▲
Bras d’Or Lake is an
estuary with a variety
of habitats, including
salt marshes, sheltered
bays, and deep-water
basins. As a result, the
diversity of species
supported by Bras d’Or
Lake is high. In 2011,
Bras d’Or Lake was
designated as a United
Nations Educational,
Scientific and Cultural
Organization (UNESCO)
Biosphere Reserve.
Agencies and organizations
at the national, provincial,
and local levels, including
First Nations groups,
citizens, and scientists
developed a management
plan for the area based on
sustainability—the idea
that ecosystems and the
organisms they support,
including humans, will be
able to function optimally and
endure for future generations.
As you read Unit 4, you will
learn more about the importance
of sustainable ecosystems and
how people’s attitudes toward
sustainability are shifting. You
will also read more about how
the Bras d’Or Lake Biosphere
Reserve designation, and other
examples like it, result from the
actions of individuals, as well
as local, provincial, national,
and international groups and
governments working together to
increase the sustainability of Earth’s
ecosystems.
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Unit Contents
7
Factors that Affect
Sustainability
7.1 Components of Sustainable
Ecosystems
7.2 Populations and Sustainability
7.3 How Human Activities Can Affect
Sustainability
8
Shifting Perspectives on
Ecosystems
8.1 How Our Understanding of
Ecosystems Has Changed
8.2 The Shift Is On—Attitude, Actions,
and Empowerment
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What You Should Recall About…Interactions Within Ecosystems
•
•
•
•
A population is a group of organisms of the
same species living in the same area at the
same time.
A community is composed of all of the
populations that live and interact with each
other in a particular area.
An ecosystem is a community of organisms
interacting with each other and with nonliving factors in their environment.
Ecosystems can be large, such as forests,
croplands, rivers, lakes, and oceans. Ecosystems
can also be small, such as a rotting log or a
puddle of water. Ecosystems may be terrestrial
(located on land) or aquatic (located in water).
Check What You Recall
1. Define the term ecosystem.
2. Give an example of two large ecosystems and
two small ecosystems.
3. Which of the following are examples of
abiotic factors in an ecosystem?
(a) temperature, light, and oxygen
(b) plants, animals, and micro-organisms
(c) water, soil, and nutrients
(d) moisture, space, and salinity
(e) a, c, and d
•
•
Every ecosystem has biotic and abiotic
components. The biotic factors in an
ecosystem include plants, animals, and
micro-organisms. Abiotic factors refer to nonliving things such as water, oxygen, light,
temperature, nutrients, soil, and salinity (the
amount of salt in an environment).
An ecosystem can be healthy or unhealthy,
depending on the interrelationships among its
components.
4. Examine the forest ecosystem shown below.
Make a table with the headings “Biotic” and
“Abiotic” as shown below. Give your table a
title. Under each heading in your table, list
the components of the forest ecosystem in
the appropriate category.
Biotic
Abiotic
A Forest Food Chain
A Forest Ecosystem
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What You Should Recall About…Flow of Energy Within Ecosystems
•
•
•
•
•
•
•
•
Interactions within ecosystems and among
ecosystems provide a constant flow of energy
for the organisms that inhabit the ecosystems.
All organisms on Earth rely on energy from
the Sun.
Photosynthesis is a process in the cells of plants,
algae, and some bacteria that converts light
energy from the Sun into chemical energy.
Cellular respiration is a process in the cells of
organisms that converts the energy stored in
chemical compounds into usable energy.
A producer is any organism that gets the
energy it needs by making its own food.
A consumer is any organism that gets the
energy it needs by eating producers or other
consumers.
Producers transfer energy to consumers
through food chains and food webs.
A decomposer is an organism that obtains
energy by consuming dead plant and animal
matter.
Check What You Recall
5. Complete each of the following sentences,
using one of the organisms from the forest
ecosystem shown the previous page.
(a) A ■■■ is a decomposer because…
(b) A ■■■■ is a producer because….
(c) A ■■■■ is a consumer because….
6. The food chain shown in the illustration
on the previous page is just one of many
food chains in a forest ecosystem. Using the
organisms shown in the forest ecosystem,
draw a different food chain.
7. Which of the following organisms are
examples of consumers?
(a) dandelions
(b) mushrooms
(c) fungi
(d) all of the above
(e) none of the above
•
A tropic pyramid is a model that shows the
transfer of energy from one level of organism
to the next within a food chain. An example
of a tropic pyramid is shown below.
great horned owl
1 energy unit
long-tailed weasel
10 energy units
jackrabbit
100 energy units
grass
1000 energy units
Tropic pyramid
This tropic pyramid shows that a large number of producers are
required to provide the energy (food) needed for a much smaller
number of consumers.
8. Which of the following organisms are
examples of producers?
(a) cats
(d) grasses
(b) dogs
(e) spiders
(c) cows
9. Examine the aquatic food chain shown below.
Identify whether each organism is a producer
or a consumer.
floating algae
mosquito larva
minnows
perch
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10. Identify four food chains in the food web
shown here.
producers
oxygen
habitat
great
horned
owl
bat
weasel
shrew
mouse
snowshoe hare
grouse
insects
12. Use the words below to write a brief
explanation of why trees are important to
forest ecosystems.
green plants
11. Refer to the diagram of the tropic pyramid on
the previous page. Draw a tropic pyramid of
your own that features different organisms.
food
leaves
decompose
shade
plants
photosynthesis
13. Choose one of the following events. Make a
flowchart to show how the event might affect
a forest ecosystem.
(a) A forest fire rages through the forest.
(b) A logging company clear-cuts the trees in
the forest.
(c) A beaver builds a dam in a nearby pond
that results in the stream drying up.
(d) Hunters kill all of the wolves in the area.
(e) A species of beetle kills all of the pine
trees in the area.
What You Should Recall About…Cycling of Materials Within Ecosystems
•
•
•
•
•
•
276
Abiotic and biotic interactions cycle matter in
terrestrial and aquatic ecosystems.
A nutrient is any substance that an organism
needs to sustain its life.
All producers and consumers use nutrients
to grow and to carry out their life functions.
When organisms die, decomposers return the
nutrients to the environment.
The pattern of continual use and re-use of
the nutrients that living things need is called a
nutrient cycle.
Photosynthesis and cellular respiration play
a key role in the transfer of energy and the
cycling of matter through ecosystems.
Photosynthesis uses carbon dioxide and
water, and produces glucose and oxygen.
Cellular respiration uses glucose and oxygen,
and produces carbon dioxide and water.
Photosynthesis and cellular respiration cycle
carbon and oxygen in ecosystems.
A General Nutrient Cycle
producers
heat
consumers
decomposers
non-living
nutrient substances
(particles of matter)
heat
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18. Refer to the diagram titled “A General
Nutrient Cycle.” How does this diagram
show that a constant flow of energy and
matter is needed for living things?
19. What substances are released by all
organisms—including plants and animals—
during cellular respiration?
20. Draw a labelled cycle chart to show how
photosynthesis and cellular respiration cycle
matter in ecosystems.
Check What You Recall
15. Use drawings, words, or a graphic organizer
to explain the following terms: nutrient,
nutrient cycle.
16. The living things that decompose dead
organisms link the biotic and abiotic parts of
ecosystems. How do they do this?
17. What substances do plants require to carry
out photosynthesis?
What You Should Recall About…Natural Changes in Ecosystems
•
•
•
Ecosystems are dynamic (constantly changing)
due to a variety of factors.
Succession, shown below, is the series of
natural changes in an ecosystem that occurs
over time, following a disturbance such
as a forest fire, flood, windstorm, or the
construction of a beaver dam.
Primary succession takes place in areas lacking
soil.
0
Annual
plants
1–2 years
Shrubs
Grasses/
herbs
3–4 years
4–15 years
•
•
•
Secondary succession occurs in areas that were
previously inhabited.
Each of the stages of succession is ideal for
different species.
A climax community is a stable, mature
community that results when there is
little change in the species inhabiting the
community.
Pines
Young oak/
hickory
Pines die,
oak/hickory
mature
5–15 years
10–30 years
50–75 years
Mature
oak/hickory
forest
Succession is a series of changes that leads to a mature community.
Check What You Recall
22. Explain succession in your own words.
23. “Succession may be slow and difficult to
observe over short periods of time, or it may
be rapid.” Explain why you agree or disagree
with this statement.
24. A beaver pond changes an area from a forest
to a flooded forest, then to a sunny pond
and, finally, to an abandoned pond that
becomes a beaver meadow. For which species
might a beaver meadow be ideal?
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7 000 000 000
I
magine the entire history of the universe compressed into a single year. Such a “cosmic
calendar” was first conceived by astronomer Carl Sagan. In such a year, Earth was
not formed until early September. Life flourished, but it was not until the beginning of
December that plants created our current oxygen-rich atmosphere through photosynthetic
activity. By December 19, ancient fish dominated the oceans, while December 24
brought with it dinosaurs. From the tiny to the enormous, dinosaurs lived for a mere
five days before becoming extinct on December 29. Where do Homo sapiens fit into
this year? At 11:59 pm on December 31, primitive human beings were establishing
themselves in hunter-gatherer societies across the globe. The development of the rest of
human civilization took place in this final minute. It was only during the final seconds of
that minute that our own modern society came into being, spurred by the start of the
Industrial Revolution in the 1700s. Yet within that time, a few heartbeats in the span of
that year, we transformed a small population into the mega-population of our modern age,
7 000 000 000 people as of November 2011. As our population changed so did the world
we live in, as we significantly altered many of the life-support systems our planet relies on.
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LAUNCH ACTIVITY 7
Visualizing Seven Billion
Most people find it difficult to visualize extremely large
numbers. While people may talk about Earth being
home to over seven billion people, they often have little
concept of how many people actually make up this
What
Willyoulearn
number. InYou
this activity,
will design and build a model
that compares different numbers and measurements of
In
this chapter
will: a sense of how large seven
familiar
objects you
to provide
billion
really
is.
• Describe natural and constructed fluid
systems.
What to Do
• Explain how compression of fluids can be
1. In a group, brainstorm a list of familiar objects that
used to cause movement.
could be compared in terms of number and another
• Identify and solve problems in natural
measurement to help people visualize seven billion.
and
fluid
Yourconstructed
comparisons
maysystems.
involve measurements such
as volume, mass, time, area, length, etc. For example,
a penny is 19 mm in diameter. The circumference of
Earth at the equator is 40 075.16 km. How many
pennies would it take to cover 40 075.16 km?
___________
40
075.16 km
19 mm
___________
075.16 km
= 40
0.000 019 km
= 2 109 218 947 pennies
Approximately 2 billion pennies laid flat and lined up
end-to-end would circle Earth at the equator. Thus,
seven billion pennies would circle Earth about
3.5 times!
2. Prepare an outline of your model. In your outline:
• provide a description of how your model
works, including the objects and measurements
compared in your model.
• include a list of materials and equipment needed
to create your model.
• explain whether you must carry out research to
complete your model.
3. Have your teacher to approve your outline.
4. Build your model and demonstrate to the other
groups in your class how it enables the number 7
billion to be visualized.
What Did You Find Out?
1. Why do you think it is difficult for people to visualize
very large numbers?
2. How effectively do you think your model enables
people to visualize seven billion? Explain.
3. How might you improve your model if you were to
redesign it?
What You Will Learn
Why It Is Important
In this chapter, you will
• describe a sustainable ecosystem
• distinguish between biotic and abiotic factors, and explain
how biotic and abiotic factors can affect the sustainability of
an ecosystem
• explain, referring to biotic and abiotic factors, why different
geographical locations can sustain similar ecosystems
• identify and explain how humans can affect the
sustainability of ecosystems
• describe and explain the impact of bioaccumulation on the
diversity of consumers at different trophic levels
Ecosystems consist of a variety of components,
including, in many cases, humans. The sustainability
of ecosystems depends on balanced interactions
between their components. Human activity can
affect the sustainability of aquatic and terrestrial
ecosystems.
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7.1 Components of Sustainable
Ecosystems
What Do You Think?
• What does the term “sustainable” mean to you?
• What do you think are the characteristics of a sustainable ecosystem?
• What does it mean to describe an ecosystem as unsustainable—for example,
unsustainable for whom?
Key Terms
ecosystem
sustainable ecosystem
ecosystem all the
interacting parts of a
biological community and
its environment
Take a moment to think about what the term ecosystem means to you.
An ecosystem can be very small or very large, or any size in between. A
rotting log, such as the one shown in Figure 7.1A, is an ecosystem. So is
a pond (B), an urban park (C), a forest, a desert, an ocean, a spruce tree,
a human body, and even Earth as a whole. An ecosystem includes all the
interacting parts of a biological community and its environment. The prefix
eco- is from the ancient Greek word for home. This is a fitting prefix, since
ecosystems are the natural homes of the many organisms that live in them.
A
B
C
Figure7.1 Ecosystems exist in many
shapes, sizes, and locations.
Describe Choose an ecosystem you
see every day and describe it. What
living and non-living things make up
the ecosystem?
Sustainable Ecosystems
sustainable ecosystem an
ecosystem that is capable of
withstanding pressure and
giving support to a variety
of organisms
Now think about what the term sustainable means to you. Other words
such as support or phrases such as something that lasts a long time may
come to mind. Why do think it might be important for ecosystems
to be sustainable? What things, or services, do living things get from
ecosystems? Even though you may not think about it, you and other
living things get oxygen, water, food, and shelter from ecosystems every
day. These are things that you and other living things need to survive.
A sustainable ecosystem is an ecosystem that is capable of withstanding
pressure and giving support to a variety of organisms. When the term
sustainable ecosystem is used, the word sustain has two meanings: “to
support” and “to endure.”
The Need for Sustainable Ecosystems
To endure means to continue in the same state. Sustainable ecosystems
endure, but they also support a wide variety of organisms. All organisms
require sustainable ecosystems for survival. In fact, many organisms
depend on more than one sustainable ecosystem to survive.
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For example, ruby-throated hummingbirds, shown in Figure 7.2,
spend the summer in gardens and along the edges of forests of eastern
Canada. In the fall, they fly thousands of kilometres to spend the winter in
the tropical forests of Central America. In the spring, they begin the long
flight back to Canada. Along the way, they stop to drink water, eat nectar
and insects, and rest. Because these birds, and many others, migrate long
distances every year, they are dependent on the many ecosystems for food
and shelter along their migratory route.
Another example of an organism that needs several sustainable
ecosystems in which to survive is the American eel. The American eel was
once one of the most abundant fish in the St. Lawrence River. Today, the
estimated number of American eels in the St. Lawrence and Great Lakes
has decreased by more than 90 percent.
American eels are long, snake-like fish. They are a native species and
have an important role in the Great Lakes ecosystem. Eels eat insects,
crustaceans, fish, frogs, and dead animals. They are prey for other fish,
birds, and mammals. American eels migrate great distances and change
dramatically during their life cycles, as shown in Figure 7.3. Eels spend
most of their lives in fresh water, but return to the sea to lay eggs. Both
saltwater and freshwater species and their ecosystems are affected by a
decrease in the eel population.
Because the eel’s life cycle is so long and covers so much distance, the
species encounters many threats. Many mature eels do not complete their
journey down the St. Lawrence River and back to the Sargasso Sea. About
40 percent of these eels are shredded and killed in dam turbines in the river.
Dams also block young eels migrating upstream toward the Great Lakes.
Overfishing has contributed to the decline of American eels. Ontario
cancelled its eel fishery in 2004, but eel fishing takes place elsewhere.
Overharvesting of seaweed, which makes up the spawning habitat for eels,
could also be contributing to a decrease in eels. Chemical contaminants
may be affecting eel fertility. Governments, industry, and scientists are
working together to decrease the threats that eels face at different points
in their life cycles.
G re
en l
larvae
an d
eggs
St. Lawrence R.
ocean
continent
ATLANTIC
OCEAN
reproduction
Gulf of
Mexico
Sargasso
Sea
mature eels
Figure7.3 American eels hatch in the Sargasso Sea in the Atlantic Ocean. The larvae migrate to the
St. Lawrence River and the Great Lakes. Mature eels often spend 10 to 15 years in the Great Lakes
before returning to the Sargasso Sea to reproduce and die.
summer
winter
migration
Figure7.2 Ruby-throated
hummingbirds fly north from Mexico
and Central America each spring.
Along the way, they need resources
from sustainable ecosystems to
survive. Of the five species of
hummingbird in Canada, the rubythroated hummingbird is the only one
found in Nova Scotia.
Did You Know?
The Mi’kmaq refer to the
American eel as Ka’t and have
always harvested them as an
important food source. The Ka’t
is also used by the Mi’kmaq for
medicinal purposes, in which the
dried skin of the eel is used as
wrap for sprains or worn against
the skin to relieve headaches.
The dried skin is also used as a
binding for clothes or to make
harpoons.
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<
S
l
Biotic and Abiotic Parts of Ecosystems
Every ecosystem has biotic and abiotic parts. Biotic refers to the living
parts of an ecosystem and the interactions among them. The biotic parts
of an ecosystem include plants, animals, and micro-organisms. Abiotic
refers to the non-living parts of an ecosystem. The abiotic parts of an
ecosystem include water, oxygen, light, nutrients, and soil.
Biotic Characteristics of an Ecosystem and Sustainability
Interactions among living things include symbiosis, predation, and
competition, all shown in Table 7.1. All biotic interactions in an
ecosystem have some effect on the ability of that ecosystem to endure and
to support all the organisms that are a part of it. In other words, all biotic
interactions in an ecosystem affect its sustainability.
Table 7.1BioticInteractionsandSustainability
BioticInteraction
HowItWorks
EffectsonSustainability
Symbiosis
Symbiosis is the interaction between
members of two different species that live
together in a close association. For example,
photosynthetic algae live inside the tissues
of tropical reef-building corals. The algae
provide the coral host with up to 90 percent
of the coral’s energy needs. At the same
time, the coral provides the algae with
protection, nutrients, and a constant supply
of carbon dioxide for photosynthesis.
In 1998, about 16 percent of the world’s tropical
coral reefs were destroyed when the corals within
them turned white. This is known as bleaching.
Bleaching occurs because of a breakdown in the
symbiotic relationship between the coral animal and
its photosynthetic algal partner. Although not fully
understood, scientists hypothesize that higher than
normal temperatures cause the coral to lose the algae,
which leads to bleaching. Elevated sea temperatures
that last as little as six weeks can lead to coral death.
Predation
Predation occurs when one organism (the
predator) consumes another organism (its
prey) for food. The sea otter shown in the
photograph is a predator. Its prey includes
sea urchins, clams, crabs, and small fish. The
sea otter is itself prey for other predators,
such as sharks and killer whales. In this way,
organisms are linked together through the
food chain.
Sea otters are important predators in British
Columbia’s coastal kelp forests. Sea otters eat sea
urchins, which feed on kelp. If the sea otter population
declines, as it did in the 20th century, the sea urchin
population increases. As more sea urchins eat kelp, the
kelp biomass decreases. When this happens, the fish
that depend on kelp forests as a habitat also decline in
number. The relationship between predators and their
prey can influence the population of both the predator
and the prey, as well as affect the entire ecosystem in
which they live.
Competition
Competition occurs when two or more
organisms compete for the same resource,
such as food, in the same location at the
same time. Scientists believe that the
bobcat shown in the bottom photograph
may compete for prey with the endangered
population of Canada lynx on Cape Breton
Island. Competing for resources takes
energy. Energy expended on competition
is energy that is taken away from other
important life processes, such as growth
and reproduction.
The population of Canada lynx was designated as
endangered in 2002 under the Nova Scotia Endangered
Species Act. Threats to the population include competition
with the bobcat, as well as competition with and being
preyed on by fishers and coyotes. Scientists think that
bobcats, coyotes, and fishers may be able to out-compete
the Canada lynx in human-altered environments, such
as areas where the number of roads has increased, or
when climate change affects the amount of snow in
winter. Competition can influence the population size and
success of a group of organisms. Sometimes, one group of
organisms is outcompeted by another group.
Canada lynx
Bobcat
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Abiotic Characteristics of an Ecosystem
The abiotic characteristics of an ecosystem, described in Table 7.2, are as
important as the biotic characteristics. In fact, all living things require the
abiotic parts of ecosystems to survive.
Table 7.2AbioticCharacteristicsandSustainability
AbioticCharacteristic
Water
Oxygen
WhyItIsImportant
EffectsonSustainability
All organisms need water to survive.
Plants take up water through
their roots. Some animals need
water to help regulate their body
temperature. Animals also use
water to get rid of wastes. Many
organisms live in freshwater and
saltwater ecosystems.
Both natural processes and
human activities can affect the
amount and quality of water in
an ecosystem. Water sources can
dry out during long, hot periods
with no rain. Chemicals from
industries and agriculture can
contaminate water.
Many organisms, including plants
and animals, need oxygen for their
life processes. Aquatic organisms
get oxygen from water.
Sometimes, as a result of human
activities, oxygen levels in water
can get so low that fish and
other organisms cannot survive.
Light
Nutrients
Plants and other organisms such as
algae need light for photosynthesis,
a life process in which organisms
produce their own food.
All organisms need nutrients to grow.
For example, plants and animals
need nitrogen and phosphorus.
The amount of light that an
ecosystem receives can vary.
Plants near the floor of a forest
may be shaded by taller trees.
Light in an aquatic ecosystem
can be affected by the amount of
sediment in run-off.
Nutrient levels in an ecosystem
can become unbalanced as a
result of human activities.
Soil
Soil provides nutrients for plants and
a habitat for many micro-organisms.
Top layers of soil, which contain
the most nutrients, can be
washed away if there is heavy
rain or if too many trees have
been cut down.
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Different Geographic Locations Can Sustain Similar
Ecosystems
Figure 7.4 shows areas of the world that have temperate deciduous
forests. Not only are they found in Nova Scotia, but also throughout the
eastern United States, western Europe, and eastern Asia. Although it may
seem as though these countries and continents would not have much in
common, in some areas within their borders, they all have similar abiotic
and biotic characteristics that support temperate deciduous forests.
Figure7.4 Areas that contain
temperate deciduous forests are
shaded in green.
Describe Before reading ahead,
describe the characteristics of a
temperate deciduous forest based
on your prior knowledge and
experiences.
Temperate Deciduous Forests
Temperate deciduous forests are defined by a particular set of abiotic and
biotic features. The abiotic features of temperate deciduous forests include
receiving between 75 cm to 180 cm of precipitation per year, equally
distributed throughout the year. Seasonal changes between summer and
winter are very large. Temperatures range from 30ºC in winter to 30ºC
in summer. Temperate deciduous forests are found in areas of the world
that have four distinct seasons and a long, warm growing season. Fallen
leaves that break down and release nutrients enrich the soil in temperate
deciduous forests.
The main biotic feature of temperate deciduous forests is trees that
lose their leaves during the winter. The forest has a complex structure
that consists of plants that grow in four to five layers. Tall maple, oak,
and birch trees grow in the canopy, or top layer, shown in Figure 7.5A.
The interaction between the abiotic factor of light and the biotic factor
of different sizes and heights of plants influences the biodiversity of the
ecosystem. As light penetrates the layers of the forest, the result is an
understorey that has great biodiversity. As shown in Figure 7.5B, shorter
trees occupy the second layer, with shrubs in the third layer. Berries are
found in the fourth layer, and ferns, club mosses, wildflowers, and mosses
on the forest floor, shown in Figure 7.5C. Deciduous trees shed their
leaves in winter, which prevents water loss and reduces breakage of limbs
from heavy snow. Thick bark limits moisture loss from the trees.
The many layers in the forest provide a variety of habitats for squirrels,
rabbits, skunks, cougars, deer, wolves, bears, and amphibians. Squirrels,
chipmunks, and blue jays store nuts and seeds in tree hollows. Some
mammals hibernate. Many birds migrate to warmer areas in winter.
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A
B
C
Threats to Sustainability
There are several factors that threaten the sustainability of temperate
deciduous forest ecosystems worldwide, including acid precipitation and
clearcutting the forests. Temperate deciduous forests in Nova Scotia, in
particular, are very vulnerable to acid precipitation because the chemistry
of the soil has little ability to buffer the acid. Acid precipitation can
weaken trees’ ability to resist pests, disease, and frost. It also causes them
to produce fewer seeds. In clearcutting, the land may be cleared to use
for agriculture, the timber used to make wood products. In many areas of
the world, clearcutting of forests leads to loss of habitat for animals and
other organisms that grow in temperate deciduous forests.
7-1A Similar Ecosystems Around the
World
Just as there are temperate deciduous forests in eastern
Canada and eastern Asia that have similar abiotic
and biotic features, there are many other examples of
ecosystems that are geographically separated but also
have similar characteristics. In this activity, you will learn
more about these ecosystems.
What to Do
1. Your teacher will assign your group to research one
of the following ecosystems:
• tundra
• intertidal zone
• boreal forest
• coral reef
• temperate grasslands
• estuaries
• tropical rainforest
• open ocean
• hot desert
Figure7.5 (A) The canopy is the top
layer of any forest.(B) Shorter trees
and shrubs grow in the understorey
of a temperate deciduous forest. (C)
Mosses, ferns, and wildflowers grow
on the forest floor.
T hi nk Abo u t It
2. Research more information about the ecosystem
your group is assigned. Be sure your research
answers the following questions:
• Where in the world can this ecosystem be found?
• What are the main abiotic features of the
ecosystem?
• What are the main biotic features of the
ecosystem?
• What are the threats to sustainability?
• How can the ecosystem be preserved or the
sustainability be increased?
What Did You Find Out?
1. Choose a format to present the results of your
research.
2. Share your presentation with the class.
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Dust on the Move
Dust from the Sahara Desert in Africa moves west over the Atlantic
Ocean.
You may think the ground under your feet does not go
anywhere, but soil and dust are constantly on the move,
reshuffling particles around the biosphere. Fine particles
of arid soil from the Sahara Desert are carried by winds
across the Atlantic Ocean and reach North and South
America within days. The soil, an abiotic factor, has an
impact on the biotic factors in ecosystems in other areas
of the world. While scientists have long known that soil
can be transported vast distances, only recently have they
begun to understand the full environmental impact of this
movement.
Scientists estimate that the quantity of soil that
moves large distances in Earth’s atmosphere is
approximately 3 billion tonnes annually. Plants in the
Amazon rainforest have evolved in ways that take
advantage of particles rich in iron, phosphorus, and
organic matter that are carried in the wind from the
African Sahara desert. In the South Atlantic Ocean and
the Caribbean Sea, seaweed and algae flourish after dust
storms.
286
It is believed that climate change is increasing the
intensity of dust storms. Scientists are now hypothesizing
that the increased amount of Saharan dust is also causing
environmental distress. Some dust particles in clouds can
stop rain droplets from falling, reducing precipitation in
some areas.
Of great concern is the devastation caused by the
microbial hitchhikers (micro-organisms) in windborne
soil. Concentrations of bacteria carried across the globe
have been calculated to be from 106 to 109 bacteria
per gram of soil. It is estimated that 30 percent of these
dust micro-organisms can cause disease. Also along for
the ride in soil are viruses and spores from fungi that
are affecting many animal species. Evidence shows that
the death of Caribbean staghorn corals and sea urchins
is directly related to African dust deposits. The fungus
Aspergillus, which is carried in the windborne soil, has
also caused the death of coral sea fans. Disease caused
by fungi has been found to affect Caribbean sugar
cane and banana crops after dust storms. While African
dust in the atmosphere is not new, huge amounts of
dust blowing off Asia is a recent occurrence. Increased
desertification (the creation of deserts) due to less
precipitation and increased land use in Asia is also
producing millions of tonnes of windborne dust. Although
Hawaiian Island plants may gain nutrients from the dust
of Asian deserts, the full extent of the negative effects of
this increased soil movement has yet to be determined.
Questions
1. Explain how the Amazon rainforest ecosystem has
benefited from the Sahara Desert ecosystem.
2. Explain how the increased amount of Saharan
dust moving through the atmosphere has affected
the sustainability of ecosystems, such as those in
the Caribbean.
3. Predict how microbial hitchhikers could affect the
sustainability of ecosystems in Hawaii. Explain
your reasoning.
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Checking Concepts
1. Give examples of two large ecosystems and
two small ecosystems.
2. What is a sustainable ecosystem?
3. What is the two-part meaning of the word
sustain?
4. Use the map in Figure 7.2 to explain how
ruby-throated hummingbirds are dependent
on more than one ecosystem.
5. Why is the American eel an important part of
the ecosystems of the St. Lawrence River and
the Great Lakes?
6. What is symbiosis?
7. Explain the difference between predation
and competition. How can each affect the
sustainability of an ecosystem?
8. List some biotic parts of the ecosystem in
which you live.
9. Identify and describe three abiotic
characteristics of ecosystems. Give an example
of how each characteristic could be affected
by a human activity.
10. Describe the abiotic and biotic characteristics
of temperate deciduous forests.
11. What are two threats to the sustainability of
temperate deciduous forests?
16. Create a poster for a campaign to raise public
awareness about the American eel. Your
poster should highlight the importance of the
eel to the health of the Great Lakes ecosystem
and some of the threats to the sustainability
of the ecosystems in which it lives.
17. Identify each of the following as an example
of symbiosis, competition, or predation.
(a) A western red cedar seedling and a
Sitka spruce seedling are both growing
in a temperate rainforest. Both require
sunlight, nutrients, and water from the
environment.
(b) The common garter snake feeds on mice,
frogs, salamanders, and fish.
(c) Some flowers are pollinated by bats. Bats
receive nectar from the flowers.
18. Use the diagram below to describe two ways
biotic parts and two ways abiotic parts of an
ecosystem interact.
Understanding Key Ideas
12. Use a spider map to identify all of the things
you get from ecosystems that you need to
survive. Then add things you use throughout
the day that are not needed for survival
but still have been derived from ecosystems
somewhere in the world, such as wood
products or energy for transportation. Do
you think that your use and other human’s
use of these things affects the sustainability of
the ecosystems from which they were derived?
Why or why not?
13. Why is it important for all ecosystems on
Earth to remain sustainable?
14. Make an analogy that explains how an
ecosystem is similar to the Internet.
15. Infer why the top layer of soil, an important
abiotic factor in an ecosystem, can be washed
away if too many trees have been cut down.
19. Natural Resources Canada has tips on how
to conserve water, including using low-flow
showerheads, fixing leaking faucets, and
having a landscape that does not require
watering. Why do you think it is important
for Canadians, as well as citizens of other
countries, to conserve water?
Project Prep
How can learning more about biotic and abiotic
factors help you understand how the life
cycle of a product might affect a sustainable
ecosystem?
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7.2 Populations and Sustainability
What Do You Think?
• Why are limiting factors important to the sustainability of ecosystems? • What are some impacts of a population exceeding its carrying capacity? • Why is it important for humans to practice sustainable use? Key Terms
population
exponential growth
limiting factor
carrying capacity
ecological niche
sustainable use
unsustainable
sustainability
population all the
individuals of a species
that occupy a particular
geographic area at a specific
time
exponential growth
accelerating growth that
produces a J-shaped curve
when the population is
graphed against time
A population is a group of organisms of one species that lives in the same
place, at the same time, and can successfully reproduce. All populations
tend to increase when individuals reproduce at rates that are greater
than what is needed to replace individuals that have left the area or died.
This is even true for organisms that reproduce slowly, such as elephants.
Elephants only produce about six offspring in a 100-year life span. In
theory, the descendants of a single pair of elephants could number
19 million after 750 years!
Exponential Growth
Population growth that occurs like this is called exponential growth.
Usually, exponential growth of a population in nature only occurs under
certain conditions and for a short time. In some cases, it is seen when
an organism comes to a new habitat that has a lot of resources, such
as the first time that algae grows in a newly formed pond. In other
cases, it occurs when other pressures on a population are removed. In
South Africa’s Kruger National Park, elephants became protected after
many years of being hunted for the ivory from their tusks. The graph in
Figure 7.6 shows that population numbers were low until about 1960,
when the elephants became protected. After 1960, the population grew
exponentially. Although the elephant population has recovered, it is not
without cost to other parts of the ecosystem. For example, because of
their large size and mass, elephants can damage plants and habitats of
other organisms as they search for their own food.
Figure 7.6 As shown in the graph, after being protected from hunting, the population of elephants in Kruger National Park grew exponentially. Elephant Population
Population Growth of Elephants
in South Africa’s Kruger National Park
288 8000
7000
6000
5000
4000
3000
2000
1000
0
1900
exponential
growth
protected
1920
1940
Year
1960
1980
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Limiting Factors and Exponential Growth
Given the elephant example, you may have already started wondering how
the exponential growth of a population can be sustained. The answer is
that exponential growth cannot be sustained in nature. A female yellow
perch, shown in Figure 7.7, can produce about 23 000 eggs per year.
Even though female yellow perch do not breed until their fourth year, that
one female and her daughters, if they all lived, would produce almost
1 trillion offspring in just five years!
That kind of growth cannot continue for long because no ecosystem
has an unlimited supply of the things that organisms need. These
restrictions are known as limiting factors. As a population increases in
size, each individual has access to fewer resources, limiting the growth
of the population. The young perch, for example, require food for the
nutrients and energy they need to survive, grow, and reproduce. Abiotic
factors require the perch to live in parts of lakes and rivers that are the
proper temperature and pH for growth and activity. The habitat must
have enough dissolved oxygen, light, and hiding places, as well. In natural
ecosystems, there are simply not enough places where 1 trillion or more
yellow perch can have these needs satisfied. Additional biotic factors, such
as symbiosis, predation, and competition, can also regulate population
growth. There are two categories of limiting factors: density-independent
factors and density-dependent factors.
limiting factor a factor
that limits the growth,
distribution, or amount
of a population in an
ecosystem
Figure7.7 If there were no factors
limiting the exponential growth of
yellow perch, a single female and her
daughters could reach almost
1 trillion individuals in five years.
Density-independent factors A density-independent factor is any factor
in the environment that does not depend on the number of members in
a population per unit area. These factors are usually abiotic and include
natural phenomena, such as weather events—extreme storms, droughts,
floods, fires, cold snaps, and heat waves. Pollution of air, land, and water
as a result of human activities can also limit populations. Pollution reduces
the available resources by making some of them toxic.
Density-dependent factors A density-dependent factor is any factor in
the environment that depends on the number of members in a population
per unit area. These factors are usually biotic factors such as disease,
parasites, predation, and competition. For example, outbreaks of disease
tend to occur when population size has increased and population numbers
are high. When population numbers are high, disease is transmitted
easily from one individual to another and spreads quickly throughout a
population because contact between individuals occurs more often. This is
true for human populations as it is for populations of protists, plants, and
other animal species.
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Check Your Understanding
1. When do populations tend to increase?
2. Look again at Figure 7.6. Do you think the elephant populations
in Kruger Park can continue growing exponentially? Explain your
reasoning.
3. List three examples of limiting factors.
4. Occasionally, humans are put in situations in which their resources
are limited. In the summer of 2003, eastern North America
experienced a sustained power outtage lasting several days. What
resources do you think quickly became limited?
Carrying Capacity
Figure7.8 Limiting factors for
Southern Flying Squirrel include
habitat degradation and loss, as well
as competition for food.
Figure7.9 Compare this graph
of fur seal population growth
with the graph of elephant
population growth.
Analyze Explain how the two
graphs are similar and how they
are different, and explain why
there is a difference.
Carrying capacity is the size of a population that can be supported
indefinitely by the resources of a given ecosystem. Beyond this carrying
capacity, no additional individuals can be supported, at least not for
long. When a population is maintained at its carrying capacity, the size
of the population is maintained in balance. In a given time period, there
is a balance between the number of individuals that are added to the
population and the number of individuals that leave or die.
When one of the necessary resources is being used at a rate that
exceeds the carrying capacity of the ecosystem, the population will
eventually be reduced in size until it is once again in balance with the
available resources of its ecosystem. The limiting factor might be food,
but it could also be an abiotic factor. For example, polar bears need pack
ice on which to hunt, brook trout need rocky lake bottoms on which to
lay eggs, and flying squirrels, such as the one in Figure 7.8, need holes in
trees as places to roost.
The impact of limiting factors on exponential growth has been seen
with the population of the northern fur seal. In the 1800s, the fur trade
led to a drastic reduction in the northern fur seal population. Its decline
prompted the first international treaty ever designed to conserve wildlife,
which was signed in 1911. As shown in the graph in Figure 7.9, the fur
seal population underwent exponential growth following protection, but
eventually levelled out at the ecosystem’s carrying capacity.
Fur Seal Population Growth
Breeding Male Fur Seals
(thousands)
carrying capacity the size
of a population that can be
supported indefinitely by
the available resources and
services of an ecosystem
9
8
7
6
5
4
3
2
1
0
carrying
capacity
exponential
growth
1915
1925
1935
1945
Year
290
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Estimating Carrying Capacity
White-Tailed Deer Population (1983–2003)
Population Estimate
Sometimes wildlife biologists and park or resource
130 000
120 000
managers need to know the carrying capacity
110 000
of populations they are studying or managing.
100 000
Measuring the number of individuals in a population 90 000
80 000
can be done directly, such as by counting the
70 000
60 000
individuals. However, some populations must be
50 000
measured indirectly, as is the case with Nova Scotia’s 40 000
0
population of white-tailed deer. A method referred to
1995
1999
2003
1983
1987
1991
1993
1997
2001
1985
1989
as the Pellet Group Inventory (PGI) was developed
Year
to monitor the deer population in Nova Scotia.
In the spring, after the snow melt and before the re-growth of plants,
Figure7.10 The graph shows the
results of the data collected through
staff from the Department of Natural Resources would walk specifically
the PGI concerning deer population in
defined areas and record the number of deer pellet piles. The numbers
Nova Scotia.
were used to calculate the density of the deer population. As shown in
Infer What are some possible reasons
the graph in Figure 7.10, it was concluded that the carrying capacity of
for the drop in the population after it
the deer population was reached and exceeded in the mid-1980s, when
reached carrying capacity? Could the
population reach carrying capacity
population numbers were the highest.
again? Explain your reasoning.
F i nd Out A CTIV ITY
7-2A Graphing Population Change
How have bird populations in Canada changed over the years? To make sure that a population is sustainable, wildlife
managers and sometimes citizens do surveys to find out if the population is stable (in balance), growing, or declining. In this
activity, you will graph and analyze the results of surveys for three species.
Materials
BirdCount:1983–2007
Year
• 3 pieces of graph paper
• ruler
Downy
Woodpecker
Mourning
Dove
Ruffed
Grouse
1983
26
114
13
1985
27
119
14
1987
37
124
11
1989
35
211
11
1991
40
247
5
3. Using the line of best fit, extrapolate to the year 2020.
1993
29
242
2
What Did You Learn?
1995
29
325
4
1997
50
190
3
1. Describe the population growth of each species using
the terms “increasing,” “decreasing,” and “balance.”
1999
29
264
6
2001
24
402
5
2003
16
182
4
2005
38
416
2
2007
36
226
9
What to Do
1. Plot the data for the survey results on three pieces of
graph paper (one per species). Determine the proper
scale to use for each graph.
2. Draw a line of best fit to estimate the pattern of the
data.
2. Identify two factors that could affect the declining
species.
3. Identify two factors that could affect the increasing
species.
4. Is extrapolation using a straight line likely to be
reliable for many decades in the future? Why or why
not?
Source:AudobonChristmasBirdCount,1983–2007
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Interactions Among Species
Suggested Activity
Investigation 7-2D: What
Happens When Food Is
Limited?
Resource needs and abiotic factors are not the only influences on
population growth and size. All organisms interact with other species in
multiple ways, and these interactions can have positive and negative effects
on a population. Recall from Table 7.1 that predation, competition,
and symbiosis are the major types of interactions among species. These
interactions, along with other limiting factors, restrict populations to
particular places, roles, and sizes in the ecosystems they occupy.
A Species’ Ecological Niche
ecological niche the way
an organism occupies a
position in an ecosystem,
including all the necessary
biotic and abiotic factors
Species spend most of their time doing two things: surviving and
reproducing. They do not have “jobs” in the familiar sense—having
obligations or responsibilities to their ecosystem. As they pursue their
daily activities, however, they consume food and interact with other
species. Thus, they have jobs in the sense of providing benefits to their
ecosystem. The resources that are used by an organism, the abiotic
limiting factors that restrict how it can survive, as well as the biotic
relationships that it has with other species all make up an organism’s
ecological niche. For the little brown bats shown in Figure 7.11, the
biotic niche factors include all the insects that they eat, their competitors,
such as the common nighthawk, and their predators. The abiotic niche
factors include the places they use for roosting and hibernation, the time
of night they hunt for food, the airspace they fly through when hunting,
and the temperature range they can tolerate.
Different species provide many different services to their ecosystems
by occupying their ecological niches. These services may include the
regulation of population sizes of
other organisms, as well as specific
services related to matter cycling or
energy flow. For example, one likely
ecological service provided by the
little brown bat is the regulation of
insect populations. Cave-dwelling
bats also regulate insect populations,
but another service they provide
is to support many cave-dwelling
organisms. The food webs that
support these organisms are dependent
on nutrients that are brought into
the caves through bat droppings.
No two species can occupy the exact
same ecological niche or provide the
exact same services to their ecosystem,
because no two species live in exactly
the same way.
Figure7.11 The space these little brown bats take
up while sleeping in a cave is part of their ecological
niche.
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Human Niches and Population
Carnivorous plants, such as the pitcher plant and thread-leaved sundew
shown in Figure 7.12, are well-adapted for living in a bog. Bogs have
a lot of water and sunlight, which are two things that plants need. The
water and soil, however, are acidic and deprived of nutrients, such as
nitrogen, due to poor water flow. By consuming insects, bog plants
are able to get the nutrients they need to survive. Most bog plants are
uniquely adapted to occupy niches that are limited by these conditions.
If they were moved to a habitat with different conditions, they likely
would not survive. The fact that most organisms are limited to particular
niches is partly why different species are only found in specific types of
ecosystems in specific parts of the world. But what about the human
ecological niche?
A
Figure7.12 Both of these plants are
adapted to capture insects for extra
nutrients that cannot be absorbed
from the soil. (A) The pitcher plant has
a tubular leaf that holds water. The
moth will be broken down by digestive
juices in the water. (B) The sundew leaf
is sticky and can curl over a trapped
insect.
B
The Human Niche
Humans cannot run as fast as pronghorn antelopes or move through
water as efficiently as dolphins. Humans do not have big teeth or big
claws, like those of the black bear, or the poisonous venom of a snake.
What humans do have is a brain that has allowed us to move out of the
narrow niche that was inhabited by our ancient ancestors. By building
complex tools, controlling external forms of energy, and expanding our
use of resources, humans have been able to live successfully in many
different ecosystems, including desert and arctic ecosystems. Unlike other
organisms, we have constructed our own niche.
For humans to continue to occupy such a broad niche, we must use
the ecosystems we inhabit and the resources they contain in a sustainable
way. Sustainable use of a resource is use that does not cause long-term
depletion of the resource, or affect the diversity of the ecosystem from
which the resource is obtained. Sustainable use of a resource, whether
it is water or an entire ecosystem, allows the resource to meet the needs
of present and future generations. If humans do not use resources in a
sustainable way, our niche may shrink again over time.
sustainable use use that
does not lead to long-term
depletion of a resource, or
affect the diversity of the
ecosystem from which the
resource is obtained
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Humans and Carrying Capacity
The populations of most species are regulated by the carrying capacity
of the ecosystems that the species occupy. Early humans were regulated
by the carrying capacity of their ecosystems. More recently, however, the
intellectual abilities of humans have allowed us to create our own niche, as
well as increase the carrying capacity of the biosphere for our population.
From early developments, such as using fire and making simple tools and
weapons, humans have progressed to exploiting huge amounts of energy
and resources to run complex, modern societies.
Recall that the populations of all species, including humans, tend to
increase exponentially until their carrying capacity is reached. Human
exploitation of natural resources has produced improvements in public
health, education, agriculture, medicine, and technology. Because these
improvements have increased the carrying capacity for humans, the human
population has increased, as shown in Figure 7.13.
Until about 400 years ago, human population growth had been steady
but not explosive. At that time, the population was about half a billion
people. It had taken about 650 years for the population to double from a
quarter-billion. In the early 1800s, the human population reached
1 billion—a doubling time of only 200 years. The present doubling time
is about 60 years.
Earth’s human population currently stands at around 7 billion. No
one knows what the sustainable carrying capacity is for humans, but it
is closely linked to energy. This is because highly productive agriculture
requires large expenditures of energy. Many scientists believe that the
biosphere’s carrying capacity is unlikely to be able to sustain the 12 billion
people expected by the end of the century.
A
World Population (last 2000 years)
B
World Population (last 1000 years)
1
6
4
3
1400
2
Billions of People
major scientific
advances
0.5
beginning of
Industrial Revolution
1
deadly
plague
0
Year
00
20
00
00
16
00
14
00
12
00
10
00
16
00
18
00
20
00
00
14
12
0
00
10
0
80
0
60
40
20
0
0
18
Billions of People
5
Year
Figure 7.13 Earth’shumanpopulationhasbeenslowlygrowingforthousandsofyears.Sinceabout
1750,therateofgrowthhasincreaseddramatically.
Explain What event caused a decrease in human population? Why would changes beginning around
1750 result in such rapid increase?
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Check Your Understanding
5. How have humans been able to occupy a broad niche?
6. What is sustainable use?
7. What is the current doubling time of the human population?
Ecological Footprints and Carrying Capacity
Altering an ecosystem so that more energy and resources can be
consumed is only one way to increase the carrying capacity of the
ecosystem. The second way to increase its carrying capacity involves
altering behaviour, rather than the ecosystem itself.
An ecological footprint is a measure of the impact of a human
individual or population on the environment. Data used to measure an
ecological footprint include energy consumption, land use, and waste
production. An ecological footprint reflects the behaviour of individuals
and the communities they live in. It is a measure of the productive land
and water that are needed to support an individual’s standard of living
forever.
The average person in developed countries, which include Canada,
has one of the largest ecological footprints in the world, as shown in
Figure 7.14. Ecological footprints this large in a world that has finite
(limited) resources and is dependent on non-renewable fossil fuels are
likely to be unsustainable. The increasing world population is putting
stresses on ecological support systems. As the ecological footprints of
people in developing nations also increase in size, these stresses will be
multiplied. Modern societies must seek to establish ecological footprints
that reflect the principles of sustainability—use of Earth’s land and water
at levels that can continue forever. Ways that individuals can reduce their
ecological footprint include consuming fewer resources or using existing
resources more efficiently through technological innovation, energy
efficiency, and recycling.
unsustainable a pattern
of activity that leads to a
decline in the function of
an ecosystem
sustainability use of
Earth’s resources, including
land and water, at levels
that can continue forever
Ecological Footprints
10
8
6
4
global
average
2
0
U
De SA
nm
a
Ire rk
la
Au nd
str
a
Ze N lia
ala ew
n
Ca d
na
d
Fr a
Ho anc
ng e
K
Ge ong
rm
an
y
Ne U
th K
er
lan
ds
So Jap
ut an
h
A
Ar frica
ge
nt
M ina
ala
ys
ia
Ch
ina
In
dia
Hectares per Person
12
Countries
Figure7.14 Ecological footprints are often measured by the amount of land that is required each
year per person.
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What Is the Carrying Capacity of Humans?
Suppose one day you walk into your science class and find that the
number of students has doubled. Your classmates are sitting on desks
and on the floor, because there are not enough chairs. You find a seat,
but you cannot see the board. You have to share a textbook with four
other students. Your once-efficient classroom environment is not working
anymore. There are not enough resources to support and sustain the
number of students in it. You read earlier that it is important for scientists
to know the carrying capacity of other species. For centuries, scientists
have been asking that question about humans.
In the 1600s, scientists estimated the carrying capacity of humans to
be between 6 and 13 billion. More modern estimates have ranged from
1 to 2 billion people living in relative comfort with all of the resources
they need to 33 billion people living with minimum resources for survival.
Many scientists currently place human carrying capacity at about
12 billion people.
Because humans can carry their biomes with them as a result of
science and technology, we can exploit multiple niches simultaneously
and can increase our carrying capacity to a certain point. However, some
scientists argue that we have already exceeded it. If that is the case, what
does that mean? Could we exceed our carrying capacity indefinitely?
7-2B Supporting a Country’s Ecological
T hi nk Abou t It
Footprint
The map shows the land area of the Netherlands compared
to the theoretical area the Netherlands would need to be
to support its ecological footprint. In this activity, you will
calculate some examples of this concept using different
countries.
Materials
• print and/or Internet resources
What to Do
1. Compare the land area of the countries in Figure7.14
with the theoretical area each country would have to
be to support its ecological footprint. To do this, choose
three of the countries from the graph and research
the land area and current population statistics for the
countries.
2. For each country you chose, multiply the population
information you found in step 1 by the hectare per
person value from the Figure7.14.
3. In a table, record the actual land area, population,
and theoretical area the country would need to be to
support its ecological footprint that you calculated for
each country.
296
What Did You Find Out?
1. Compare the area for each country to the calculated
area it would need to be to support its ecological
footprint. Was the theoretical area larger than the
actual land area? If so, what does this mean in terms
of sustainability?
2. If the theoretical area was smaller, what does this
mean for the sustainability of that country? Can
you assume that, because the ecological footprint is
smaller, everyone in that country has the resources they
need to survive? Why or why not?
Netherlands
Germany
France
Poland
Netherlands
Ecological
Footprint
Spain
The land area of the Netherlands is about 34 000 km2. However,
the area of its ecological footprint is about 15 times larger.
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7-2C Populations and Sustainable
Ecosystems
SkillCheck
• Collecting Data
• Graphing
• Analyzing Data
• Communicating
Safety Precautions
• Use caution when working
with the sharp pencil to
make holes through poster
paper.
Materials
• 2 sheets of white poster
paper (32 cm  32 cm each)
• ruler
• sharp pencil
• 32 square green sticky notes
(4 cm  4 cm each)
• bag of 100 checkers or
similar objects (50 black and
50 red)
• calculator
• graph paper
Conduct an InVesTIgATIOn
One goal of a park manager is to maintain the resources of the park for the benefit
of all its users over many years. An increase in demand for resources by any species
affects all the other users of the park. Knowing the population size, carrying capacity,
and other factors about a population, such as white-tailed deer, helps resource
managers assess the health of the herd as well as make decisions about hunting
regulations. In this investigation, you will play the role of park manager. Your job is
to help maintain the deer population at or near the park’s carrying capacity for deer.
Recall that the carrying capacity is the maximum number of individuals of a species
that an ecosystem can sustain.
Question
What factors might affect the balance of a population, leading it to become out of
balance with the carrying capacity of the ecosystem?
Procedure
1. Your teacher will provide you with a procedure for this investigation.
Analyze
1. Was there a trend in the deer population in your park? Explain.
2. If you experienced a consistent increase or decrease in deer numbers, explain the
main reason for this change. How could you achieve a more stable population?
3. Did different parks experience different results? If so, suggest the main cause of
the differences.
4. How are the factors that determine the size of a deer population in a park
similar to the factors that determine the human population of Canada? How are
they different?
5. Over the past two centuries, the numbers and distribution of deer in parts of
North America have varied greatly as a result of human activities. How would
each of the following activities affect deer numbers?
a. deforestation
c. removing predators
b. reforestation
d. restricting hunting
Conclude and Apply
1. Local conservation groups want to re-introduce wolves, which are predators of
deer, into your park. As park manager, explain why you would agree or disagree
with the proposal. List various effects that a population of wolves might produce
in your park.
2. Suppose that you need to monitor the population of real deer in a park over a
10-year period. What methods would you use to measure the population? How
often would you do a population count? What other data could you track that
may affect population numbers?
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7-2D What Happens When Food Is Limited
SkillCheck
• Using a microscope
• Observing and Recording
• Graphing
• Analyzing and Predicting
Paramecia (paramecium, singular) are unicellular organisms that are commonly found
in freshwater ponds and marshes. They are covered in fine hair-like structures, which
they beat to move themselves around and to sweep bacteria and other small food
particles into a pore that serves as a mouth. In this investigation, you will study the
factors that limit the growth of a paramecium population in a given volume of water
over three weeks.
Question
Safety
How are population size and growth related to food supply?
Procedure
• Remember proper techniques
for using a microscope,
including handling the
microscope with care.
• If you have a mirror on the
microscope, do not direct it
toward the Sun.
Materials
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
2 plastic cups with labels
felt marker
50 mL graduated cyclinder
paramecium culture
medicine dropper
yeast culture
toothpicks
methyl cellulose
6 microscope slides
scissors
30 cm cotton thread
tweezers
6 cover slips
light microscope
plastic wrap
2 rubber bands
distilled water
1. Make two copies of the data table below. Title one “Added Food” and the other
“Limited Food.”
Day
NumberofParameciainSample
Slide1
Slide2
AverageNumber
ofParamecia
Slide3
1
3
5
2. Label one cup “added food” and the other cup “limited food.” Using the graduated
cylinder, carefully measure 10 mL of paramecium culture into each plastic cup.
3. Using the marker, draw a line on each cup to indicate the level of the water.
4. Add one drop of yeast culture into the cup labelled “added food.”
5. Using a toothpick, smear a small amount of methyl cellulose in the middle of each
of three slides. The methyl cellulose should cover an area that is roughly the size of
a cover slip.
6. Cut the thread into 12 pieces, each about 5 mm long.
7. Using the tweezers, place four pieces of cotton thread on each slide. These threads,
together with the methyl cellulose, will be obstacles for the paramecia to slow
down their movement enough for you to count them. Number each slide.
8. Place on each slide one drop of paramecium culture from the cup labelled “added
food.” Put a cover slip over the drop on each slide.
9. Using the low power of the microscope, count the number of paramecia in one
field of view on each slide.
10. Record your counts in your data table for added food. Calculate and record the
average.
11. Repeat steps 5 to 10 for the culture in the cup labelled “limited food.”
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Conduct an InVesTIgATIOn
12. Cover each cup with plastic wrap, and secure the plastic wrap with a rubber band.
Make several small holes in the plastic wrap so that air can enter.
13. Clean your slides and cover slips in preparation for the next samples. Repeat steps
5 to 11 every two days (or more, as your teacher directs). Always wash your hands
after completing the procedure.
14. Add an equal amount of distilled water to each cup every few days to keep the
water level constant.
15. After three weeks, make a line graph of your data for each culture. Put “Average
Number of Paramecia” on the y-axis and “Time (days)” on the x-axis.
Analyze
1. Why did you count three samples for each culture, rather than one sample?
2. Compare the shapes of your graphs. What can you infer about the role of food in
limiting population growth?
Conclude and Apply
1. Predict the effect of doubling the amount of food added to a paramecium culture.
Explain your answer.
2. You counted the paramecia in one field of view to estimate changes in the
population size over time. Outline a method you could use to estimate the size of
the entire population of paramecia in each cup.
3. The following graphs show the results of an experiment with two species of
paramecia. This experiment was first carried out by population biologist G. F.
Gause. He observed the growth of populations of these two species when each
population was grown alone and when the two populations were grown together.
Study the two graphs, and answer the following questions.
Number of
Paramecia
(per mL)
Paramecium aurelia
800
400
<
grown alone
0
Time
mixed
culture
Number of
Paramecia
(per mL)
Paramecium caudatum
200
100
0
grown alone
mixed
culture
Time
(a) What is the carrying capacity for each of the two species, Paramecium aurelia
and Paramecium caudatum?
(b) What happens to the carrying capacity of each paramecium when the two
species are mixed?
(c) What can you infer about each species of paramecium’s ability to compete?
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Sable Island National Park
Wild horses and endangered roseate terns are just a few of the
organisms that make Sable Island a unique ecosystem.
There are few places in the world today that remain
relatively untouched by human footprints, both literally
and ecologically. One of these, located 300 km south-east
of Halifax, is Sable Island. Due to harsh living conditions,
no human settlements on the island have been
permanent. Humans have left their mark on the island,
however. Over 350 ships have been wrecked on the
shores of Sable Island, due mainly to the island’s shallow
coastline and fog. Construction of twin lighthouses on the
island in the 1800s has since made this “graveyard of the
Atlantic” safer for mariners.
Today, the island’s wind-and wave-swept dunes are
best known as the home of several hundred wild horses.
These horses have lived on the island for over 300 years.
Once belonging to Acadian settlers, they were put to
pasture on Sable Island after the settlers were deported
to the American colonies in the 1700s. Because of their
isolation, the horses are small, rugged animals that are
well adapted to life on Sable Island, where food and
water are scarce. Feeding on the tough marram sand
grass and digging for water in the dry season, the horses
manage to survive these conditions.
300
Sable Island is also home to many other organisms.
Marram grass is the dominant plant in this ecologically
fragile grassland ecosystem. However, the island and the
ocean surrounding it support a much greater diversity
of animal life. Several species at risk—species that are
in danger of becoming extinct in Canada—reside here.
Sable Island is a haven for sea birds and other migrating
bird populations. Canada’s endangered roseate tern is
one of these birds. Numbering less than 300, roseate
terns are found only on Sable Island and a few other
islands off the coast of Nova Scotia. The waters around
the island also host many predator and prey species. It is
in these waters that 18 shark species feed on the largest
colony of grey seals on Earth.
In October 2011, Sable Island was designated
a national park. As a result, the island’s sensitive
ecosystems and at-risk species are now protected from
human impact by Parks Canada. This protection also
applies within 1 nautical mile (1.852 km) of its shores.
Currently, about half the species at risk in Canada are
protected in national parks, national wildlife areas, and
national marine conservation areas.
Questions
1. Parks Canada manages public access to national
parks to protect the ecosystems and species found
there. However, some conservation organizations
are concerned that designating Sable Island as a
national park will actually draw more visitors to
this area.
(a) Describe three ways in which visitors to
Sable Island could harm local organisms and
ecosystems.
(b) Do you think that designating Sable Island as
a national park is a positive move in terms of
ecosystem and species conservation? Explain
your reasoning.
(c) Write a brief proposal explaining how you
would manage visitor access to Sable Island in
order to reduce human impact on the island.
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Checking Concepts
1. Define and give an example of a population.
2. Explain why exponential growth is not
sustainable in nature.
3. What are some examples of limiting factors in
ecosystems?
4. Use a T-chart to compare and contrast
density-independent factors and densitydependent factors.
5. Use pictures and words to explain carrying
capacity.
6. How would the removal of dead timber from
an area affect the carrying capacity for flying
squirrels?
7. What is an ecological niche?
8. Use a Venn diagram to compare and contrast
an ecological niche and a job.
9. What adaptation allows bog plants to live in a
bog? Why do they need this adaptation to live
in a bog?
10. What has the human brain allowed us to do
to our ancestral niche and to our original
carrying capacity?
11. What are the two ways that carrying capacity
can be increased?
12. What is the difference between sustainable
and unsustainable use?
13. What is the probable carrying capacity of
humans?
15. Analyze what would happen to a niche if the
resources and energy in the ecosystem were
not sustainable.
16. Sketch what you consider to be your own
personal niche.
17. Draw a footprint in your notebook. At each
toe, write one thing you do that reduces
your ecological footprint. At the heel of your
footprint, write the one thing you do (or
don’t do) that causes your greatest ecological
impact. Across the middle of your footprint,
write the one thing you would find most
difficult to change to shrink your ecological
footprint.
18. The table below contains data about the
ecological footprints of different countries.
EcologicalFootprints
0.1
Brazil
2.1
Ethiopia
0.8
Japan
5.9
Russia
4.4
United Kingdom
United States
14. The graph below shows how a population of
water fleas changed over time. The data were
collected in a laboratory situation. Explain
how the population changed, using the terms
“carrying capacity,” “exponential growth,”
and “limiting factors.”
Water Flea Population Over Time
150
EcologicalFootprint
(hectaresperperson)
Afghanistan
United Arab Emirates
Understanding Key Ideas
Number of Water Fleas
(per 50 mL)
Country
11.9
6.3
12.3
(a) Construct a bar graph of the data.
(b) Which countries have the largest
ecological footprint per person? Which
have the smallest ecological footprint per
person?
(c) Why do you think there are such large
differences in the footprints of these
countries?
Project Prep
120
90
60
30
0
40
80 120
Time (days)
160
How can the growth of the human population,
which can lead to more electronic products
being manufactured, affect the sustainability of
ecosystems?
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<C
7.3 How Human Activities Can
Affect Sustainability
What Do You Think?
• Why is it important to understand that ecosystems are connected?
• How could climate change affect the sustainability of ecosystems worldwide?
• Why is it important to consider the possible consequences of releasing chemicals
into the environment?
Key Terms
eutrophication
greenhouse gases
greenhouse effect
trophic level
biomass
trophic efficiency
bioaccumulation
Matter and energy are recycled through all four of Earth’s systems—the
lithosphere, the hydrosphere, the atmosphere, and the biosphere. All the
matter that Earth has ever had and ever will have has been present since
its formation over 4 billion years ago. Except for the occasional meteorite
impact, no new matter is ever added to the planet and no matter ever
disappears. Instead, the same matter is used and reused in an everrepeating pattern of cycles.
These cycles make essential matter, such as carbon, nitrogen,
phosphorus, sulfur, oxygen, water, and many other nutrients, continuously
available to terrestrial and aquatic ecosystems, thus connecting all ecosystems
at a global level. However, at local levels, due to human activities in
particular, the availability of nutrients in any given ecosystem can be reduced
and/or increased. That affects the balance among biotic and abiotic parts of
that ecosystem, and thus can compromise its sustainability.
Nutrient Cycles and the Sustainability of Aquatic
Ecosystems
eutrophication a process
in which nutrient levels in
aquatic ecosystems increase,
leading to an increase in
the populations of primary
producers
302
Many human activities affect the nitrogen cycle. For instance, nitrogen is
a key part of fertilizers. Farmers and gardeners use fertilizers to enhance
the growth of their plants. However, not all the nitrogen in the fertilizers
is used by the plants. Some stays in the soil. When it rains, or when fields
are watered, some of the nitrogen is carried into aquatic ecosystems. This
excess nitrogen can cause an overgrowth of algae called an algal bloom.
In the mid-20th century, many aquatic ecosystems developed excessive
algae growth. In Lake Erie, the amount of algae increased by as much
as 30 times, upsetting natural balances. The process of eutrophication
[pronounced u-tro-fi -KAY-shun], in which deposits of excess nutrients
cause an overgrowth of algae, is very slow when natural. The alarming
rate of eutrophication during the mid-20th century suggested, however,
that human activities were the cause.
In 1968, a series of experiments with worldwide importance was
designed involving 58 of the thousands of lakes in the province of
Ontario. These 58 lakes were chosen to be the Experimental Lakes Area
(ELA). Government and university researchers from around the world
used this area for experiments to understand more about lake ecology.
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Ecologists added large volumes of different nutrient combinations to the
lakes. They found that when excess phosphorus was added to the water,
the result was eutrophication, as shown in Figure 7.15.
How does excess phosphorus end up in bodies of water? As is the
case with nitrogen, not all the phosphorus in fertilizers that are applied
to farmlands are taken up by the crop plants. So, excess nitrogen and
phosphorus enter the ground and are transported by water to nearby
aquatic ecosystems. Figure 7.16 illustrates the steps involved in
eutrophication, as well as its consequences.
normal phosphorus levels
<C
La
–p
<p
is
tha
SC
barrier
excess phosphorus
1 Fertilizer runs off from farmland into water.
Figure7.15 Ontario’s Experimental
Lakes Area was used to learn more
about the causes of eutrophication.
Describe How does the side of the
lake with excess phosphorus look
different than the side of the lake
with normal phosphorus levels?
2 Algae bloom.
<C
ON
be
3 Submerged plants die due to reduced light.
4 Algae and other plants die.
5 Bacteria use oxygen during decomposition.
6 Oxygen levels in the water drop
too low for fish to survive.
Figure7.16 When nutrients that are normally limited are added in excess amounts, the balance in an
aquatic ecosystem is upset by eutrophication.
Infer What actions could be taken to help reduce the incidence of eutrophication? Explain your
reasoning.
Check Your Understanding
8. What is eutrophication?
9. Which nutrient was found to be the main cause of eutrophication
in northern Ontario lakes?
10. What is one possible source of excess phosphorus in aquatic
ecosystems?
11. Suppose that you have a small fishpond in your backyard. You work
hard to get your lawn looking thick and green. By the end of the
summer, your lawn looks great, but the water in your fishpond is
green and the fish are dead. Infer what happened.
Word Connect
The term eutrophic comes
from the Greek word
euthophos, which means well
nourished.
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Carbon Dioxide and Other Greenhouse Gases
greenhouse gases
atmospheric gases that
prevent heat from leaving
the atmosphere, thus
increasing the temperature
of the atmosphere
greenhouse effect the
warming of Earth as a
result of greenhouse
gases, which trap some
of the energy that would
otherwise leave Earth
Greenhouse gases are atmospheric gases that prevent heat from leaving
the atmosphere, thus increasing the temperature of the atmosphere. They
include water vapour, carbon dioxide, and methane. Without greenhouse
gases, Earth’s temperatures would average less than 0ºC. This natural
insulating capacity of greenhouse gases is known as the greenhouse
effect.
Fossil Fuels
Based on fossil evidence, scientists have concluded that single-celled
organisms used photosynthesis to generate biological material more
than 3 billion years ago. Most of this matter has been cycled through
the biosphere countless times. Small amounts, however, escaped the
biosphere’s cycling system when the remains of organisms settled in
places where there was not enough oxygen to decompose them. Over
time, with pressure and heat, the material changed into fossil fuels such as
coal, petroleum, and natural gas. Burning fossil fuels involves a chemical
reaction that consumes oxygen, and releases energy and carbon dioxide.
Enhanced Greenhouse Effect
Fossil fuels have been accumulating for many millions of years. However,
significant portions of Earth’s reserves have been burned by humans in the
span of only a few centuries. Because humans have “suddenly” released
much of the carbon dioxide that ancient plants converted to biological
material, the net result for the atmosphere is added carbon dioxide.
Figure 7.17A shows that since the Industrial Revolution, which began
in the mid-1700s, the concentration of carbon dioxide in the atmosphere
has increased. The Industrial Revolution marked the start of increased
and widespread burning of fossil fuels as a source of energy for many
countries around the world. Many scientists hypothesize that the increased
concentration of carbon dioxide in the atmosphere, along with an increase
in other greenhouse gases, such as methane, is the cause of the increase
in Earth’s average surface temperatures that contributes to global climate
change. Figure 7.17B shows that as the amount of carbon dioxide in
the atmosphere has increased, so has Earth’s average surface temperature.
Table 7.3 lists some of the ways in which excess carbon dioxide in the
atmosphere and in the ocean can affect the sustainability of ecosystems.
380
370
360
350
340
330
320
310
300
290
280
0
<280
304
B
Carbon Dioxide Concentration vs. Year
Change in Global Temperature Over Time
0.8
Difference from Average
Temperature ( ˚ C)
Figure7.17 (A) Since the Industrial
Revolution, carbon dioxide levels
have risen steadily. (B) Earth’s
average surface temperature has also
increased by about 0.74°C.
Concentration of Carbon Dioxide (ppm)
A
0.6
0.4
0.2
0
– 0.2
– 0.4
– 0.6
1900
1920
1940
pre-industrial carbon dioxide
concentration (<280 ppm)
1960
Year
1980
2000
– 0.8
1850 1870 1890 1910 1930 1950 1970 1990
Year
Sources: Climatic Research Unit and Hadley Centre, 2008
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Table 7.3HowImbalanceintheCarbonCycleAffectsSustainability
Example
Photo
EffectsonSustainability
Excess
Carbon
Dioxide in
Atmosphere
Excess carbon dioxide in the atmosphere can lead to increased temperatures at Earth’s
surface, which can affect the sustainability of ecosystems in several different ways,
including
• a change in the length of growing seasons
• the introduction of new pests or diseases to an ecosystem
• a loss of habitat or food sources in an ecosystem
• a change in the frequency and intensity of extreme weather events, such as floods,
droughts, heat waves, and cold snaps
Excess
Carbon
Dioxide in
Ocean
Excess carbon dioxide in ocean water acts as an acid, reducing the pH of seawater so it is
more acidic. Even a small change in pH can interfere with important processes in marine
organisms:
• shell growth in organisms that absorb calcium carbonate from seawater to make shells,
such as corals, mollusks, shrimp, lobster, and phytoplankton can be reduced
• the photo on the left shows how the shell of a mollusk deteriorated over time when
placed in laboratory seawater with increased acidity
• scientists hypothesize that some species of fish may have lower reproductive success as a
result of the increased acidity
Reducing Carbon Dioxide in the Atmosphere
There are many ways to reduce the amount of carbon dioxide being
released into the atmosphere. These include international initiatives by
governments from around the world, initiatives by the federal, provincial,
and local governments of Canada, and efforts by individuals. Three
examples of efforts to reduce carbon dioxide are discussed below.
• The Kyoto Protocol is an international agreement to reduce
greenhouse gas emissions, which was signed by over 180 countries.
To meet the terms of the Protocol, countries can reduce emissions
or get credits for removing carbon dioxide from the atmosphere
by planting trees in non-forested areas. Since plants remove carbon
dioxide from the atmosphere, large areas of trees and other plants,
such as forests, are known as carbon sinks.
• Boreal forests in Canada cover over 1 billion acres and are thought
to be the single-largest terrestrial sink for carbon dioxide on Earth.
In July 2008, the premiers of Ontario and Québec announced that
each province would protect roughly half of its boreal forests. Many
organizations, including conservation groups, First Nations, and
private companies, have joined the Boreal Conservation Framework,
which calls for the protection of at least 50 percent of all of Canada’s
boreal forests.
• Recycling helps to reduce carbon dioxide emissions because, in
most cases, less energy is needed to make something from recycled
materials than from new materials. Since 1996, Nova Scotia has
banned the disposal of certain beverage containers, including
aluminum cans, and glass, plastic, and steel containers, in provincial
landfills. As a result, by 2011, more than 3 billion beverage containers
in Nova Scotia have been recycled.
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Trophic Levels
trophic level a category of
organisms that is defined
by how the organisms gain
their energy
Recall from earlier studies that matter and energy are transferred between
trophic levels within the biosphere. A trophic level is a category of
organisms that is defined by how the organisms gain energy. Examples of
trophic levels include primary producers and consumers. Primary producers
are organisms, such as plants, that can make their own food. Consumers are
organisms that cannot make their own food. Consumers must eat other
organisms to get the matter and energy they need to survive.
Trophic Efficiency
biomass the total mass
of living organisms in a
defined group or area
trophic efficiency a
measure of the amount of
energy transferred from
one trophic level to the
next higher trophic level
Biomass is the mass of living cells and tissues that has been assembled by
organisms using energy from the Sun. Leaves, stems, wood, roots, and
flower nectar are all packed with chemical energy that has been converted
from solar energy. Animals indirectly rely on solar energy too, by eating
plants or other animals that eat plants.
Trophic efficiency is a measure of how much of the energy in
organisms at one trophic level is transferred to the next higher trophic
level. Trophic efficiencies are usually quite inefficient—they average
only about 10 percent and often much less. This is because organisms
use much of the energy from the biomass they consume for their life
functions, and they produce wastes as well. Energy is also lost as heat
from the bodies of organisms.
Figure 7.18 shows the transfer of energy from a primary producer,
grass, to a tertiary consumer, the great horned owl. Suppose that the
grass biomass contains 1000 units of energy. If only 10 percent of this
energy is transferred to the jackrabbit, only 100 units of energy will reach
the jackrabbit. Of these 100 units, only 10 will be transferred from the
jackrabbit to the long-tailed weasel. Of the 10 units that reach the weasel,
only 1 unit of energy will reach the great horned owl.
tertiary consumers
(top carnivores)
1 energy unit
secondary consumers
(carnivores)
great horned owl
long-tailed weasel
10 energy units
primary consumers
(herbivores)
10 0 energy units
primary
producers
1000 energy units
jackrabbit
grass
Trophic pyramid
Figure7.18 Energy that is stored in biomass at one trophic level moves to the next trophic level
through a food chain.
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Water Pollution and Bioaccumulation
Bioaccumulation is a process in which materials, especially toxins,
are ingested by an organism at a greater rate than they are eliminated.
The bioaccumulation of toxins from human-made pollution can be
devastating to a species. These toxins can cause health problems or
death. Biomagnification is a process that is related to bioaccumulation.
Biomagnification is the increase in the concentration of a toxin as it
moves from one trophic level to the next.
bioaccumulation a
process in which materials,
especially toxins, are
ingested by an organism at
a rate greater than they are
eliminated
DDT
DDT (dichlorodiphenyltrichloroethane) is an agricultural insecticide that
was once used in North America. When DDT entered the environment
in run-off from land, it was absorbed by algae in the water. Microscopic
animals ate the algae, and small fish ate the microscopic animals. At each
trophic level in the food chain, the concentration of DDT in the tissues
of the organisms increased. At high concentrations, the DDT affected
reproduction in fish-eating birds. Following the ban on DDT in the
1970s, populations of DDT-vulnerable birds slowly increased in numbers
in Canada.
PCBs
PCBs (polychlorinated biphenyls) were previously used by industries.
PCBs entered water, air, and soil while they were being used and
disposed of. Figure 7.19 shows how the concentration of PCBs, given
in parts per million (ppm), is biomagnified in higher-level consumers in
a freshwater ecosystem such as a lake. Peregrine falcons were affected
by both DDT and PCBs. After PCBs were banned, peregrine falcons
were brought back from the brink of extinction by having captive birds
produce young. The young birds were then raised in boxes on the sides
of cliffs across Canada. Between 1982 and 1991, a total of 178 peregrine
falcons were released in the upper Bay of Fundy region. Since then, nine
nesting pairs have been counted in the Bay of Fundy region and over
500 nesting pairs have been spotted across Canada.
Figure7.19 The concentration of
PCBs in the tissues of organisms
increases at each trophic level. The
greatest health problems show up at
the highest trophic levels.
herring gull
124 ppm
lake trout
4.83 ppm
herring gull
eggs 124
ppm
water 0.000 002 ppm
phytoplankton
0.0025 ppm
zooplankton
0.123 ppm
rainbow smelt
1.04 ppm
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Check Your Understanding
12. Describe the greenhouse effect.
13. Make a list of actions you could take to reduce the amount of
carbon dioxide being released by the burning of fossil fuels.
14. What is the difference between a trophic level and trophic
efficiency?
15. What is bioaccumulation?
The Effects of Pollutants Travelling Within and Between
Ecosystems
As you have read, terrestrial and aquatic ecosystems are connected. The
chemicals we use on land, including fertilizers, pesticides, solvents, other
organic compounds, and heavy metals can all reach aquatic ecosystems
through surface run-off. Another example that showcases the connectivity
of terrestrial and aquatic ecosystems is that of the beluga whales in the
northern part of the St. Lawrence River. The beluga whales in this
region, shown in Figure 7.20, have some of the highest rates of cancer
of any wild animal studied. Beluga whales in the Canadian Arctic are not
reported to have cancer.
Figure7.20 Between 1983 and
1999, scientists at the University of
Montréal found that 27 percent of
adult beluga whales died from cancer,
including cancers of the stomach, liver,
and small intestine.
Did You Know?
Beluga whales are often referred
to as canaries of the sea by
sailors and scientists because of
the many clicks, whistles, and
other vocalizations they emit.
They can also mimic a variety of
sounds.
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When scientists examined the tissues of dead beluga whales from the
St. Lawrence River, they found dozens of chemicals, including PCBs,
DDT, and polycyclic aromatic hydrocarbons (PAHs). PAHs are known
carcinogens, or substances that cause cancer. Scientists hypothesize that
these and other pollutants settle in the sediment of the river, which is
where the whales feed on invertebrates, such as krill and worms. The
chemicals bioaccumulate in the whales’ tissues, leading to weakened
immune systems and high rates of cancer. Scientists from the St. Lawrence
National Institute of Ecotoxicology have also found that only 20 percent
of female beluga whales were pregnant or had recently given birth,
compared to 66 percent of female belugas in the Canadian Arctic. These
findings suggest that the chemicals may also affect the reproductive
systems of the whales.
Canadian scientist, Dr. Sylvain De Guise, also studies the tissues of
the beluga whales from the St. Lawrence River. He has found that while
a single chemical may not be toxic, a mixture of two or more chemicals
becomes toxic and can interfere with cell function. Laboratory studies
show that when cells from the immune system of beluga whales are
exposed to a mixture of chemicals commonly found in belugas in the St.
Lawrence River, the cells are unable to fight off bacteria that would cause
an infection. Immune cells that are not exposed to the chemicals are able
to produce a normal immune response to the bacteria.
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Pollution in the North
In recent years, tonnes of hazardous chemicals have
been carried northward thousands of kilometres to the
Arctic. More than 3.7 million people in eight countries are
constantly exposed to these toxins.
Persistent organic pollutants such as DDT, toxaphene,
and chlordane are applied in fields or sprayed on crops in
temperate and tropical climates, where they evaporate.
Fossil fuels, PCBs, and the heavy metals cadmium
and mercury are present in air emissions from burning
fuel for energy and from waste incineration. These toxic
substances in low concentrations are carried in warm
ocean and wind currents. They are then carried in water
vapour into the atmosphere, deposited back down in
rain, carried up again, and returned again as rain. This
process continues to move toxins up the continent until
they reach the North, where the cold locks them away.
Chemical breakdown is very slow in this area of frigid
temperatures and little sunlight. The Arctic lacks the soil
and plant life that absorb pollution elsewhere, so the
toxins remain for decades, even centuries.
Once in these cold ecosystems, the contaminants
enter food chains and bioaccumulate in fish, birds, marine
mammals, and humans. Inuit hunters are reporting
abnormalities in animals, such as seals without hair,
polar bears without reproductive organs, and seals with
burnlike holes on their skin. Researchers have found that
these toxins not only harm wildlife, but also accumulate
in the breast milk of Inuit women at levels nine times
higher than in women to the south.
Some scientists are trying to identify the properties
that cause chemicals to accumulate. Others are looking
for ways to get rid of the heavy metals left from the
disposal of electronic products. Scientists continue to
find solutions to these problems, but the once-pristine
North will continue to suffer for centuries from the
consequences of pollution that comes from far away.
Questions
1. How are toxic substances transported to the
Arctic?
2. State two ways in which contamination from toxic
chemicals harms this ecosystem.
3. What effects of contamination have been seen in
wildlife?
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7-3A Fertilizers and Algae Growth
SkillCheck
• Measuring
• Controlling Variables
• Analyzing Data
• Interpreting Data
Safety
• Wear goggles and use rubber
gloves when handling the
fertilizer.
• Follow your teacher’s
directions to dispose of the
fertilizer.
• Clean any spills immediately,
and inform your teacher.
Materials
•
•
•
•
•
•
•
•
•
•
balance
scoop
50 mL graduated cylinder
small funnel
five 250 mL beakers
liquid fertilizer that contains
nitrogen and phosophorus
algae culture
distilled water
adhesive labels
marker
Conduct an InVesTIgATIOn
Fertilizers in run-off from agriculture can add extra nutrients to aquatic ecosystems.
In this investigation, you will model what happens when fertilizer in run-off enters
aquatic ecosystems.
Question
How does fertilizer affect algae growth?
Plan and Conduct
1. Brainstorm how you could test the effects of fertilizer on algae growth.
2. Determine what your independent variable will be. What will your dependent
variable be? Will you have a control group?
3. Make a table for recording your data. How often will you make observations?
4. Ask your teacher to approve your investigation procedure, data table, and safety
precautions.
5. Carry out your investigation.
Analyze
1. What was your independent variable? What was your dependent variable?
2. Describe the changes you observed in the dependent variable, and propose an
explanation.
Conclude and Apply
1. Suppose that a large quantity of fertilizer was added to a lake ecosystem.
Suggest what might happen to each of the following populations, and explain
your reasoning.
(a) producers
(b) consumers
(c) decomposers
2. Think about the tools, techniques, and processes that you used to gather
evidence. What improvements could you make?
Algae need light to grow. Put your
beakers in a sunny location.
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Checking Concepts
1. Use a flow chart to explain what ecologists
working on the ELA discovered.
2. Use Figure 7.16 as a guide to explain why
eutrophication can be harmful to aquatic
ecosystems.
3. What is the difference between the
greenhouse effect and the enhanced
greenhouse effect?
4. Write two or three sentences to explain the
following statement: “In the last 200 years,
humans have ‘suddenly’ released previously
stored carbon dioxide.”
5. List two ways an imbalance in the carbon
cycle can affect the sustainability of terrestrial
ecosystems. Do the same for aquatic
ecosystems.
6. Why is it important to conserve forests
around the world?
7. What is the difference between a producer
and a consumer?
8. Why is it important to understand that
terrestrial and aquatic ecosystems are
connected?
9. What do scientists hypothesize is the cause of
the high rates of cancer in beluga whales in
the St. Lawrence River?
Understanding Key Ideas
10. The phosphorus cycle is an important part of
sustainable ecosystems.
(a) How can human activities affect the
phosphorus cycle?
(b) Suggest a way that eutrophication due to
human activities can be avoided.
11. Use a graphic organizer to show the links
between fertilizers, algal blooms, and the
death of aquatic organisms.
12. Farmers, fertilizer companies, governments,
and consumers all play roles in helping
to reduce nutrient pollution of aquatic
ecosystems. List positive actions that each
group could take.
13. Identify three human activities that could
restore the balance of carbon dioxide in
the biosphere. Select one activity and write
a letter to a classmate explaining why you
would choose to do that activity.
14. Calculate the units of energy at each trophic
level in the food chain below, assuming that
the trophic efficiency at each level is
10 percent.
bunchgrass
2543 energy units
grasshopper
spotted frog
red-tailed hawk
15. Use a Venn diagram to compare and contrast
bioaccumulation and biomagnification.
Include one example of each.
16. Refer to Figure 7.19. Suppose that a lake is
located beside an abandoned manufacturing
plant. Someone discovers that the plant is
leaking chemicals into the lake. The chemicals
are absorbed by phytoplankton, which are
consumed by zooplankton. Which size of fish
would you expect to have higher levels of
chemicals in their tissues: smaller fish that eat
zooplankton or larger fish that eat the smaller
fish? Explain your answer.
17. Create a cause-and-effect map showing how
human impact on a terrestrial ecosystem can
also affect an aquatic ecosystem.
Project Prep
In this section, you learned that chemicals can
bioaccumulate in the tissues of animals. How
might the release of toxic chemicals, such as
mercury or lead, during the break down of
electronic waste, affect the sustainability of
ecosystems?
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<CA
Chapt er
7
Prepare Your Own Summary
In this chapter, you have learned about the
components of sustainable ecosystems, population
growth, and how human activities can affect
sustainability. Create your own summary of
key ideas from this chapter. You may include
graphic organizers or illustrations in your notes.
(See Appendix B for help with using graphic
organizers.) Use the following headings to
organize your notes:
1. Components of Sustainable Ecosystems
2. Biotic and Abiotic Parts of Ecosystems
3. Populations and Sustainability
4. Limiting Factors and Exponential Growth
5. Humans and Carrying Capacity
6. How Humans Can Affect Sustainability
Checking Concepts
1. Explain the meaning of the term ecosystem.
2. Sustainable ecosystems “endure and
support.” Clarify what this means.
3. Choose an organism and use it to explain
how ecosystems are connected.
4. Explain how competition can affect the
health of an organism and its ability to
reproduce.
5. How could the sustainability of the
ecosystem shown in the photo below be
affected by the introduction of chemicals
from agriculture or industry?
Understanding Key Ideas
6. Explain why the plants and animals of eastern
Canada are similar to the plants and animals
of eastern Asia.
7. What causes populations to stay within their
carrying capacity?
312
8. Identify two density-independent factors and
two density-dependent factors that can affect
populations.
9. Explain how scientists estimated the
population of white-tailed deer in Nova
Scotia. Why do you think they could not
count individuals directly?
10. Explain why no two species can occupy
exactly the same ecological niche.
11. Define sustainable use and give an example
of it in action.
12. At the current rate of population increase,
how many days are necessary for Earth’s
population to increase by 34 million people
(the approximate population of Canada)?
13. What is an ecological footprint?
14. Nutrients were added at the Experimental
Lakes Area to study eutrophication. Which
nutrient had the greatest direct influence on
eutrophication?
15. What is one possible cause of the increase in
carbon dioxide in the atmosphere since the
mid-19th century?
16. Countries around the world are monitoring
carbon dioxide emissions.
(a) What is the Kyoto Protocol?
(b) How can countries reduce the amount
of carbon dioxide that they are releasing
into the atmosphere?
17. Explain why energy decreases from one
trophic level to the next.
18. Using an example from the chapter,
explain how bioaccumulation can affect the
sustainability of an ecosystem.
19. Draw a picture that you believe represents a
sustainable ecosystem. Explain all the features
in your picture that illustrate your ideas
about sustainability.
20. Many First Nations cultures believe that
humans are the only living things that
disregard the laws of carrying capacity.
Explain whether you agree or disagree with
this statement, and why.
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21. Plan (but do not actually conduct) an
investigation to find answers to one of the
questions below. Be sure to identify all
variables, the data you will need to collect,
and what method you will use to collect your
data. Decide which format you will use to
record your findings—for example, a chart.
(a) What are the abiotic and biotic parts of
your schoolyard ecosystem?
(b) How do the abiotic and biotic parts
interact with each other?
(c) What human activities have had an
impact on the ecosystem?
22. Estimate the carrying capacity for the
population shown in the graph below. Why
do you think the carrying capacity in real-life
situations is not a smooth, flat line?
Carrying Capacity
Population (millions)
1.5
raw data
1.0
0.5
1800
1825
1850
1875
Year
ResourceUseinCanadaandVietnam
Country
Canada
Vietnam
9 985 000
330 000
Population (millions)
33
84
Population density
(people/km2)
3.2
251.5
Annual electricity
use (billion KW∙h)
487
32
Oil consumption
(barrels per day)
2 200 000
185 00
Highways (km)
1 408 800
93 300
31 500
2 700
Size (km2)
Wealth generated
per person per year ($)
carrying
capacity
2.0
26. Study the following table. Identify two
factors that may help to explain why
Canadians have a larger ecological footprint
than people in Vietnam.
1900
23. Predict what would happen to a plant if
you moved it from a tropical rainforest to a
desert. Explain your prediction.
24. In developed countries such as Canada, the
birth rate and death rate are low. In the
transition from developing to developed
country, the death rate of a country always
drops long before the birth rate—usually
about two generations before. What would
this mean for population growth during the
time between the drop in death rate and the
drop in birth rate?
25. Imagine you are an ecologist who has been
called to investigate the reasons why the
population of fish in a local stream has
been declining. What tests could you do to
determine if fertilizer run-off was the cause
of the decline in the fish population?
27. List some examples of limiting factors that
affect human populations. Then answer the
following questions:
(a) Why would a government restrict the
number of children that urban couples
may have?
(b) Should governments be allowed to do
this?
(c) Construct a list of pros and cons
concerning government restrictions on the
number of children that couples may have.
(d) Summarize your points in several
paragraphs that support your opinion.
28. Suppose that you are a science writer who is
working on an article about the effects of the
biomagnification of certain chemicals. What
questions would you ask a group of scientists
who recently created a new pesticide?
Why It Matters
Draw a cartoon or a storybook for a class of
Grade 3 students that shows the impact of
one human activity on an ecosystem and that
concludes with one action everyone can take to
lessen that impact. Be creative.
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