSS
11.What type of climate does the Tundra experience? POLAR (Tundra)
12.Name one adaptation organisms have in the tundra. PLANTS: Shallow
roots are needed because 1-3 meters below the surface the soil is
completely frozen (Permafrost). The fast flowering and reproduction
cycle is needed because the growing season is very short, lasting only
1-2 months. Animals : Hibernation from the cold winter is one
adaptation Migration in for the summer season and out for the winter
season is a common strategy for Birds and even larger animals like
caribou. The development of insulating features like thick fur & fat
insulation is common among polar bears and other mammals. White
fur/feathers to help with camouflage is another common adaptation.
13.What producer forms the base of the ecosystem in the polar ice caps?
PHYTOPLANKTON
14.What climate does the polar ice cap ecosystem receive? POLAR
CLIMATE (ICE ACP)
15. Name one high latitude ecosystem the is located in both hemispheres.
POLAR ICE CAP
Mid Latitude Ecosystems
Temperate Grasslands
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The “climax vegetation” in Temperate Grasslands is grass with:
o shallow roots;
o a small water requirement.
The location of the Temperate grassland can be seen by analyzing the
world ecosystem map (figure 6.8) on page 102. It is found in North
America, South America, Australia and Eurasia.
Grasses are well adapted to lack of water:
o the small size of the plant means that it requires less water.
The climate in the Temperate grassland is semi-arid in most locations
but in some regions it is temperate cold winter. Look at figure 6.8 on
page 102 and locate the Temperate grassland; then turn to page 75
and locate the semiarid climate region. The two match very closely.
Temperate Deciduous Forests
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The “climax vegetation” in Temperate forests is deciduous trees like
oak, birch and maple which:
o lose leaves in summer
The location of the Temperate Forests can be seen by analyzing the
world ecosystem map (figure 6.8) on page 102. It is found
predominantly in North America and South America but is present in
Australia and Europe and Asia.
Deciduous trees are well adapted to lack of water in winter.
o losing their leaves in winter helps them reduce water loss. Most
water loss occurs through the leaves.
The climate in the Temperate Forest is temperate mild winter. Look at
figure 6.8 on page 102 and locate the Temperate forests; then turn to
page 75 and locate the temperate mild winter climate region. The two
match very closely.
Assigned Readings
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"Climate and ecosystems" on pages 103-107 of your text book.
Assigned Activities
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Complete question #22 on page 104 of your text book.
Test yourself
1.
2.
3.
4.
5.
What is the climax vegetation in the Temperate grasslands?
What is the climax vegetation in the temperate forests?
What is the climate in the temperate grasslands?
What is the climate ion the temperate forests?
Why are deciduous trees well adapted to the climate of temperate mild
winters?
6. Which two continents do NOT contain temperate forests and temperate
grasslands.
7. Which continents contain most of the temperate forests?
Answers
1. What is the climax vegetation in the Temperate grasslands? GRASSES
2. What is the climax vegetation in the temperate forests? DECIDUOUS
TREES
3. What is the climate in the temperate grasslands? SEMI_ARID
4. What is the climate in the temperate forests? TEMPERATE MILD
WINTER
5. Why are deciduous trees well adapted to the climate of temperate mild
winters? LOOSING THEIR LEAVES IN WINTER HELPS PREVENT WATER
LOSS
6. Which two continents do NOT contain temperate forests and temperate
grasslands. AFRICA & ANTARCTICA
7. Which continents contain most of the temperate forests? NORTH
AMERICA & ASIA & EUROPE
Low Latitude Ecosystems
Tropical Rain Forests
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The climax vegetation in The Tropical Rain Forest is Tall Evergreen
Broadleaf Trees with:
o Butress roots.
The location of the Tropical Rainforest can be seen by analyzing the
world ecosystem map (figure 6.8) on page 102. It is found in South
America, Africa, Australia and South east Asia. and is contained with in
the tropics.
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The tall trees are well adapted to the thin soil with buttress roots
(figure 6.15 on page 108) to help support their height. Some plants
are epiphytes which are well adapted to the rain forest. They reach the
sun by lying in the canopy while they get water through roots that
hang in the air and absorb moisture. Some animals are adapted to
spend their entire life in the canopy.
The climate in the Tropical rain forest is Tropical wet in most locations
but in some regions it is tropical wet and dry. Look at figure 6.8 on
page 102 and locate the Tropical rain forest; then turn to page 75 and
locate the tropical wet climate region. The two match very closely.
Savanna Grasslands
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The climax vegetation in the savanna is grass with:
o shallow roots;
o small water requirement.
The location of the Savanna can be seen by analyzing the world
ecosystem map (figure 6.8) on page 102. It is found in South America,
Australia, Africa and Southeast Asia.
Grasses are well adapted to lack of water:
o the small size of the plant means that it requires less water.
The climate in the Savanna is tropical wet & dry in most locations but
in some regions it is semi-arid . Look at figure 6.8 on page 102 and
locate the Savannas; then turn to page 75 and locate the Tropical Wet
and dry climate region. The two match very closely.
Deserts
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The climax vegetation in the Desert is cacti and fleshy plants with:
o long roots;
o water storage capability;
o leaves modified as needles.
The location of the Desert can be seen by analyzing the world
ecosystem map (figure 6.8) on page 102. It is found in North America,
South America, Australia, Africa and Asia. Deserts are mostly
concentrated in two bands around the earth 10-30 North and South of
the equator.
Cacti are well adapted to lack of water. They are often referred to as
Xerophytes:
o long roots help them obtain water deep in the water table;
o water storage capability gives them the ability to endure long
periods without rain;
o leaves modified as needles reduces the surface area for
transpiration and helps reduce grazing which would severely
increase water loss.
Many animals have unique adaptations to the desert:
deer mice can get all the water they need from the food they
eat;
o toads have the behavioural adaptation of hibernating thorough
the driest seasons;
o some Reptiles reduce water loss by excreting solid uric acid
crystals instead of water containing urine;
o some mammals have the behavioural adaptation of nocturnal
behaviour, which keeps them out of the day time heat.
The climate in the Desert is Arid. Look at figure 6.8 on page 102 and
locate the Deserts; then turn to page 75 and locate the arid climate
region. The two match very closely.
o
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Mountain Ecosystems
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Mountains ecosystems are not exclusively low latitude, on the contrary
they occur in most latitudes and as you will see in figure 6.10 on page
104 mountains can contain all types of ecosystems from all latitudes.
Figure 6.10 on page 104 well-illustrates the fact that latitudinal
succession closely parallels altitudinal succession.
The changes we see in ecosystems as we move north from the equator
are generally, tropical rain forest, Temperate forest, Coniferous forest,
shrubby tundra and then polar ice cap. The same changes in
ecosystem can be seen as you move up a tropical mountain.
Mountain ecosystems are not very unique—they vary with altitude and
temperature.
Assigned Readings
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"Adaptation in Ecosystems" on pages 108-109.
Test yourself
1.
2.
3.
4.
5.
6.
7.
What is the climax vegetation in the tropical rain forest?
What is the climax vegetation in the desert?
What is the climax vegetation ion the savanna?
What climate is experienced in the desert?
What climate is experienced in the tropical rain forest?
What climate is experienced in the savanna?
Cacti are adapted to the desert climate because their leaves are
adapted as _?_.
8. The tall trees of the tropical rain forest are able to support themselves
in the thin soil with _?_.
9. Some mammals in the desert are able to reduce their exposure to the
sun and heat with what kind of behavior?
10.Some reptiles reduce their water loss during excretion by excreting
_?_.
11.Which continent has the largest percentage of savanna?
12.Between what latitudes would you expect to find desert ecosystems?
13.Between which latitudes would you expect to find tropical rain forests?
14.How unique are mountain ecosystems?
15.What are xerophytes?
16.What are epiphytes?
Answers
1. What is the climax vegetation in the tropical rain forest? EVERGREEN
BROAD LEAF TREES
2. What is the climax vegetation in the desert? CACTI AND OTHER
FLESHY PLANTS
3. What is the climax vegetation ion the savanna? GRASSES
4. What climate is experienced in the desert? ARID
5. What climate is experienced in the tropical rain forest? Tropical Wet
6. What climate is experienced in the savanna? TROPICAL WET AND DRY
- SEMIARID
7. Cacti are adapted to the desert climate because their leaves are
adapted as _?_. THORNS/NEEDLES
8. The tall trees of the tropical rain forest are able to support themselves
in the thin soil with _?_. BUTTRESS ROOTS
9. Some mammals in the desert are able to reduce their exposure to the
sun and heat with what kind of behaviour? NOCTURNAL
10.Some reptiles reduce their water loss during excretion by excreting
_?_. URIC ACID CRYSTALS
11.Which continent has the largest percentage of savanna? AFRICA
12.Between what latitudes would you expect to find desert ecosystems?
10-30N and 10-30 S
13.Between which latitudes would you expect to find tropical rain forests?
TROPIC OF CANCER AND TROPIC OF CAPRICORN
14.How unique are mountain ecosystems? NOT UNIQUE HEY VARY WITH
ALTITUDE BUT ARE LIKE THE ECOSYSTEMS OF LATITUDINAL
SUCCESSION.
15.What are xerophytes? PLANTS ADAPTED TO DRY CLIMATES
16.What are epiphytes? PLANTS THAT LIVE ON OTHER PLATS AND HANG
FROM THEIR BRANCHES
World Ecosystems Lab
This lab will give you some practice in predicting the type of ecosystem:
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that exists in a specific type of climate;
from the climax vegetation;
from a climate graph.
Assigned Activities

Click on "World Ecosystems Lab" open it, print it and complete it. You
will need coloured pencil leads for this lab.
World Soils
Soil Types
Soil Characteristics
There are several characteristics of soil that affect its value for farming and
growing vegetation.
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Organic Content: a soil's fertility is determined as a ratio of the
organic content to the content of ground bed rock.
Mineral content: varies with precipitation because heavy rains tend
to leech soils removing minerals from the root region of soil.
Soil Texture: this will be discussed in the next lesson but refers to
the mixture of fine particles (sand), very fine particles (silt) and extra
fine particles (clay). The best texture for agriculture is an even
mixture of each.
Soil Profile
To understand about different soils you must understand that there are fairly
distinct layers within soil.
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Top Layer: Dark color & Rich in Humus
2nd Layer: Mineral layer deposited from above
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3rd Layer: weathered bed rock
4th Layer: Bed rock
As you can imagine the thickness and quality of the top humus layer is very
important for plant life.
Three Types of Soil
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Podzol: soils which predominate the boreal forest and tend to be
somewhat acidic
Chernozem: soils which tend to be the best for agriculture. They are
found in grasslands which are semi-arid resulting in less leeching and
a mineral rich soil.
Latosol: soils which are very infertile due to the high amount of
leeching. They are found in tropical rain forests with high amounts of
rain which result in leeched mineral-poor soil.
Environmental Factors Affecting Soil
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Temperature: affects the development of humus. Too cold and the
decay of organic matter is slowed considerably.
Precipitation: affects the mineral content of soil. Too much rain and
minerals are leeched beyond the reach of plant roots. Too much rain
also results in eluviation which moves small particles down through the
soil.
Assigned Readings
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
"Earth's Soil Resource" on page 135;
"Types of soil" on pages 136-138.
Assigned Activities

Questions 13-16 p. 136-137
Soil Texture
Soil texture refers to the size of particles in the soil. While you don't have to
memorize the exact sizes given on p.138 you should realize that:
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stones are approximately baseball-sized;
gravel is small stones;
sand is fine particles;
silt is very fine particles;
clay is extremely fine particles.
Soil is predominantly composed of sand, silt and clay. Its texture is
determined by the mixture of these three. The best agricultural soils are an
even mixture of all three and are referred to as Loam.
You must be familiar with the soil texture triangle on p.139 and the question
in the "activities" section takes you through the use of the triangle.
Assigned Readings

"Soil Texture" p.138-139.
Assigned Activities

Complete questions #17-22
Threats to Soil
While the earth's surface is covered in soil the amount of fertile soil valuable
for agriculture is limited and is dwindling yearly. Poor soil management can
lead to loss of fertile soil.
Grasslands are semi-arid regions with extremely fertile soil. However, if
proper soil management is not practiced these are among the most fragile
places. Globally desertification of grasslands adjacent to deserts has been a
problem.
Agricultural land on slopes/hills or mountains are very susceptible to water
erosion.
Urban expansion has also been a factor in the loss of agricultural land.
People have traditionally settled in rich farmland and increasing urbanization
is covering up good farmland.
Overgrazing, flooding and deforestation have also lead to the degradation of
arable land.
Assigned Readings



Desertification p. 121-122
Case Study "Desertification in The Sahel" p. 123-124
"Threats to Soil" on page 140-143 of your text.
Assigned Activities

Complete question #23-25 on page 140-143 of your text book.