ecosystems and change - polytech high school · 2014-11-21 · ecosystems are constantly c han gin...
TRANSCRIPT
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oveRview
In this activity, students examine case studies that describe
the impacts of various kinds of changes on four ecosystems.
Students are asked to predict what will happen to these eco-
systems in 50 years if the situations continue as described.
The concepts of ecosystem sustainability, resiliency, and bio-
diversity are introduced.
Key content
1. Ecosystems involve interactions between communities
of living things and those living things with their physi-
cal environment.
2. Ecological changes can stress ecosystems in many ways.
When the ecosystem is able to recover from or accom-
modate stress it is demonstrating resiliency.
3. Biodiversity is related to the number of species in an
ecosystem.
4. Increasing biodiversity (e.g., by adding an invasive
species) does not necessarily increase the sustainability
of an ecosystem.
5. Reducing biodiversity, especially reducing native species,
can make an ecosystem less sustainable.
Key PRocess sKills
1. Students make accurate interpretations, inferences, and
conclusions from the text.
2. Students make predictions.
MateRials and advance PRePaRation
Because many activities in this unit require the teacher to
use an overhead or data projector, make sure that one is
always available.
For the teacher Scoring Guide: GRoup InTERacTIon (GI)
Group Interaction Student Sheet 1, “Evaluating Group Interaction”
Literacy Transparency 3, “Read, Think, and Take note”
transparency of Literacy Student Sheet 5, “KWL”
transparency of a short newspaper article on any topic*
For each student 3 sticky notes*
Student Sheet 1.1, “case Study comparison”
Literacy Transparency 3, “Read, Think, and Take note” (optional)
Scoring Guide: GRoup InTERacTIon (GI) (optional)
Group Interaction Student Sheet 1, “Evaluating Group Interaction” (optional)
*Not supplied in kit
Masters for Science Skills Student Sheets are in Teacher
Resources II: Diverse Learners. Masters for Literacy Skills
Sheets are in Teacher Resources III: Literacy. Masters for
Scoring Guides are in Teacher Resources IV: Assessment.
1 EcosystemsandChangetalK it oveR • 2–3 class sessions
Copyright 2011 The Regents of the University of California
science and global issues/biology • ecology
72
teaching suMMaRy
Getting Started
• Studentssharetheirideasaboutwaysinwhichtheythink
ecosystems change.
Doing the Activity
• (LITERacy) (GI aSSESSmEnT) Introduce the GRoup
InTER acTIon (GI) Scoring Guide.
• (LITERacy) Each student in a group of four is assigned
to read a case study.
• Studentssummarizetheircasestudiesformembersof
their group.
• Groupsrecordthesimilaritiesanddifferencesbetween
the four case studies.
• Groupspredictwhatmighthappenineachcasestudy
50 years from now.
Follow-up
• Theclassdiscussestheenvironmental,economic,and
social aspects of sustainability and how these are related
to biodiversity and resiliency of ecosystems.
bacKgRound infoRMation
one of the main reasons to study ecology is to develop an
understanding of how natural systems work. It is important
to do so not only to satisfy human curiosity, but because of
the unique nature of man’s impact on the environment.
Human decisions affect ecosystems directly and indirectly, in
large and small ways, and in the long- and short-term. a
solid understanding of ecology forms a basis for informed
decisions and accurate predictions of responses to environ-
mental change.
Ecosystems are always subject to stress. Sometimes an eco-
system can react to the stress in such a way as to maintain the
status quo. Different factors provide resistance to stress on
an ecosystem. For example, an invasive species might not be
successful in an ecosystem where there is a species that preys
heavily on it. other times, a stressor can cause a series of
gradual changes that eventually alter the entire nature of the
ecosystem (see activity 17, “Ecosystem change and Resil-
iency”). However, on occasions the stress is so severe that an
ecosystem cannot recover. In such cases the effects of the
stress exceed the resiliency of the ecosystem, and the impact
is permanent and negative. Such changes can be quick and
dramatic, as with a chemical spill, or slow as with climate
change. although the causes of severe stress may be natural— for example, volcanic eruptions, in many instances they are
the result of human activity.
While there is not a straightforward linear relationship
between biodiversity and sustainability, the sustainability of
an ecosystem is reduced when the number of species in it
falls below a critical point. consequently, the level of biodi-
versity is often a useful indicator of the degree of sustain-
ability of an ecosystem. note, however, that the introduction
of invasive species can increase the biodiversity of an eco-
system while reducing the sustainability.
ecosysteMs and change • activity 1
73
getting staRted
1 This symbol represents an
opportunity to elicit students’ expe-
riences or ideas so that the subse-
quent instruction can build on or
modify their understanding. Some-
times you will uncover ideas that are
inconsistent with scientific explana-
tions but may seem logical in the
everyday world. The Teaching Sug-
gestions often provide strategies
that you can use to address these
misconceptions.
as a class, begin a KWL chart for
ecological change. The letters KWL
refer to the three sections of the
reading strategy that ask, “What do
I Know? What do I Want to Know?
What did I Learn?” KWLs help
students process and apply the
information that they encounter in
the reading. For more information
on this strategy, refer to Teacher
Resources III: Literacy. ask the class
to list changes that they have seen
in the environment as they have
grown up, what they think has
caused those changes, and what
they want to know about ecological
change and its causes. There is a
sample KWL shown below. Students
will fill in the third column in
activities 3 and 7.
consider showing a video clip or images that
illustrate environmental change in your
locality, if possible. For suggestions go to the
Science and Global Issues page of the SEpup
website (sepuplhs.org/sgi). Introduce the term
ecosystem. Have the class brainstorm the
types of changes that could affect an eco-
system and in what ways. pose the open
question, Is ecological change good or bad—or neither?
accept all answers, but each time ask students to include
supporting examples. There is no correct answer to the
question, but it may stimulate thought and illustrate stu-
dents’ grasp of environmental issues. Explain to the class
that they are going to read about how human activities and
interventions have affected (and are still affecting) four
different ecosystems.
1 Ecosystems and Change
45
ECOLOGY is the study of how organisms interact with one another and
the environment. With an understanding of ecology, people can make
informed decisions about environmental issues. Take, for example, a gardener
who is considering how to deal with an insect that is destroying her tomatoes.
To apply an insecticide she would need to know how that chemical would affect
other organisms in the yard and what would happen if the insecticide got into
the water or the soil.
A community of various organisms interacting with each other within a parti-
cu lar physical environment is known as an ecosystem. Ecosystems are constantly
changing—sometimes in gradual and hardly noticeable ways and some times rap-
idly and dramatically. Change that occurs in one part of an ecosystem will affect
other parts of the ecosystem. One of the most critical aspects of any change that
occurs in an ecosystem is how it affects the ecosystem’s sustainability. An eco-
system is sustainable if it can support its diversity and ecological processes
through time.
ChallengeHow does change affect ecosystems?�
Wildlife and humans livetogether in many ecosystems.
1
Ecological Change KWL
Know Want to know Learned
• Humanshavechangedtheenvironment(cutdownrainforests,builtbuildings,pavedroads).
•Naturalphenomenahavechangedtheenvi-ronment(volcanoes,earthquakes,tsunamis).
• Habitatrestora-tionprojectscanhelprestoretheenvironment.
• Howmuchoftheenvironmenthavepeoplechanged?
•Whatcanbedonetorestoretheenvironment?
•Whathappensifwedon’trestoretheenvironment?
• Howmuchdoestheburningoffossilfuelschangetheenvironment?
74
science and global issues/biology • ecologyscience and global issues/biology • ecology
74
doing the activity
2 (LITERacy) (GI aSSESSmEnT)
Introduce the GRoup InTERacTIon
(GI) Scoring Guide. Discuss with the
class your expectations for group
work, and review Group Interaction
Student Sheet 1, “Evaluating Group
Interaction.” more information on
the SEpup assessment system is in
Teacher Resources IV: assessment.
If your students worked through the
“Sustainability” unit, they will be
familiar with the use of science
notebooks in this course. If not,
explain that as they conduct activi-
ties, they will record data, observa-
tions, hypotheses, conclusions, and
thoughts in their notebooks.
Keeping a science notebook helps
students track data, note questions as
they arise in investigations and dis-
cussion, and build science-writing
skills. Decide how you would like
students to record their work in each
of the activities in this unit. For
recommendations and more infor-
mation on science notebooks, see
Teacher Resources III: Literacy.
3 use a jigsaw to form groups of
four students. a jigsaw has students
split into groups to learn about a
specific topic, in this instance to read
a case study. Then they return to their regular groups of
four and teach each other what they have just learned.
Explain that there are four case studies in this activity and
that it is important for all students to be familiar with all
four. However, each student in a group will take responsi-
bility for one of the case studies—reading it with a student
from another group, and reporting on the case to his or her
own group members. allow a couple of minutes for groups
to decide (or assign, if necessary) which case study each stu-
dent in a group will read.
4 (LITERacy) all of the readings in this course provide an
opportunity to improve students’ reading ability and com-
prehension through various strategies. model the strategy
“Read, Think, and Take note” for students as you read a
newspaper article. “Read, Think, and Take note” is an oppor-
tunity for students to record thoughts, reactions, or ques-
tions on sticky notes as they read. The notes serve to make
concrete the thoughts arising in their minds and then serve
as prompts to generate conversation or write explanations.
Throughout this unit and the rest of Science and Global Issues
46
SCIENCE & GLOBAL ISSUES/BIOLOGY • ECOLOGY
MATERIALS
FOR EACH STUDENTFOR EACH STUDENT
3 sticky notesy
Student Sheet 1.1, “Case Study Comparison”, y p
Procedure 1. In your group, assign one student to each case study in this activity.
2. Following your teacher’s directions, partner with someone from another
group who is reading the same case study.
3. You and your partner will silently read your assigned case study. As you read,
use the “Read, Think, and Take Note” strategy. To do this:
Stop at least three times during the reading to mark on a sticky note your•
thoughts and questions about the reading. Use the list of guidelines below
to start your thinking.
Read, Think, and Take Note: Guidelines
As you read, from time to time, write one of the following on a sticky note:
Explain a thought or reaction to something you read.•
Note something in the reading that is confusing or unfamiliar.•
List a word that you do not know.•
Describe a connection to something you learned or read previously.•
Make a statement about the reading.•
Pose a question about the reading.•
Draw a diagram or picture of an idea or connection.•
b
aSome examples of the diverse ecosystems found on the earth include islands and atolls (a) and hot springs (b).
2
4
3
ecosysteMs and change • activity 1
75
you will see multiple opportunities for students to employ
and become comfortable with this strategy. Explain to stu-
dents that through these literacy strategies they are learning
the ways in which proficient readers think while reading.
Display the guidelines shown on Literacy Transparency 3,
“Read, Think, and Take note,” in your classroom for students
to refer to. Look for additional occasions for students to
apply this strategy when reading text. For more information
on “Read, Think, and Take note,” see Teacher Resources III:
Literacy.
pair up students from different groups who are reading the
same case study. Give each pair sufficient time to read their
assigned case study, while applying the “Read, Think, and
Take note” literacy strategy. after students have finished
reading, have them compare sticky notes, discuss what they
wrote, and answer each other’s questions if they are able to.
Then, pass out Student Sheet 1.1, “case Study comparison,”
and ask students to complete the appropriate column. ask
each pair of students to make a diagram that shows the
changes and the effects of the changes that were described in
the case study. although there is no right or wrong way to
draw such a diagram, it may help to show one or two exam-
ples of possible diagrams to the class.
Sample cauSe-and-effect diagram for caSe Study 1
76
science and global issues/biology • ecologyscience and global issues/biology • ecology
76
5 Have students return to their
original groups, and allow sufficient
time for them to each briefly sum-
marizetheirassignedcasestudyfor
their other group members. Stu-
dents should refer to their cause-
and-effect diagrams to help with
their summaries. after hearing each
summary, all group members
should have the opportunity to ask
clarifying questions and then com-
plete the column on Student
Sheet 1.1 for that case. a sample of
this sheet appears at the end of this
activity.
follow-uP
6 use the discussions of the case
studies, predictions from procedure
Step 9, and the analysis Questions to
help students understand that change
can affect ecosystems in many dif-
ferent ways. With input from the class,
develop a list of types of changes that
can affect an ecosystem. make sure
that the list includes, or can be
grouped into, sudden or gradual
change, large- or small-scale change,
single- or multi-source causation, and
natural or human causation. Illustrate
each of these changes with examples
from the case studies and other
sources.
7 To help students understand the concepts of com-
bined stresses as part of the answer to analysis Question 3
consider presenting the analogy of an ill person. a par-
ticular disease may be acute or chronic, and both types
can be equally serious but manifest themselves differently.
Sometimes when a person is sick a secondary infection
can have devastating consequences. This is similar to the
effects of the combined stresses that are present in the coral
reef and chesapeake Bay situations.
8 This box lists the key vocabulary developed in this
activity. When words are formally defined in an activity,
they appear in bold type in the list. Encourage students to
include these words when answering the analysis Ques-
tions. also, during informal and formal discussions listen
for these words and see if students are applying them
correctly. Decide how you will support students’ under-
standing of the vocabulary—perhaps with a student glos-
sary, or setting up a class word wall. For more suggestions
on ways to develop students’ understanding of and profi-
ciency with scientific vocabulary, see the Vocabulary section
of Teacher Resource III: Literacy.
ECOSYSTEMS AND CHANGE • ACTIVITY 1
47
After writing a thought or question on a sticky note, place it next to•
the word, phrase, sentence, or paragraph in the reading that prompted
your note.
4. Discuss with your partner the thoughts and questions you had while
reading.
5. Discuss with your partner the causes of ecosystem changes in your study,
and each fi ll in the column on your case study on Student Sheet 1.1, “Case
Study Comparison.”
6. Follow your teacher’s directions to complete a diagram that shows the con-
nections between the events described in the case study you read.
7. Return to your original group and summarize for the other members of
your group what you have learned from the case study. Show the diagram
you drew and Student Sheet 1.1, “Case Study Comparison,” to help you
with your summary.
8. Use the information provided by your group to complete the remaining
columns on Student Sheet 1.1, “Case Study Comparison.”
9. For each of the case studies, develop a prediction of what might happen in
50 years if nothing is done to further infl uence the situation described.
Write your prediction in your science notebook. Include the reasoning
behind your prediction.
10. Follow your teacher’s directions in sharing your prediction with the rest of
the class.
Analysis 1. For each case study, write one to three sentences that summarize the
changes that occurred in each ecosystem.
2. Group the causes of the changes you listed in Question 1 as “naturally
occurring” or “human-caused.”
3. According to the information the case studies provide, what types of
changes seem to make an ecosystem less sustainable? Explain your answer.
4. Use the predictions that were developed in Procedure Step 9 to infer how
the diversity of organisms might change over the next 50 years in the loca-
tions described in each case study. Explain your answer.
KEY VOCABULARY
ecology sustainability
ecosystem sustainable
5
6
7
8
77
ecosysteMs and change • activity 1
77
saMPle ResPonses
1. Case Study 1: The Crab Jubilee
Increased crab harvesting along
with pollution have decreased the
blue crab population in chesa-
peake Bay. This decrease has caused
job losses in traditional industries,
such as crab fishing, and economic
hardship.
SCIENCE & GLOBAL ISSUES/BIOLOGY • ECOLOGY
48
IMAGINE WALKING ALONG the Chesa-
peake Bay shoreline in Maryland or
Virginia and looking for crabs to
catch. To your surprise you come
across hundreds, maybe thousands,
of crabs crowded together in
shallow water and on the shore.
You will eat well tonight! Locals
call this a “crab jubilee,” and it is an
event that people have witnessed
many times in the past. Probably
Native Americans saw this phe-
nomenon thousands of years ago.
As the human population of the
region has increased, so has the
frequency of the “crab jubilees.”
This may sound good if you like to
eat crab, but in fact, it is a sign of
problems in Chesapeake Bay.
The name Chesapeake is derived
from a Native American word
meaning “great shellfi sh bay,” and
shellfi sh have always been an
important food source for the
people in the area. The blue crab
(Callinectes sapidus) has been har-
vested commercially in the bay
CASE STUDY 1
The Crab Jubilee
A “crab jubilee” on the shore of
Chesapeake Bay
science and global issues/biology • ecology
78
ECOSYSTEMS AND CHANGE • ACTIVITY 1
49
since the mid-1800s. Over the years
more and more crabs have been
harvested, with 1993 having a
record catch—347 million crabs
worth $107 million. Since that
time, however, the number of crabs
harvested has declined. In 2007 the
number had dropped to 132 million,
with a value of $52 million. In 1999,
more than 11,000 people in the area
had crab-related jobs, but in 2006,
fewer than 7,000 were involved in
the crab industry. The effect on the
regional economy was so severe that
in 2008 the U.S. Department of
Commerce declared a commercial
fi shery failure.
One of the factors thought to have
contributed to the failure of the
blue crab fi sheries is overfi shing.
To keep the crab populations stable
a certain minimum num ber of
egg-producing crabs must survive
each year. Scientists have estimated
that the crab population would
not decline as long as the number
of crabs har vested each year did
not exceed 46% of the total crab
pop ulation. However, over the
past decade it is estimated that an
average of 62% of all of the blue
crabs in the bay were caught
each year.
The other problem is pollution of
the bay’s waters from chemicals
and sediment that have washed
into the bay from such sources as
farms, sewage treatment plants,
suburban lawns, and golf courses.
Nitrogen- and phosphorus-
containing chemicals from these
sources have increased the growth
of algae in the bay. The algae and
the sediment make the waters
cloudy enough to limit the amount
of sunlight that reaches the bottom
and to impede the growth of
underwater plants. Eelgrass, in par-
ticular, is crucial to crab popula-
tions because tiny crab larvae
blend in with the grass and are less
visible to predators. Without the
grass fewer of the young crabs
reach maturity.
When the algae die they fall to the
bottom of the bay. As bacteria
decompose the dead algae, they
remove much of the oxygen from
the water. These oxygen-deprived
areas cannot support life, and
organisms that cannot move else-
where die, creating dead zones.
Crabs moving out of the dead
zones may end up in great num-
bers on land where the oxygen
levels are higher. This is the reason
for the “crab jubilees.” Although
dead zones can develop as the
result of natural phenomena, such
as changes in ocean current pat-
terns, scientists believe that dead
zones indicate that human activi-
ties are increasing the frequency of
“crab jubilees,” and are ultimately
affecting the sustainability of the
crab population. �
Blue crab (Callinectes sapidus)
ecosysteMs and change • activity 1
79
Case Study 2:
The March of the Toads
once introduced into australia,
cane toads quickly acclimated to
various environments and spread
rapidly. In some cases the increase
in cane toad populations has
decreased the populations of native
animals significantly.
SCIENCE & GLOBAL ISSUES/BIOLOGY • ECOLOGY
50
Dozens of cane toads(Bufo marinus)pile on top of one another.
Cane toad distribution 1935–2008
THEY DON’T BELONG in Australia,
but there are already 200 million
of them there. They can travel as
far as 50 km (31 miles) a day and
continue to spread across large
areas of the country. They may
feed as often as 200 times in a
night, but almost everything that
tries to eat them dies of heart
failure. Who are these invaders?
These are cane toads.
The cane toad (Bufo marinus)
is a large and poisonous animal
that is native to Central and
South America. Because the toad
had been introduced to various
regions in the world in an attempt
to control pests in cane fi elds,
Australian authorities in 1935
approved the importation of cane
toads to the Australian province
of Queensland. About 100 were
shipped in, allowed to breed in
captivity, and were released into
several sugar cane
plantations where two
types of beetles were
ruining the crop.
Although the cane
toads would certainly
eat the beetles, it turned
out that they didn’t
encounter the beetles
frequently enough
to eat many of them.
One reason is that the
beetles lived mainly in
the higher parts of the
sugar cane plants out
of the toads’ jumping
range. Another reason
is that the beetle only
CASE STUDY 2
The March of the Toads
science and global issues/biology • ecology
80
ECOSYSTEMS AND CHANGE • ACTIVITY 1
51
invaded the sugar cane fi elds at the
time of year when the cane toads
didn’t go there because of the lack
of protective plant cover. In addi-
tion, the beetles were most active
during the day, but the cane toads
fed mainly at night. The toads
didn’t go hungry though, as they ate
pretty much anything that would
fi t into their mouths—including
insects, frogs, small reptiles, mam-
mals, and birds—eventually dimin-
ishing the biodiversity of the areas
they were invading.
A female cane toad can produce
around 35,000 eggs every time she
mates, which can happen several
times a year. They lay their eggs in
almost any body of water, large or
small, fresh or salt. Because cane
toads can survive in a wide range of
conditions, they adjusted well to
the environment in Queens land
and began to spread to other parts
of Australia. Australia has no
natural predator that can control
the cane toad populations, but the
cane toad has made its mark on
populations of many other ani-
mals. The cane toad adult has
poison glands in its skin, and the
tadpoles are highly toxic to most
animals. Most of the Australian
predators that eat them die of heart
failure. Even crocodiles are not
immune, and since 2005, after cane
toads invaded the Victoria River
district of Australia’s Northern
Territory, there has been a 77%
decline in the freshwater crocodile
population.
Also, where cane toads are present,
local populations of northern
quoll have disappeared. Rabbit-
sized marsupials that eat a wide
variety of prey, quoll often die from
eating cane toads. The popula-
tion of northern
quoll is parti cularly
vulnerable to extinc-
tion because the males
die after mating when
they are one year old.
When this natural loss
is accelerated by
the losses caused
by the cane toads,
quoll populations
quickly become
unsustainable.
Cane toads are
causing yet other
problems. They
are suspected in
reducing the numbers of
animals that abori ginal
bushmen traditionally rely
on as food sources. The
toads are known to eat pet
food and feces, the latter
leading them to carry dis-
eases, such as salmonella. In
2001 the cane toads reached
the carefully conserved
Kakadu National Park,
raising fears that the toads
will disturb the delicate bal-
ance of species in the park
and reduce its biodiversity. Local
economies may be affected
if tourism suffers as a result of
changes to the park. �
Northern quoll(Dasyurus hallucatus) (left) often die from eating poisonous cane toads. Thiscrocodile (below) willlikely die from the poison in the cane toad it is eating.
81
ecosysteMs and change • activity 1
Case Study 3:
The Bleaching of the Reefs
coral reefs, which are home to mil-
lions of organisms, have been dam-
aged by unsustainable fishing
practices and by changes in the
oceans. Higher water temperatures
in particular have caused bleaching
of large areas of coral reefs.
SCIENCE & GLOBAL ISSUES/BIOLOGY • ECOLOGY
52
CORAL REEFS OCCUPY a small frac-
tion, about 0.2%, of the earth’s
ocean fl oor. Yet it is estimated that
25% of all marine organisms live
in or around coral reefs and that
nearly one million different spe-
cies can be found there. Coral
reefs support fi shing and provide
building materials for local com-
munities. They also act as natural
breakwaters, protecting coastal
areas. They have great potential
in providing ingredients for new
medicines and are a major attrac-
tion for tourists. These benefi ts,
however, also mean that coral reefs
around the world are under threat.
Coral reefs are made up of millions
of small animals called polyps.
Polyps are invertebrates that fl ourish
in warm and shallow parts of
oceans. These tiny animals rely on
even smaller organisms— algae—
for their survival. These algae are
single-celled, photosynthesize in
the presence of sunlight, and live
in the tissues of the polyps. Most
polyps themselves live inside a hard
external framework that they have
made from minerals in the sea-
water. Large colonies of polyps and
their limestone skeletons form the
coral reefs, some of which are so
large that they can be seen from
space.
Scientists estimate that in the past
50 years more than a quarter of the
world’s reefs have been destroyed.
Today there are no signs that this
CASE STUDY 3
The Bleaching of the Reefs
Coral reef with a diversity of fish
Coral reef distribution
82
science and global issues/biology • ecology
ECOSYSTEMS AND CHANGE • ACTIVITY 1
53
Crown of thorns(Acanthaster planci) seastars (top) can severely damage coral reefs.
This coral (above) has “bleached,” likely due to fluc tu ation in water temperature.
destruction is slowing down. One
source of coral reef damage is
human-generated—in the form of
unsustainable and illegal fi shing
practices, such as when fi shermen
drop dynamite onto the reefs to
help them kill and catch fi sh.
Fishing can also harm coral indi-
rectly. For example, it plays a role
in increasing populations of the
coral- eating sea star called the
crown of thorns. Normally the
number of sea stars living in a reef
is low, as several species of reef
organisms prey on the young sea
stars. However, when too many of
these predators are caught by fi sh-
ermen, many more sea stars sur-
vive to become adults and eat up
much more of the reef—up to 90%
in some cases.
Another major threat to coral reefs
is climate change, which is a global
problem. Coral reefs are sensitive to
changes in ocean temperatures, and
many are in areas where the tem-
perature is already close to the
upper limit in which a reef can sur-
vive. A water temperature increase
of as little as 1°C can decrease the
ability of the coral algae to photo-
synthesize. It can sometimes cause
the polyps to expel the algae. In
both situations the coral loses its
color and looks “bleached” or white,
indicating that it is under stress.
Warmer ocean temperatures also
favor the growth of bacteria that
cause diseases in the coral reefs.
Compounding those problems, the
increase of carbon dioxide gas in the
atmosphere is making the world’s
oceans more acidic. This reduces
the concentration of some of the
chemicals that the polyps use to
build the limestone skeletons and
further weakens the coral reefs.
In 1997 and 1998, coral reefs all
over the world suffered extensive
bleaching. More than 50% of the
Great Barrier Reef in
Australia was
affected and at least
50% of the reefs in
Palau in the South
Pacifi c were killed.
The following year
tourism in Palau was
down 10%. Coral
reefs hold the largest
biodiversity in the
oceans and are esti-
mated to contribute
more than $20 bil-
lion to local econo-
mies around the
world. All ecosys-
tems, fortunately,
have a certain level
of resiliency, and,
provided the tipping
point isn’t reached,
change does not
always have to have
permanent negative
effects. Should the
ocean temperature go back down,
some of the coral might recover.
However, to reverse the ocean
warming will require tremendous
human effort, and it will be
expensive. Can the world, how-
ever, afford to continue losing its
coral reefs and the biodiversity
within them? �
83
ecosysteMs and change • activity 1
Case Study 4:
The Yellowstone Fires of 1988
The 1988 fires, natural and human-
caused, affected large areas of yellow-
stone national park. although many
plants were burned and a number of
animals were killed, the area has
recovered. Beneficial effects of the fire
included allowing certain seeds to
germinate, enriching the soil, and
creating space for new plants to grow.
2. See the sample chart below. Students
may list other changes, some of
which they might consider natural.
For example, they may suggest that
the impact of the crown of thorns sea
star on coral reefs is natural since the
reef is a natural food source for the
crown of thorns. acknowledge that
this, and other changes they suggest,
might be natural but that the prob-
lems described in the case study occur
when humans disrupt the balance of
these natural relationships. For exam-
ple, humans are the cause of the over-
fishing of sea star predators, which
leads to an overabundance in the
number of sea stars. The presence of
more sea stars results in larger areas
of a reef being consumed.
3. The changes that were caused by humans seem to have had
the most severe negative effects and would therefore make
an eco system less sustainable. Sometimes the change was
rapid, such as the introduction of cane toads. other times
the change was more gradual but the negative effects were
greater. In two of the four case studies, the sustainability of
the eco systems was lowered due to a combination of
changes (fishing practices and changes in the oceans for
coral reefs, pollution and overfishing in chesa peake Bay).
4. Exact answers will vary, depending on students’ predic-
tions. The biodiversity, however, will likely decrease in all
of the situations except yellowstone. In case studies 1, 2,
and 3 both the number and types of organisms are
decreasing. Specifically, the cane toad study mentions local
extinctions of the northern quoll and large reductions in
the number of freshwater crocodiles. The reef article
describeslargereductionsinthesizesofcoralreefsand
mentions the vast number of species that are typically
found near and in reefs. Some, perhaps many, of these
species would decline as the reefs decline. The crab article
notes the decrease in eelgrass as well as the blue crabs,
anditreferstodeadzoneswherenothinglives.
SCIENCE & GLOBAL ISSUES/BIOLOGY • ECOLOGY
54
OVER SEVERAL DAYS in
August 1988, many towns
close to Yellowstone
National Park experienced
smoke so thick that drivers
had to turn on their head-
lights in the middle of the
day. People were advised to
stay indoors to avoid
breathing the smoke-fi lled
air. Some communities in
and around the park were
temporarily evacuated as
the worst fi res ever
recorded in Yellowstone
burned out of control. By
the fall of 1988, more than
CASE STUDY 4
The Yellowstone Fires of 1988
Fires sweep through Yellowstone in 1988.
Areas burned by the 1988 fires in Yellowstone
Sample Student Response to Analysis Question 2
Natural Human-caused
• lightening-causedfires
• fires
• introductionofcanetoads
• coralreefdamagecausedbycertainfishingpracticesandchangestotheoceans
• pollutioninChesapeakeBay
• overfishingofbluecrabs
84
science and global issues/biology • ecology
Revisit the challenge
The sustainability of an ecosystem is
influenced by humans’ environmental,
economic, and social considerations.
Ecosystems may gradually or suddenly
undergo permanent change, or they
may exhibit resiliency by responding in
awaythatminimizesthechange.Sus-
tainability is threatened when the
damage is greater than the resiliency of
the ecosystem. There seems to be a bio-
diversity threshold in an ecosystem
below which the likelihood of recovery
from adverse change is highly
diminished.
ask students to describe changes they
may have seen or heard about in an eco-
system. To help prompt a class discus-
sion consider having several resources
available, such as relevant newspaper,
magazine,andonlinearticles.(National
Geographic is a good place to start.)
alternatively, you might ask students to
find and present relevant articles.
Finally, remind students that this is an
introductory activity and that they will
explore each concept further as they
progress through the unit.
ECOSYSTEMS AND CHANGE • ACTIVITY 1
55
25,000 fi refi ghters had worked on
controlling the fi res and over one
third of Yellowstone National Park
had burned.
Yet at the start of the summer of
that year there were few indications
of the scale of what was to come.
The previous six summers and the
spring of 1988 had all been wetter
than normal, and fi re activity had
been low. The lack of fi re had led to
a buildup of old trees and under-
brush in the forests of Yellowstone.
This was fuel that was ready to
burn if the conditions were right.
The summer of 1988 turned out to
be the driest in the park’s history.
By the middle of July, 8,500 acres of
the area had burned.
Within two weeks the area af fected
by fi re had increased by a factor of
10 and on August 20 winds of about
130 km/h (80 mph) helped to
double the size of the fi res in a single
day. Lightning caused most of the
fi res, but humans caused three of
the largest. The fi rst snows in
September signifi cantly
dampened the fi res, and
they were all extin-
guished before winter
arrived. Concern was
expressed across the
country about the
impacts of the fi res on
wildlife, vegetation,
tourism, and local econo-
mies. There was much
discussion about whether
the fi res should have
been put out earlier when
they were still small.
Nearly all of Yellowstone’s plant
communities have burned at some
time in the past. Scientists think
that fi res in Yellowstone naturally
burn at intervals varying from
20 to 300 years, depending on the
location and type of vegetation.
While fi re can be a destructive
force, it also stimulates growth in
the park. Soil receives nutrients
from burned plant materials, and
when forests burn, more sunlight
reaches the ground. Both of these
processes help plants to grow.
Studying the Yellowstone fi res
and other fi res has provided scien-
tists with evidence that allowing
periodic fi res, instead of always
preventing them, can benefi t eco-
systems. Periodic fi res both prevent
the build up of woody debris that
can make fi res much larger and
stimulates growth in the forest.
Over hundreds of years the burned
areas will progress through a
variety of stages as they recover.
(Continued on next page)This area is beginning to recover after the Yellowstone fires.
85
ecosysteMs and change • activity 1
SCIENCE & GLOBAL ISSUES/BIOLOGY • ECOLOGY
56
(Continued from previous page)
This process is called succession.
Wildfl owers, grasses, and sagebrush
may be the fi rst to grow, but soon
aspen trees will begin to sprout.
Aspen has a thin bark and burns
readily in a fi re. But while the part
of the tree aboveground is damaged
or destroyed, the extensive under-
ground network of roots is pro-
tected from the heat of the fl ames
by the soil, so it isn’t long after the
fi re is out before shoots begin to
grow. Unlike the aspen, Douglas fi r
trees have very thick bark that insu-
lates most of the tree from the heat.
Such trees are very resilient and can
often survive fi res. Lodgepole pine,
which makes up 80% of the forests
of Yellowstone, has thin bark and
the trees burn readily in fi res, but it
also benefi ts from fi re. This tree
produces cones that are glued shut
by resin. Only the heat of a fi re is
enough to melt the resin and allow
the cone to open for the seeds inside
to disperse. Since the seeds will be
produced after the ground has been
cleared and enriched by fi re, they
are more likely to grow.
Scientists found that 345 elk died
as a direct result of the fi res, which
is less than 1% of the elk popula-
tion. During the winter following
the fi re, thousands of elk died
from lack of food, but the num-
bers of elk had recovered com-
pletely within fi ve years. The fi res
also killed some fi sh, 36 deer, 12
moose, 6 black bears, 9 bison, and
possibly 1 grizzly bear. The car-
casses of these animals provided
food for other animals, such as
coyotes, bears, and some birds.
Dead trees provided more places
for birds like woodpeckers and
bluebirds to fi nd holes in which to
build their nests. Overall there
does not seem to have been a sig-
nifi cant long-term negative effect
on animal populations. The fi res
did have an effect on tourism
while they were occurring, but the
infl ux of fi refi ghters and the
media made up for this to some
degree. There was no decrease in
the number of tourists who visited
the region the following year. �
—Adapted from National Park Service,
“Wildland Fire in Yellowstone.”
©20
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science & global issues/ecology student sheet 1.1
The Crab JubileeThe March of the Toads
The Bleaching of the Reefs
The Yellowstone Fires of 1988
Localcausesofchanges
overfishing
increaseinhumanpopulation
introductionofcanetoadstosugarcanefields
fishingpractices,suchasoverfishinganduseofdynamite
humanactivity
buildupofoldtreesandunderbrush
lightning
Globalcausesofchanges
increaseinhumanpopulation
pollution
none globalclimatechangecausingwarmeroceantemperaturesandincreasedoceanacidity
changingweatherpatternsthatledtoverydryconditions
Environmentaleffects
cloudierwater
lesseelgrass
lessprotectionforyoungcrabs
lowoxygenlevels
deadzones
lossofbiodiversity
manyorganismseatenbycanetoads
somelocalpopula-tionsbecameextinct
lossofbiodiversity
fewerreefs
weakerreefs
bleachingofcoral
increasedbacterialgrowth/disease
lossofbiodiversity
fire,smoke,lackoffoodlethal/harmfulforsomeanimals
enrichedsoilandmoresunlightonsoil—moreplantgrowth
someincreasedgermination
Economiceffects fewercrabstocatch
fewerjobsrelatedtocrabs—fishing,tour-ism,restaurants,etc.
possiblelossofmoneyfromreducedtourism
moneyspenttryingtocontrolthecanetoadpopulationsandontreatingaffectedorganisms
lessprotectionforcoastalcommunities
lessmoneyfromtourism
reducedfishingbothlocallyandfartheraway
short-termlossofjobsandmoneyfromtourism
increasedbusinessfromfirefighters
Socialeffects somefamiliesthathavereliedoncrab-relatedjobsmustfinddifferentwork
familiesmovefromtheregion
lossoftraditionalfoodsourcesforaboriginalbushmen
somefamiliesthathavetraditionallyreliedonthereefshavetofindnewjobsormovetodifferentplaces
lossofbeautyofreefs
short-termchangeinnumbersofjobs(e.g.,fewertourguides,etc.)
concernsaboutlivingwheretheremightbeanotherlargefire
humanhealthimpact(makesasthmaworse)
lossofbeautyoflandscape
Case Study Comparison
name ___________________________________________________________________________________ date __________________________SampleStudentResponse