Ecosystems and Change - Polytech High School · 2014-11-21 · Ecosystems are constantly c han gin —sometimes in ra dual an ardly noticeable ways an sometimes rap-idly and dramatically

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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


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

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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

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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.


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


78


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)


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.


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


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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


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.


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


Coral reef with a diversity of fish

Coral reef distribution

82



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


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.


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


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


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.


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



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.”

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science & global issues/ecology student sheet 1.1

The Crab JubileeThe March of the Toads



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

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Ecosystems and Change - Polytech High School · 2014-11-21 · Ecosystems are constantly c han gin —sometimes in ra dual an ardly noticeable ways an sometimes rap-idly and dramatically